Proform 750 CFM DP carburetor tuning?

[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