Proform 750 CFM DP carburetor tuning?

[Nickrc3]

I recently installed a Proform #67213-750 DP carburetor (see related thread within Performance forum) on my 440 Charger and appear to have some issues with tuneability and an excessive 'rich' condition at idle. The 'gassy' exhaust scent is quite evident, though no visual black smoke exits the tailpipes. I pulled the new NGK sparkplugs and observed they were loaded with black carbon - not wet, just carbonized.
Acceleration and high speed does not appear affected; the car moves like a raped ape, however, once the engine is shut down, it become difficult to restart. It cranks over fine and gas is present in carb, but won't actually fire. After she sits (say five minutes), she'll restart. Loaded-up?

No float level adjustments were made, as the fuel level is clearly centered within the sight glass. Air/Fuel mixture screws (4) were adjusted, however, there's a limited range of this adjustment. Currently, I have them set at 3/4 turns out from seated position. This provides the highest vacuum rating (15") w/ RPM. Any adjustment outside of one full turn does result in a rougher idle and lower vacuum levels. I have pinpointed carb cleaner spray around the intake/head areas, carb flange, and all vacuum fittings - no change in RPM's

My questions surround the tuning of this carb. Should I focus on the visual air bleed jets (8 total) located above venturi's? Primary side only?
. High speed's are #31's and idle's are #70. Would replacing the idle air bleed jets (primary side only) from the #70 to a larger number increase air quantity, thus leaning the idle mixture?
Would I need to consider changing the internal primary main jet size, which are now #74's?

Lastly, I couldn't locate a source for tuning these 4-corner carburetors. I realize they're Holley clones, but are there any useful links or publications that specifically address these carburetors?

Thanks Guys!

[BSB67]

You can first try increasing the size of all of the IAB to see if that helps.  No, you do not need to change the main jets.

I have had similar condition, but on a Holley.  Reducing the IFR fixed it.

[firefighter3931]

You can first try increasing the size of all of the IAB to see if that helps.  No, you do not need to change the main jets.

I have had similar condition, but on a Holley.  Reducing the IFR fixed it.

Hi Nick,

I would make sure the choke is functioning properly and not staying closed too long. Spray some carb cleaner down the idle bleeds to clear them out in case there is some debris in there.

As Russ indicated above....an idle bleed swap on all 4 corners will help. 



Ron

[Nickrc3]

I would make sure the choke is functioning properly and not staying closed too long.

The choke does fully open at warm-up and remains open throughout running.
I did locate an interesting article from Holley's technical bulletin regarding the electric choke installation, which contradicts my method:
NOTE: Holley does not recommend using the 12V side of the coil for your power source.
WARNING: Connecting the choke cap to the ignition coil will result in unacceptable choke operation, and could cause
engine misfiring, resulting in possible engine damage. Do not connect the choke wire to the coil!
The article mentioned the improper installation will place an increased load (or draw) away from the coil and may affect the voltage/energy directed to the spark plug. 

Regarding the idle air bleed jets - only increase both pairs (four total) of the #70's? Increase how large -say 74?

Thanks again.

[firefighter3931]

Nick,

I agree with the holley website regarding powering any accessory off of the ignition circuit. At lower engine speeds the alternator output is low and overloading any one circuit is not good. I would try disconnecting the choke and wiring the flap open and see if that helps....or wire it to some other 12v switched source. 

As for the idle bleeds I would go up a max of 2 sizes at a time. 


Ron

[69wannabe]

Just wondering if you have a heat insulator spacer under your carb and if i'm not mistaken the float level is supposed to be at the bottom of the sight glass on a proform carb. These will cause it to be hard to start when the engine is warm. Also where is your initial timing set on the engine? Low base timing will cause a rich fuel smell at the tailpipes. It will smell alot more when its cold since the engine is'nt warmed up and its is'nt burning all the fuel as good as it will when it is at operating temperature. I had the same issues and bought a holley carb which ran a lil better but until I got my timing and heat insulator on there I was having the same issues you are having.

[NHCharger]

Nick,

I just installed the same carb. I emailed Proform to ask for any type of manual. They have nothing. As mentioned it's based on a Holley. I've checked out some online vids about tuning a Holley. All the videos say the float level should be at the bottom of the viewing port/sight glass.

[Nickrc3]

I just installed the same carb. I emailed Proform to ask for any type of manual. They have nothing. As mentioned it's based on a Holley. I've checked out some online vids about tuning a Holley. All the videos say the float level should be at the bottom of the viewing port/sight glass.

I also, repeatedly, tried to obtain some technical support (written or verbal) from the ProForm folks; get the same ding-a-ling that transfers me around until I end up with a voice message. So much for customer support...

My research into different automotive forums has revealed a few identical conditions which steer into the direction of increasing the idle air bleed (IAB) jets and/or readjusting the idle speed screw. This adjustment will either expose or cover the rectangular transfer slot under the baseplate. Depending on its position, will greatly affect the range of tunability with the four idle-mixture screws. That is exactly what I'm experiencing; fouled plugs, difficult start after running, and an exhaust smell that will make you puke.
I will order larger IAB jets, as this may certainly resolve matters too.

All the videos say the float level should be at the bottom of the viewing port/sight glass.

NH Charger - I also have read that and may adjust, though cannot understand why a level fuel condition would throw off the idle-mixture screws so much.

Thanks Guys- really appreciate all your input. Keep it coming...

[firefighter3931]

Hey Guys,

The Proform carbs are basicly the same as what QuickFuel offers. Proform uses Quickfuel baseplates/metering blocks/bowls on their carburators.....Quickfuel uses ProForm main bodies on theirs. 

The correct fuel level float adjustment is midway up the site glass. Different from Holley which has it at the bottom of the site hole. 

Nick ; if you have too much of the transfer slot exposed it will richen up the idle circuit. There should be a secondary throttle adjustment screw that will allow more air into secondary venturi at idle. You will probably have to crack those secondary blades open a bit. Sometimes you will have to drill small holes in the throttle blades to allow more air in at idle but this is a last resort.

I would check to see if you can open the secondary blades a bit and see if that helps. Doing this should allow you to reduce the idle speed adjustment and reduce the transfer slot exposure. Too much exposure means it's running on the main circuit....and that will make it very rich @ idle.


Ron

[Nickrc3]

if you have too much of the transfer slot exposed it will richen up the idle circuit

Ron, I believe you nailed it  , however, I cannot confirm until this weekend as the car sleeps during the work week (stored in a warehouse).

My research revealed this outstanding article which I encourage all novice Holley tuners to print and save:
http://members.tccoa.com/392bird/tuning.htm.
It accurately describes my conditions and its remedy (as Ron mentioned).

I took the time to compose a rather lengthy E-mail to the ProForm (Parts Specialty) folks last night on my dilemma. This morning, I received a phone call from ProForm. Their Technician, 'Rick', took the time to provide a simple flowchart of diagnosis procedures. He immediately focused on the fact that the transfer slot is likely 'over exposed' disturbing the idle circuit and reducing tuneability with the idle-mixtures screws. He also mentioned the Allen adjustment screw which control the secondary throttle plates is accessible from the top of the base plate? Not sure on that, as I read you make the adjustment from the bottom of the baseplate.
Rick also confirm the float levels should be centered within the sight glass.

So, Saturday morning I'll dig back into it and post results.

Question: once spark plugs are fouled, can they be effectively be cleaned and reused? I was thinking on letting them soak in Acetone overnight and attempt to clean. Just replaced them two weeks back...

Thanks Guys!

[BSB67]

if you have too much of the transfer slot exposed it will richen up the idle circuit

Ron, I believe you nailed it  , however, I cannot confirm until this weekend as the car sleeps during the work week (stored in a warehouse).

My research revealed this outstanding article which I encourage all novice Holley tuners to print and save:
http://members.tccoa.com/392bird/tuning.htm.
It accurately describes my conditions and its remedy (as Ron mentioned).

I took the time to compose a rather lengthy E-mail to the ProForm (Parts Specialty) folks last night on my dilemma. This morning, I received a phone call from ProForm. Their Technician, 'Rick', took the time to provide a simple flowchart of diagnosis procedures. He immediately focused on the fact that the transfer slot is likely 'over exposed' disturbing the idle circuit and reducing tuneability with the idle-mixtures screws. He also mentioned the Allen adjustment screw which control the secondary throttle plates is accessible from the top of the base plate? Not sure on that, as I read you make the adjustment from the bottom of the baseplate.
Rick also confirm the float levels should be centered within the sight glass.

So, Saturday morning I'll dig back into it and post results.

Question: once spark plugs are fouled, can they be effectively be cleaned and reused? I was thinking on letting them soak in Acetone overnight and attempt to clean. Just replaced them two weeks back...

Thanks Guys!

Do you have a very large cam?  You might be jumping to conclusions prematurely.

[NHCharger]

Good info Ron. I need to adjust one float, can't even see the fuel level because it's so high.
Ran the car last night to check a few issues, with the garage door open and a large fan blowing my wife could smell the fumes while walking the dog 100 yards down the road. She said this will be great for pest control when black fly season starts in a few weeks Hoping it won't take that long to dial in.

Nick-Nice link. Carb function and tuning is the one area I need to work on.

[Nickrc3]

Do you have a very large cam?  You might be jumping to conclusions prematurely.

I've got the old Mopar 'purpleshaft' 284/484 camshaft which, from my recent knowledge, does have it's tuning issues.
The article listed in my past reply describes a remedy for aggressive cams, again as Ron stated, to drill the throttle plates. I mentioned this to the ProForm rep in my telephone conversation (who is a Mopar guy and was familiar with this specific grind). He claims the drilling would likely Not be necessary.
Fingers crossed...

[Nickrc3]

Tonight, I was able to remove the carburetor and observed this:

Note the overly exposed transfer slot within the primary venturi. I've read the slot should appear as long as wide or .020" in size.
Here's the secondary adjustment Allen screw, tweaked after the primary T-slot is set. The secondary adjustment can only be made from under the baseplate, however, I believe the Allen screw can be removed, then reinstalled from the top to aid in future adjustments.


All spark plugs fouled:


Purchased one of those Harbor Freight spark plug cleaners - $11.99. Review forthcoming.

Mosquito's coming out now. Tomorrow morning (Saturday) I'll complete the adjustments and redo the positive lead to the coil.
Results to follow...

[tracpack440]

 

[firefighter3931]

Yep....looks like to much transfer slot exposed. 

Keep at it Nick....you're on the right path. 



Ron

[NHCharger]

Keep us updated on this. I'll probably need to do the same thing. Right now fixing the rich idle problem is #12 on my Charger punch list.

[Nickrc3]

UPDATE: Firsthand, this Harbor Freight spark plug cleaner is quite a purchase for $11.99.

Before:

...and after a 15-second cleaning:


O.K. - With both Primary & Secondary throttle blades now adjusted to expose that 'square' or .020" fuel transfer slot, I reinstalled the carburetor, along with a vacuum gauge and tachometer.
The electric choke wiring was also revised. Since the washer pump wire is a 12 volt switched source, I carefully spliced the brown conductor within the harness and fed the choke housing.

Upon initial start-up, the engine ran terribly, shaking violently. Since I had inverted that Allen screw for the secondary idle, adjustments were quickly made from the top, however, the pump actuator arm blocks the screw head, requiring engine shutdown to adjust. Holley sells a cool linkage piece that allows such adjustments without engine shutdown. Probably worth the small investment.

After a series of secondary idle tweaks (not touching the curb idle speed adjustment which affects the primary slot exposure), I got the engine to settle down and sustain running, however, the four idle-mixture screws remained ineffective (at 1/2 turn from base) and I still received that 'gassy' exhaust scent. Once engine cooled, the spark plugs were removed. They were all fouled!
Back to the spark plug cleaner for round #2.
More tweaking of the secondary idle screw increased engine RPM's . To reduce to an acceptable level (900 RPM's), I slowly adjusted the curb idle speed screw, closing that primary transfer slot more.  RPM's dropped - good, however,  upon instant acceleration with the carb linkage,  received a slight backfire through the carburetor. I took this as a good sign, indicating I've entered a lean range of tuning with a closed primary throttle blade position.
So, with this lean condition, I focused back to the secondary idle adjustment, reducing the secondary throttle blade opening, then readjusting the curb idle to now slightly open the primary blades.
The entire time monitoring the vacuum gauge:

16.6hg @ 925 RPM idle in Park,  - 15hg in Drive.

I then road-tested the car for approximately 15 miles, which (of course) included two huge burn-out's  I swear, at my age, that 1-2 shift is just orgasmic -  my Space Mountain ride! 
Pleased to say the nasty exhaust smell is gone and the engine never performed better. Outstanding throttle response, very clean transition from idle to 5500 RPM's, and recovery. She's running like a beast, yet tame for urban driving.

Upon return and cool down, I pulled four plugs:
[imghttp://i1002.photobucket.com/albums/af150/Nickrc3/DSC02142.jpg][/img]
Notice the one fouled plug - things are improving. Almost there!

This morning I called 'Rick' from ProForm on results. His diagnosis, as suspected, is to increase the air feeding the idle circuits. This can be accomplished by drilling a 1/16" hole into each primary throttle blade, however, I'm not too keen on this method. I much prefer to swap out the Idle Air Bleeds from a #70 to a #73. JEGS sells all four for $11.00 delivered. This hopefully, will restore the tuneability to the four idle-mixture screws and provide a cleaner burn.

Till next weekend...

[firefighter3931]

Nice work Nick and an excellent writeup ! 

It's surprising how much little changes can make such a huge difference. Just balancing the primary and secondary idle circuits yields huge dividends in idle quality and performance. 

That HF plug cleaner does a fantastic job 



Ron

[GPULLER]

Good to see your making head way on the tuning.  Yes the old MP 484 cam can make it a little difficult to tune.  Your vac looks great, haven't had a gauge on mine since I installed the new dist.  Just played it by ear.
I have an old 750 DP Holley and the secondary adjustment screw is frozen in the base plate.  Have tried heat with no luck to break it loose.  Ended up drilling the primaries too.
Someday a new Quick Fuel carb will come my way.

[NHCharger]

Wow, great follow up. I'm going to try and tackle my carb issues this weekend. And also order one of those spark plug cleaning kits. Pulled one of my plugs, looks almost bad as yours.

[NHCharger]

Pulled my carb tonight, same issue. Way too much transfer slot showing in the primary, nothing showing on the secondary. I used your trick and flipped the allen screw so I can adjust the secondary circuit from the top. Have both adjusted so the slots now look square. After work tomorrow I'll finish installing the carb and try to adjust using the info you provided.
Also ordered one of those spark plug cleaners 

[Nickrc3]

Well, started off this Saturday morning all excited, as I received the #73 idle air bleeds Thursday from JEGS (great prices and quick shipping):


Figured I'd leave the carb bolted down to the manifold and started with replacing the pair of secondary idle air bleeds:


Easy-peasy, then to the primaries. Oh boy, big difference in effort. Removal of the original #70's went fine with my custom jet installation tool, 

I carefully fed it through between the choke plate and onto the vacant opening, attempting to start that first thread, while ever-so-cautious not to strip the aluminum female thread within the carb body. After an hour of struggling to install the remaining two air bleeds, laying over the radiator support and changing multiple eye glasses just to see the damn thing, I pull the tool out and the jet pulls free from the tape!      No, this brass booger can't simply fall into the venturi or the front of the valley pan (both stuffed with rags). Where does it fall? Right straight down inside the cylinder head heat riser! 


I actually heard it rattle down the riser. Oh well, it's gone. I'll have to reinstall the old #70.
Just for the hell-of-it, I rigged this wire with some of that 'Gorilla' duct tape looped over, since a magnetic pickup won't work. Unbelievably first time in the well, I snagged it.         


So, with bruised sides, eyes strained and a sudden headache, I decide to remove the carb. Ten minutes later, the engine is running with the new idle air bleeds installed. Boy, did I feel ridiculous not doing this initially!
Word of advise: take the carb off the engine to perform these changes, and buy the tool:


O.K. - engine running similar with the #70's installed, however, I actually did have more range of adjustment with the four idle-mixture screws. Now, I can observe the vacuum and RPM's deteriorating as the idle-mixture screws are adjusted closer to their seat. This is a good sign! Before (with the #70's) the engine actually ran pretty well with all screws lightly seated. I'm finally increasing air quantity!
With all four idle-mixture screws set 3/4 out from base, vacuum levels peaked at 17"Hg - RPM's-850 in Park. Didn't check plugs, as I didn't need to strip any spark plug threads or burn my hands! Probably still need to continue moving up the idle air bleed jets, maybe to #78's. Comments?

So after my usual test runs and ingesting my weekend dose of that lovely aroma 'Scent of Dayton GT's'   , I left well-enough alone. Too beat up at this point...

One interesting note, I stopped to top off the gas tank (BJ's Wholesale - 93 octane -$4.02 gal) and she would not restart; cranking over quickly, but no spark.
Popped the hood and check the carb squirters; plenty of gas. Likely, I flooded it.
After allowing her to rest maybe sixty seconds, engine restarted and ran fine.
I'm now thinking the plugs are continuing to foul    Comments?

Thanks Guys.

[justcruisin]

I run the quickfuel 830, it was way rich on the idle circuit out of the box. I tuned mine with a wide band. I found that by reducing the IFR jets was considerably more effective than going up in IAB's. My carb came with .070" IAB's and I went to .078" to lean it out, while it had an effect I ended up going from .037" IFR's to .033" and .065" IAB's. Every combo will be different but I found the way to go with the idle circuit was with the IFR's and fine tune with the air bleeds.

[Nickrc3]

Justcruisin, thanks for your tips. I will be calling Proform tomorrow and listening to their suggestions as well. They've alluded to the fact that my issues may be resolved via the IAB's, so that was the direction I took.
I have read that the IFR's should be an area of focus.
Excellent article here: http://www.fordmuscleforums.com/all-ford-techboard/467850-need-proform-carb-help.html

Quite honestly, with my limited knowledge and no wideband analysis, I could be chasing this tuning thing for some time - not to mention purchasing full IAB/IFR/HSAB and main jetting kits. 

[NHCharger]

My update. First off- You can adjust that allen screw from the bottom. I noticed that as soon as I put the carb back on the engine so I put it back the way it was. Of course I have a fuel rail right in the way when trying to adjust it. To make it easier I taped a small screwdriver on the end of the allen wrench, much easier, was able to adjust while the car was running.

After adjusting the blades so the T-slots are square I started the car. Wouldn't stay running unless I had my foot in the gas, after cranking the allen screw up I was able to keep it running. Had the timing light and vacuum gauge hooked up so I could see the changes. Finally got it dialed in to a nice idle. I tried adjusting the four corner screws but like Nick I'm having a tunability issue. Turning any of them in or out seems to have no affect on the vacuum. On the link that Nick provided it recommends that you pick one screw, slowly turn it in until the rpm's drop, then back it off to the rpm's drop, then set it in the middle of that adjustment, then turn the other three screws to match that one. The problem I had was the rpm's keep increasing, even to the point of the screw being seated all the way in. At this point I just set all four at 1/2 turn out. The engine seems to be running good. 80% of the rich gassy exhaust smell is gone. I know my plugs are all fouled at this point so I'm waiting for that HF plug cleaner before I tweak on this again.
It's also hard to do a test drive with no fenders, hood or grille on the car.

[firefighter3931]

Justcruisin, thanks for your tips. I will be calling Proform tomorrow and listening to their suggestions as well. They've alluded to the fact that my issues may be resolved via the IAB's, so that was the direction I took.
I have read that the IFR's should be an area of focus.
Excellent article here: http://www.fordmuscleforums.com/all-ford-techboard/467850-need-proform-carb-help.html

Quite honestly, with my limited knowledge and no wideband analysis, I could be chasing this tuning thing for some time - not to mention purchasing full IAB/IFR/HSAB and main jetting kits. 

Nick,

reducing the IFR's is one way to go about it but that also requires some IAB adjusting as well. It's difficult to dial in w/o a wideband. 

I would try with some larger IAB's maybe one more time....then consider drilling the throttle blades. 

If you can get the idle circuit leaned out enough to achieve no richer than 13:1 AFR that should be good enough to keep the plugs clean, inmo.

Ron

[firefighter3931]

My update. First off- You can adjust that allen screw from the bottom. I noticed that as soon as I put the carb back on the engine so I put it back the way it was. Of course I have a fuel rail right in the way when trying to adjust it. To make it easier I taped a small screwdriver on the end of the allen wrench, much easier, was able to adjust while the car was running.

After adjusting the blades so the T-slots are square I started the car. Wouldn't stay running unless I had my foot in the gas, after cranking the allen screw up I was able to keep it running. Had the timing light and vacuum gauge hooked up so I could see the changes. Finally got it dialed in to a nice idle. I tried adjusting the four corner screws but like Nick I'm having a tunability issue. Turning any of them in or out seems to have no affect on the vacuum. On the link the Nick provided it recommends that you pick one screw, slowly turn it in until the rpm's drop, then back it off to the rpm's drop, then set it in the middle of that adjustment, then turn the other three screws to match that one. The problem I had was the rpm's keep increasing, even to the point of the screw being seated all the way in. At this point I just set all four at 1/2 turn out. The engine seems to be running good. 80% of the rich gassy exhaust smell is gone. I know my plugs are all fouled at this point so I'm waiting for that HF plug cleaner before I tweak on this again.
It's also hard to do a test drive with no fenders, hood or grille on the car.

That sounds good Brian 

You'll just have to see how the plugs look after they're cleaned up and re-run with the new idle mixture adjustments. 

Bigger then stock cams have more overlap and that in itself creates tuning headaches....in some cases you'll never completely eliminate the dirty idle but you can get it as good as possible with tuning. It's just the nature of the beast with modified engines. 


Ron

[justcruisin]

IMHO a wideband is worth the investment. If you have minimal experience with tuning it has infinite value. If like me you are not tuning carbs regularly, buying a selection of jets for IAB'S IFR's and mains can get costly. What I use is a set of micro drill bits, I use one set of jets to size things by drilling and soldering, preferably start out small and drill over size rather than solder and redrill. Once I have a tune I am happy with I simply order the jets I want. This works for me, I don't drill mains, mains are a little different as it is not only the hole size but the length of the hole that determines the flow, but drilling mains will get you in the ballpark. Just a tip, if you choose to do this make sure you don't get solder on the threads, you may damage your carb. Tuning with bleeds and restrictors really needs to be done in conjunction with a wideband, if you don't use one you will probably get in the ballpark but it will be an educated guess at best.

[NHCharger]

Bigger then stock cams have more overlap and that in itself creates tuning headaches....in some cases you'll never completely eliminate the dirty idle but you can get it as good as possible with tuning. It's just the nature of the beast with modified engines.  

Ron

Ron, you never told me it would be this fun  
The car actually moved under its own power today, first time in over three years. Just up and down the driveway. After the initial start up a couple weeks ago I had to adjust the secondary float-way to high. Primary was fine. When I pulled the car back into the shop I noticed the primary float was now way too high. I took the car back out up and down the driveway, still high. Why would it change like that??
Also the car will be idling beautifully, then suddenly change to a low idle and start stumbling. Revving the engine up will get it back to regular idle. Is this caused by the plugs being all fouled?

[firefighter3931]

Bigger then stock cams have more overlap and that in itself creates tuning headaches....in some cases you'll never completely eliminate the dirty idle but you can get it as good as possible with tuning. It's just the nature of the beast with modified engines. 

Ron

Ron, you never told me it would be this fun 
The car actually moved under its own power today, first time in over three years. Just up and down the driveway. After the initial start up a couple weeks ago I had to adjust the secondary float-way to high. Primary was fine. When I pulled the car back into the shop I noticed the primary float was now way too high. I took the car back out up a down the driveway, still high. Why would it change like that??
Also the car will be idling beautifully, then suddenly change to a low idle and start stumbling. Revving the engine up will get it back to regular idle. Is this caused by the plugs being all fouled?

What....you're not having fun yet ?   

Brian, do you have a fuel pressure guage on the dual feed inlet ? I'm thinking that your fuel pressure could be excessive and not allowing the float level to remain stable & excessive pressure will flood it at idle and drop the rpms down. When the idle drops like that take a look down the venturies and see if there is any fuel dripping from the boosters. There shouldn't be any. 

Fouled plugs will certainly make it run inconsistently 


Ron

[NHCharger]

Nope, no fuel pressure gauge, I'll pick one up tomorrow.
This morning I noticed after shutting the engine off while adjusting the idle that fuel was still dribbling out of the boosters for 15-30 seconds after shutting the engine off.

[BSB67]

This morning I noticed after shutting the engine off while adjusting the idle that fuel was still dribbling out of the boosters for 15-30 seconds after shutting the engine off.

There is your problem.

I would double check the simple stuff first.  The float level.

1) Take out both fuel level sight plugs. 
2) Lower the floats until the nut has little engagement with the needle valve assembly.  Fuel will spill out when you do this.  Mop it up.
3) Start the car with the plugs out. 
4) Let it warm up and turn up the idle if it helps to keep it running.  Bring the float up about a 1/4 turn at a time. Wait 30 seconds, do it again.  As you are doing this, nudge the fender of the car to cause the fuel to slosh back and forth.  When the fuel burps out of the hole...you're close.  Start making adjustments 1/8 turn at a time.
5) Stop when the level just get to the bottom of the hole.   
6) Do the same with the rear bowl.

Let the car run.  to see if the levels change.  If they hold, make your other carb idle tuning adjustments.

[firefighter3931]

Nope, no fuel pressure gauge, I'll pick one up tomorrow.
This morning I noticed after shutting the engine off while adjusting the idle that fuel was still dribbling out of the boosters for 15-30 seconds after shutting the engine off.

Ok, now we're getting somewhere ! Fuel dribbling is a sure sign that the floats are too high. Disconnect the fuel line to relieve pressure and readjust the float level(s) to 1/2 way up the sight glass. Get a non-liquid filled guage....the liquid filled ones don't read accurately once they get some heat soak. 

I'm guessing that your plugs are going to be pretty sooty/black so they will need a good cleaning. 


Ron

[NHCharger]

What should the fuel pressure be? The Carter fuel pump says it pushes 6-8 pounds.
Can I get a cheap in line regulator like this http://www.jegs.com/i/Mr.+Gasket/720/9710/10002/-1
Or spend the coin on something more fancy?

[Nickrc3]

What I use is a set of micro drill bits, I use one set of jets to size things by drilling and soldering, preferably start out small and drill over size rather than solder and redrill. Once I have a tune I am happy with I simply order the jets I want.

This is an excellent idea Justcruisin.  Thanks! I'm an old ET, so soldering is second nature. I'll be ordering me a set of the micro drills. JEGS sells the set for a reasonable price.

Firefighter3931 - yes, I have planned to continue the route with increasing the IAB's. Like you said, one more round of larger sizes and see what that does.

NHCharger, doesn't that vacuum gauge read fuel psi on the right side?

[NHCharger]

NHCharger, doesn't that vacuum gauge read fuel psi on the right side?

I think what Ron was looking for was an in line fuel pressure gauge/regulator. Just the gauge itself won't dial down the fuel pressure and keep it steady if that is whats needed.

[BSB67]

NHCharger, doesn't that vacuum gauge read fuel psi on the right side?

I think what Ron was looking for was an in line fuel pressure gauge/regulator. Just the gauge itself won't dial down the fuel pressure and keep it steady if that is whats needed.

Why would you presume that you need a regulator?  Literally hundreds of thousands of those pumps are sold to street guys without the use of a regulator.

[NHCharger]

If the fuel pressure gauge shows the fuel pressure too high or irregular how will I be able to regulate it?

[BSB67]

If the fuel pressure gauge shows the fuel pressure too high or irregular how will I be able to regulate it?

Again.  That pump is not intended to use a regulator. 

A gauge is normally used to check if there is enough fuel pressure at WOT, and if not, get a higher output pump.

True race pumps often have a high pressure output that require a regulator to reduce pressure just before the car.

You could start by purchasing a gauge, regulator, and installing it all. And then adjust your floats.

Or, you could buy a gauge and check to see if there is some kind of a manufacturing defect that is causing the pump (i.e. the spring) to generate too much pressure. Then buy a new pump ( my choice) or buy a regulator.  And then adjust your floats.

Or you could adjust and double check your float levels.

Your call.

[NHCharger]

Finally had some time to play with the carb. Following Nick's lead I bought some .78 IAB's from Jeg's along with a spark plug cleaner. Removed the carb, checked the T-slots. The secondary was too exposed again but I expected that. I adjusted the T-slot, installed the new IAB's and a fuel pressure gauge on the fuel line. Also lowered both floats, figure I'd start from scratch. Cleaned all the plugs (#3 was a joy to access).
After starting the car I adjusted the floats, had to open up the secondary blades a bit, float levels seemed good, then seemed to drop, car had trouble idling- was running out of fuel . After dumping five gallons in the tank the car ran much better. I set all four corner idle screws at one turn out. I tried adjusting from there but the car seemed pretty happy with that. Still have a little bit of the dirty exhaust smell and the idle has a bit of the bump in it. Vacuum is reading 13 lbs. It starts right up when hot without any fuss. I'll pull a few plugs when it cools down and take a look. Fuel pressure was 5-6 lbs. at idle.

[stuubi]

-Fuel press seems to be ok,
-On regular street car,fuel level can be at the bottom of inspection hole.It's still enouf for basic driving and melting tires.
-you could give less fuel on secondary idle circuit,like 1/4 to 1/2 turn.I've seen that engines with moderate cams,DB carbs can have good idle mixture this way.And i use wideband.
-Removing 1 size on airbleed equals 2-3 size on main jet's..So even 1 size adjustment should be noticed.But on idle circuit,2-3(Like Ron said) sizes should throw mixture so it can be notised.
-Also don't forget powervalve..

Never open secondary blades too much.Take carb of,set blades to trasfer slots,and do everything you can without touching sec blades.
This could cause your "black smoke"?

[BSB67]

-Removing 1 size on airbleed equals 2-3 size on main jet's..

Think that is backwards.

[NHCharger]

Never open secondary blades too much.Take carb of,set blades to trasfer slots,and do everything you can without touching sec blades.
This could cause your "black smoke"?

Never had black smoke. Just a raw exhaust smell that would make your eyes bleed and choke you. 90% of that is gone. Will pull the plugs tomorrow and inspect.
I only turned the allen screw adjustment for the secondary blades a half turn at the most. Now that I seem to have the carb somewhat dialed in I will back it off and see if I can adjust the idle with the four corner screws.
Appreciate the input  from all of you.

[firefighter3931]

Good work Brian....you're creeping up on it 

The fuel pressure guage was a good addition ; now we know excessive fuel pressure is not an issue 

Keep monitoring the vacuum guage as you tune the 4 corner idle mixture screws. As soon as it reaches max vacuum move on to the next one.

Keep us posted on your progress



Ron

[1970Moparmann]

Keep monitoring the vacuum guage as you tune the 4 corner idle mixture screws. As soon as it reaches max vacuum move on to the next one.

Ron, is this a repeated process after all four screws have max vacuum?  Special sequence?

Thanks!

[firefighter3931]

Keep monitoring the vacuum guage as you tune the 4 corner idle mixture screws. As soon as it reaches max vacuum move on to the next one.

Ron, is this a repeated process after all four screws have max vacuum?  Special sequence?

Thanks!

Hey Mike,

I like to start at the driver front and work my way around the carb going counterclockwise. You might have to go around twice to get it dialed in just right. Start with the screw 1 turn out from bottom and go from there. 


Ron

[stuubi]

-Removing 1 size on airbleed equals 2-3 size on main jet's..

Think that is backwards.

1 size smaller air bleed equals 2-3 bigger main jet's.

More than 4-5 sizes of jet and i will like to change air bleed instead.

Never open secondary blades too much.Take carb of,set blades to trasfer slots,and do everything you can without touching sec blades.
This could cause your "black smoke"?

Never had black smoke. Just a raw exhaust smell that would make your eyes bleed and choke you. 90% of that is gone. Will pull the plugs tomorrow and inspect.
I only turned the allen screw adjustment for the secondary blades a half turn at the most. Now that I seem to have the carb somewhat dialed in I will back it off and see if I can adjust the idle with the four corner screws.
Appreciate the input  from all of you.

Ok,term "black smoke" was just what i meant.Sorry for my bad typo(From Europe)
Half turn will open blades pretty much,take a look how much linkage is moving,or better yet,take a flashligt and see from the blades directly.
And get a wideband,it will take a lot of guess work away.
You'l see that even tiny 1/4 turn on idle mix WILL make difference in AFR.
And remember that idle mix screw's will affect AFR at low engine speed's also..

Do you have checked power valve?How much vacuum do you have at idle with gear?

[BSB67]

-Removing 1 size on airbleed equals 2-3 size on main jet's..

Think that is backwards.

1 size smaller air bleed equals 2-3 bigger main jet's.

More than 4-5 sizes of jet and i will like to change air bleed instead.

I still don't believe that is correct.  Air bleeds are for fine tuning, and also effects fuel curve, and responsiveness of the circuit.

[stuubi]

That what you said is correct in my opinion,it will alter fuel curve on specific area.
But still i've seen big changes on air bleed's,even on idle.

And on wot test,if you have good AFR but lousy rich on idle,intermediate,in my opinion it's better to change air bleed's than swap jets.

And on that scenario,if you would like to affect on "rich" point's,you would have to decrease 2-4 sizez of main jet to get it on the sweep spot.But give little risk on running lean on WOT.
So 1 or 2 sizez of air bleed will bring it down,but still keep wot at good number's.

And if intermediate is overly rich,it will have small affect on high speed also.Plus it will ruin your 60ft or 660ft times most likely.
and have car feeling sluggish,bleeding eyes etc.

Like i said earlier,my typing is not good as my thinking.I'm not from states.
That's what i mean't on air bleed vs main jet-comment.I was more tuning the curve than moving the whole curve.
I thought that proplem was in the curve,not the whole curve.

Sorry for the mis understanding i caused

[BSB67]

I'm having technical issues (self induced) on my last couple of posts..

On the subject of air bleeds, I think we'll just need to disagree.

[justcruisin]

I can't see how changing mains will have an effect on idle AFR as all the fuel will be through the IFR jets. As far as WOT is concerned I get my idle cruise an moderate throttle right and tune WOT with secondaries, power valve and PVCR jets. Although I am tuning for the street and not the track. I agree with BSB67 on the air bleed effect. I guess there is more than one way to get the job done and we all do what works for us, good discussion though.

[NHCharger]

Still playing with the carb. I have actually driven the car about 16 miles. After a 12 mile run on Sunday I pulled three plugs (easiest ones to access). They look a little too white?? Not the greatest at reading plugs but I thought they show it running lean. Currently all four corner idle screws are set at 3/4 turn out. I reset them all at 1 complete turn out and went for a 3 mile drive. The idle speed dropped a bit after the adjustment and I could notice a stronger gassy smell when I pulled into the shop and let it idle for a moment.The car ran fine but with only 16 mile on the engine I'm still babying it.

Below are two pics of the plugs, front left to right, # 8,2,1.
tomorrow night I will pull the same plugs and also check the timing.

[firefighter3931]

Still playing with the carb. I have actually driven the car about 16 miles. After a 12 mile run on Sunday I pulled three plugs (easiest ones to access). They look a little too white?? Not the greatest at reading plugs but I thought they show it running lean. Currently all four corner idle screws are set at 3/4 turn out. I reset them all at 1 complete turn out and went for a 3 mile drive. The idle speed dropped a bit after the adjustment and I could notice a stronger gassy smell when I pulled into the shop and let it idle for a moment.The car ran fine but with only 16 mile on the engine I'm still babying it.

Below are two pics of the plugs, front left to right, # 8,2,1.
tomorrow night I will pull the same plugs and also check the timing.

Brian,

The idle dropped when you richened the mixture....that makes sense and shows that the idle circuit is now functional/responsive.  I would go back the 3/4 turn to eliminate the rich idle which will keep the plugs clean. Under no-load conditions it's OK to be lean. Idle AFR of 14-14.5:1 is fine.

Take it out for a 20 min run and keep the rpms steady at say 2000-2500 rpm then shut down right away and pull a plug. Don't let it idle at all. This should give you an accurate cruise (light load) reading on the plugs. 


We can revisit the wide open jetting once you get some more break-in miles on the engine 

Looking at the plugs it doesn't look too lean to me. 



Ron

[NHCharger]

Ron, Plugs after todays cruise. (Thursday nights cruise did not end well )I live on a dirt road so there is 2-3 minutes of engine idle driving until i get from the paved road to my shop.
The plugs from L to R  1-2-4-5.  They still look a little too white compared to my other cars. Would it help if I backed the timing down a couple degrees?

[firefighter3931]

Ron, Plugs after todays cruise. (Thursday nights cruise did not end well )I live on a dirt road so there is 2-3 minutes of engine idle driving until i get from the paved road to my shop.
The plugs from L to R  1-2-4-5.  They still look a little too white compared to my other cars. Would it help if I backed the timing down a couple degrees?

Brian, try richening up the idle mixture a small amount. It doesn't take much so go slowly....maybe 1/4 turn at a time 


Ron

[ottawamerc]

Nh that's how my plugs look too and according to my A/F gauge I'm running a little rich

Scott

[Nickrc3]

Firefighter3931 - yes, I have planned to continue the route with increasing the IAB's. Like you said, one more round of larger sizes and see what that does.

Well, I installed new #78 IAB's - no difference. Engine still runs best with the idle-mixture screws 1/2 turn from base. Plugs were pulled and though not clean, definitely not carboned-over & sooty. Exhaust smell has improved.
I'm now at the point where I feel generally satisfied with the results, therefore, may leave well-enough alone. She start good, idle is @ 835RPM, and has very impressive acceleration. Drilling the primary throttle blades is my next option, however, my focus is now switching over to my teenage car:



circa-1977. Those side window stickers were worth another 15HP 

Starting a new thread over in the body forum

[BSB67]

Firefighter3931 - yes, I have planned to continue the route with increasing the IAB's. Like you said, one more round of larger sizes and see what that does.

Well, I installed new #78 IAB's - no difference. Engine still runs best with the idle-mixture screws 1/2 turn from base. Plugs were pulled and though not clean, definitely not carboned-over & sooty. Exhaust smell has improved.
I'm now at the point where I feel generally satisfied with the results, therefore, may leave well-enough alone. She start good, idle is @ 835RPM, and has very impressive acceleration. Drilling the primary throttle blades is my next option, however, my focus is now switching over to my teenage car:



circa-1977. Those side window stickers were worth another 15HP 

Starting a new thread over in the body forum

Or you could do what was suggested on the second post of this thread and likely actually fix the problem.   

[Nickrc3]

BSB67,
          Yes, I suppose reducing those four IFR's would be the next logical choice. Their size is not specified on the 750DP spec card. Does anyone know what size may be installed on this particular carburetor? I had the fuel bowls off the carb this weekend, but never bothered to observe their size.

Thanks Guys!