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.