Tuning a Proform/Holley carb, what parts and tools?

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Patience? No problem. Been there. :)

If the gage isn't trustworthy, go by the fuel level in the bowls. Getting the level stable is really important. If the level is rising the bowls, then maybe it really is getting to 8psi because that's higher than most needle and seats can tolerate. I had a problems with fuel delivery for quite some time and switching to a pump (mechanical) that was capable of exceeding 7psi when letting off the throttle or idling caused flooding at the most inconvenient times. Of course I didn't realize this at first. I have pressure gage that mounts on the cowl but don't leave it on for every day use as its not waterproof. Took me several years before I put the common factors together and realized it was the pump.

In your case, if the level is not stable then with a regulator and I assume an electric pump, its probably the regulator or vapor. If there's an inline filter, having the outlet higher than the inlet so the vapor escape. Took me a long time 'discover' this little detail of factory engineering. Discover meaning a sentence in some book setting off a light bulb, not some great discovery!
 
Punp is a Carter M6902 mechanical.

https://m.summitracing.com/parts/crt-m6902

Other than a little sloshing from the car rocking side to side with the cam lope, fuel level looks very stable at idle.

I keep wondering how to route a fuel pressure guage , even temporarily, that I could have someone watch at WOT?
 
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That pump number used to be fine without a regulator, but I've noticed a number of posts here and at moparts where people are complaining about the cutoff pressure being higher since they started producing them again.
When we tested the Competition version, it's regulating spring resulted in 7.5 psi cutoff (which is why I was having occassional flooding problems). Of course having the filter perfectly flat didn't help.
Mechanical Fuel Delivery for Mopar LA Engines

As long fuel level is holding steady at least you can tinker with the tuning. It will be valid as long as the fuel is at that level.

I'll probably start a new thread on pressure gage setups when I get some pictures. I made my setup long before digital camaras. Mine was direct to a mechanical gage, which is why it gets mounted outside. Also easy to see on the cowl. To do this bent brake hard line to slip between the hood and the cowl. Easy to scratch up the paint doing this so it may not be for everyone. -3 AN hose connects the hardline to a T on the feed lines at the carb. An AN cap replaces it when not in use.

OTH, almost any pump is capable of keeping up. I was having problems with a Holley chrome pump, probably not even made anymore, AND what must have been problems in the original supply line where it went over the axle. There was a small rust spot there near the exhaust pipe. At the strip pressure would drop to zero, and it still had enough fuel in the bowls to make it through the quarter. MPH and time was a little off but not much. I could hear it too. Point here is don't sweat the pump's capacity. Do watch the max pressure. The Carter 'competition' pump helped but did not solve the problem (which was the line) and it created a new problem with its 7.5 pressure rating. Going over pressure is the worst when hot or when lifting from 3000 rpm because at the speed the pump is delivering much more fuel than at 900 rpm. (There's a link on my webpage to an explanation of how mechanical pumps regulate.)
 
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KnuckleDuster said:
Now set to about 7/8 of a turn out, and adjusted idle screw from all the way out. Idles about 900 rpm in park and 825 in gear.
Tired tonight but will get a vacuum guage and a helper tomorrow to set in drive.
Click to expand...
Focus on this today. It should be less frustrating. Big accomplishment will be getting it so you can drive to work and around town without blackening the spark plugs.
See what it takes with the mix screws to get that best vacuum once warmed up.

Then, if you're up for it, see what effect timing has. With the current 75 rpm drop timing and throttle position are probably pretty close to being on the money. So this is would really be an experiment for your own learning.

Do this by adding 2 degrees to the base timing, reset the rpm down to 825 in D or 900 in N (because the only change wanted is the timing and throttle position, idle rpm needs to stay the same) . Then readjust the mix screws. This should change the Neutral to Drive rpm drop. It may also change the low speed driving characteristics. So take it for a put-put drive around the block and note any change. If no change to either, then its right in a good spot for initial timing. If it the rpm drop going into gear reduces, the the higher initial is probably better. If it flat spots when gently accelerating from a stop sign or say from 30 to 45 mph, then the primary idle circuit is now too lean or too much timing adding in as the rp climbs. Doubt that's going to happen, but if it does, go back to the previous setup. If it gets sluggish, then its too rich; again, doubt that's going to happen, but this is a test to learn. If I had the magic bullet I'd tell ya! But there isn't any. This is just a test to see the effect of increased timing which should allow a slightly more closed primary throttle position.

If you're not up for it today, that's fine too.
 
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Timing right now is 19/33 in by 3k, no vac adv hooked up yet, just FYI...

Also, I noticed while checking the t-port the slots are elongated even with the idle screw backed all the way out. Does that suggest the throttle blades are clocked wrong or not closing all the way? They looked parallel to the base...
I' m going to have to pull the carb again and go back over it. Probably tomorrow afternoon as there is a good local show in the morning I don't want to miss.
 
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KnuckleDuster said:
Also, I noticed while checking the t-port the slots are elongated even with the idle screw backed all the way out. Does that suggest the throttle blades are clocked wrong or not closing all the way?
Click to expand...

Yes it does. Also check the fast-idle and choke linkage to make sure they are not keeping the throttles from closing completely.
 
It's hard to state definatively what is correct with many of these new carbs because the transfer slots are often longer and/or wider than the old school Holleys. About .020 to .040" or square looking should still be ballpark, but go with what works.
Longer and wider, all other things being equal, means that at idle more air bleeds in the top and as the throttle opens the ratio of air bleeding in the top to fuel out the bottom changes to richer quicker than a narrower shorter slot.

When you feel like doing some reading:
Transfer Slot Length? where the length is directly reduced using a set screw in base plate.

More commonly if the slots are too wide or long (ie causing tuning problems) a restrictor is placed in the transfer slot feed. This helps lean out the low throttle above idle. Nailing the exact size is a matter of testing. The fuel at this point already has air bled into it so it can be very sensitive.
A couple of examples:
Carb Help
Holley 870 Avenger Converted to 4 Corner Idle
Just so you know that success will eventually be attained. :)
Proform 850 Race Carb Update!!
 
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Mattax said:
That pump number used to be fine without a regulator, but I've noticed a number of posts here and at moparts where people are complaining about the cutoff pressure being higher since they started producing them again.
When we tested the Competition version, it's regulating spring resulted in 7.5 psi cutoff (which is why I was having occassional flooding problems). Of course having the filter perfectly flat didn't help.
Mechanical Fuel Delivery for Mopar LA Engines

As long fuel level is holding steady at least you can tinker with the tuning. It will be valid as long as the fuel is at that level.

I'll probably start a new thread on pressure gage setups when I get some pictures. I made my setup long before digital camaras. Mine was direct to a mechanical gage, which is why it gets mounted outside. Also easy to see on the cowl. To do this bent brake hard line to slip between the hood and the cowl. Easy to scratch up the paint doing this so it may not be for everyone. -3 AN hose connects the hardline to a T on the feed lines at the carb. An AN cap replaces it when not in use.

OTH, almost any pump is capable of keeping up. I was having problems with a Holley chrome pump, probably not even made anymore, AND what must have been problems in the original supply line where it went over the axle. There was a small rust spot there near the exhaust pipe. At the strip pressure would drop to zero, and it still had enough fuel in the bowls to make it through the quarter. MPH and time was a little off but not much. I could hear it too. Point here is don't sweat the pump's capacity. Do watch the max pressure. The Carter 'competition' pump helped but did not solve the problem (which was the line) and it created a new problem with its 7.5 pressure rating. Going over pressure is the worst when hot or when lifting from 3000 rpm because at the speed the pump is delivering much more fuel than at 900 rpm. (There's a link on my webpage to an explanation of how mechanical pumps regulate.)
Click to expand...

Mine read 8.5psi on my guage when it is cool.
I suspected as much after searching posts on similar issues.

Can you or Yellow Rose please post a link to the micro drill bits you use?
 
This is the set of 80-61 drill bits I bought:
McMaster-Carr
This will cover the holes smaller than your standard numbered drill set.
61 is .0390" diameter, IFR's and e-holes will be smaller than that.
75 is .0210" diameter, and that's normally smaller than anything I can think of, maybe if your using 3 emulsion holes instead of 2.

Usually its best to hold the drill bit still and put the set screw in the drill chuck.
But this pin vise can be held in the drill chuck as well.
McMaster-Carr
I might have bought at least one of mine from ENCO or MSC Direct.
McMaster-Carr is convenient and fast, not always cheap.
ENCO has a lot of overseas stuff, but they also are more focused on tools for the machinest.

If you're just using the bits to measure diameter, then you can skip the pin vise.

Model railroaders and such are another user group for tiny drills, so if there is a hobby shop near you, they might carry them.

Your Proform main body and blocks will likely already have some things tapped and a selection of restrictors can be purchased. But if not, below is a thread on tapping and installing drilled set screws. any of the industrial supply places above (or locally) will have the tapps. I can't recall whether I bought mine locally, or from McMaster or Enco. The set screws almost certainly came from McMasters.
http://racingfuelsystems.myfunforum.org/viewtopic.php?f=25&t=121
 
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Been messing with the carb for four hours...still running like ****.

I don't get why the ran better than ever the first day, then started fouling plugs and stuttering. If I get on it hard, it wants to die afterwards.
Pulled NGK FR4 plugs again and they were all black. Cleaned with brake cleaner, copper wire brush, and shop towels and reinstalled.Was just trying to get it to run good enough to go to the show, but not sure I'm even going now.

If I rev it fast a couple times at idle in park, fuel comes out the bowl vents.. Pulled my air cleaner to find the base full of fuel...WTF? The onlly things I have messed with are the choke, four idle screws, main idle screw, and float levels.
Float levels are a hair above middle in the window and steady.
Mixture screws are five eights of a full turn out from seated.
Idle screw is three turns in from contact with the arm.
Choke is on fifth notch from center CCW.
 
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KnuckleDuster said:
If I rev it fast a couple times at idle in park, fuel comes out the bowl vents.. Pulled my air cleaner to find the base full of fuel...WTF?
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Well there's only one way for fuel to be coming out the vents.
Right?
The bowls are overfilling as the engine speeds up.
So what controls that?
Primarily its the float and needle and seat.
But when there's is too much pressure in the feed lines, the needle can get pushed off the seat.

Since this only happens when the engine speed increases, it would seem most likely that the pump is the root cause. We know this pump has an internal regulation spring that has too high a cutoff pressure. So it comes down to the external pressure regulator. It appears to be allowing the pressure to climb as the pump's output volumetric output increases.

Hopefully its something about the way this regulator is set and can be made to work. See what the instructions say. Try setting it down around 4.5-5 psi at idle. I can't be specific here. I bought a regulator but ended up never using it.

Feel free to check out the float system too. The fact that you can adjust it to different levels (at 900 rpm) just suggests that its not hanging up or has some other issue that keeps it from working.
 
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Mattax said:
Well there's only one way for fuel to be coming out the vents.
Right?
The bowls are overfilling as the engine speeds up.
So what controls that?
Primarily its the float and needle and seat.
But when there's is too much pressure in the feed lines, the needle can get pushed off the seat.

Since this only happens when the engine speed increases, it would seem most likely that the pump is the root cause. We know this pump has an internal regulation spring that has too high a cutoff pressure. So it comes down to the external pressure regulator. It appears to be allowing the pressure to climb as the pump's output volumetric output increases.

Hopefully its something about the way this regulator is set and can be made to work. See what the instructions say. Try setting it down around 4.5-5 psi at idle. I can't be specific here. I bought a regulator but ended up never using it.

Feel free to check out the float system too. The fact that you can adjust it to different levels (at 900 rpm) just suggests that its not hanging up or has some other issue that keeps it from working.
Click to expand...

Yeah, ok, that makes sense. I forgot about jacking around with the regulator. I should have no faith in the cheap Mr Gasket FP guage... I have read most guages go funky as soon as they get warm, does anybody kbow of a reliable replacement?
By the guage I only increased the pressure by .5 psi. The regulator is such a simple piece. I would suspect the guage before the regulator.
Thank Mattax!
I need to stop making more than one change at a time! I get impatient when I get frustrated, sorry....but thanks for taking the time to walk me through this.
 
I'm guessing that the regulator can't bleed off extra pressure. That would make it hard to judge the adjustment in one direction, probably in reducing the pressure. See if the directions have anything about this. Also, depending on how its designed the pressure regulation may be plus or minus some amount. Lets say baseline went from 5.5 to 6 andlet say the plus minus is 1 psi. 5.5 + 1 = 6.5 which is just OK and may have been only an occassional problem, but set at 6 it easily goes to 7 psi.

As far as the gage, this is first I've heard of one being temperature dependent. How quickly they react (damping) is a more typical concern. Most are just a closed tube and some fine springs and movements. Somewhat fragile yes. When they fail, its usually consistant (doesn't return to zero or whatever) so I'm not help on this one. I can't even think of a reason why a mechanical gage would be so temperature dependent to be off by 25%
 
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I have read any liquid filled FP guage is sensitive to high temps.
My cheapo Mr Gasket is only accurate at room temperature.
 
KnuckleDuster said:
I have read any liquid filled FP guage is sensitive to high temps.
My cheapo Mr Gasket is only accurate at room temperature.
Click to expand...

Most good liquid filled gauges have a vent on top that you can crack to equalize the internal pressure with ambient. If you do that before taking a reading, they're pretty accurate IMO. This is a good one- noticed the vent on top. Plus, Summit will price match the ebay prices of $32 with free shipping.

https://www.summitracing.com/parts/aei-15632
 
Didn't make it to the show, cranked fuel pressure back to 4psi on the guage. Went and bought a new air filter, and the carb soaked it in gas the first mile.
Had to take it off just to get home.
Really starting to get pissed with this carb!!!
Trash in the needle and seat?
Floats too high? (just above middle, but lower tha they were out of the box)
Faulty psi guage?
Filled the tank with $25 worth of fresh gas.
Lines don't feel hot, would say maybe the carb is getting hot if it hadn't run fine before...
I probably jacked something up, but too frustrated to mess with it anymore today!
Gonna pull the carb off tomorrow and disassemble it.
Don't think iI blew the PV because the mixture screws are still responsive, but I wiil swap a new one in tomorrow, anyway, card says it has a 6.5 in it. I only get about 9" of vacuum with this cam, which PV should I try? Could the 6.5 be part of my problem?
Any other tips on what to look for that hasn't been mentioned?
 
Didn't make it to the show, cranked fuel pressure back to 4psi on the guage. Went and bought a new air filter, and the carb soaked it in gas the first mile.
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Well that sucks, or rather blows. Several times I had to bleed off fuel from the bowls on the side of the highway.
Trash in the needle and seat?
Floats too high? (just above middle, but lower tha they were out of the box)
Click to expand...
One of these or the regulator. Remember there's no pressure in the bowl (well atmosphere but you know what I mean). Can't be the gage other than possibly misleading you on the regulator setting. For some reason the fuel level by the sight glass looks right at idle and is overfilling with only what? a few hundred or 1000 rpm increase.


Don't think iI blew the PV because the mixture screws are still responsive, but I wiil swap a new one in tomorrow, anyway, card says it has a 6.5 in it. I only get about 9" of vacuum with this cam, which PV should I try? Could the 6.5 be part of my problem?
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In reverse order:
No. Even with no power valve, it would be bleeding fuel into the base of the carb direct to the intake. Only way its coming through the bowl vent is overfilling. It's probably pouring out the main boosters as well.

I mean I guess if there was no squirters on the accelerator pump passage it would squirt up into the air cleaner but that's grasping at ideas when it seems like you've seen exactly what is happening. Why is the question.

I've limped my wagon back to my garage using gravity feed for fuel to bowls. That's all it takes to keep a carb bowl full at low throttle. So there's a possible test since you had it blow out the vent just revving it in the driveway. You'll have to get a little siphon action going. Butif you do this, obviously take your time on the setup and BE CAREFUL.

Power valve selection. Opening simply adds another path for fuel into to the main system. The idle system picks up fuel from the main. The idle restrictions are (normally) much smaller than the main restrictions so flow in the idle system is not normally effected by the power valve being open or closed.

Power valve opening point will be something less than cruising vacuum. Cruising here meaning being interstate speeds. My current setup cruises around 17-18"Hg so I'll use that as an example. Opening the throttle a bit drops the vacuum. If it accelerates well at 12"Hg but starts to flatten out at 10", then a 10.5" PV would be appropriate. If it doesn't flatten out until 6", then a 10.5 would probably make it more sluggish when part throttling from 7-10"Hg. In the Holley Carburetor and Manifolds book there is a section on testing this by 'crowding' a vacuum. This sort of trial and error testing is about the best most of us can do.
 
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If fuel is coming out of the vents, it's only three possible things.
1. Float level too high.
2. Float is junk.
3. Needle and seat is junk.

That's it. A blown power valve will make it hard to hot start and make it act like its flooded. As long as you set the power valve opening by CRUISE vacuum and NOT idle vacuum you'll be ok. Probably and 8.5 is a good starting point. A bigger number power valve has zero affect on idle and hot start fuel. A blown PV will.

Damn, I just thought of a 4th. Could be dirt in the system. That would be needle and seat related of course.

That's is. There's not much to it. If fuel is just coming out of the booster, that is a float adjustment or bad float.
 
KnuckleDuster said:
Sorry Mattax, still too pissed off to go near it today!
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Appreciate the update.

Yellow Rose. All true. Definately should be checked out.
But also if pressure in the feed line for any reason goes up, at some point it will exceed the force of the float holding the needle closed. This problem is worse with larger inlet valves as they have a larger area. Force = Pressure x Area
If it turns out that its not carb's system, then its worth doing whatever it takes to see if its the pump and regulator. I hate to suggest buying anything new when possibly not needed, but one way to test it out is swapping in a pump with internal regulation at 6psi or less and eliminating the regulator. A stock type pump would be fine for just seeing what's going on. Maybe borrow a used one or parts store.
 
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Mattax said:
Appreciate the update.

Yellow Rose. All true. Definately should be checked out.
But also if pressure in the feed line for any reason goes up, at some point it will exceed the force of the float holding the needle closed. This problem is worse with larger inlet valves as they have a larger area. Force = Pressure x Area
If it turns out that its not carb's system, then its worth doing whatever it takes to see if its the pump and regulator. I hate to suggest buying anything new when possibly not needed, but one way to test it out is swapping in a pump with internal regulation at 6psi or less and eliminating the regulator. A stock type pump would be fine for just seeing what's going on. Maybe borrow a used one or parts store.
Click to expand...


I didn't mention fuel pressure as I though the OP ruled that out but yes, fuel pressure will push fuel out the vents.

I have a gauge on my car that says 10 PSI but I know it isn't that high, or it would blow fuel past the needle and seat. So I need to get a verified gauge and see what the issue is.
 
Ok guys, before I go into everything else I found wrong, answer me this-

Why am I seeing bubbles in the front fuel window at 3000rpm?

Back one is clear and the level doesn't move.
 
Probably
a. Primary bowl is supplying almost all of the air/fuel to the engine.
b. What you are seeing is probably due to pressure at high flow.

See the video link Mark Whitener posted here:
http://racingfuelsystems.myfunforum.org/viewtopic.php?f=25&t=741

Aeration impacts high Hp cars at the dragstrip and a number of people have been looking at it and ways to address it. More videos here.
Another solution to Fuel Bowl Aeration.
Last, a similar problem as you, and interestingly, also with a Carter mechanical pump.
Pump and Bowl Temperatures
 
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Wow just ran across this thread,couple of carbs later still problems with fuel pressure...put a gauge on it you got a vacuum gauge well that can be used to check fuel pressure....look at it ,there is a pressure side...it ain't the dam carb so quit messing with it.
HOW ABOUT PUTTING A STOCK FUEL PUMP ON IT...To see how it runs,if you are too cheap to buy one because your broke,pull the one off of your truck...I know my advice means **** to you but I told this month's ago but it can't be the fuel pump....
 
Oh by the way carter fuel pump are easy to rebuild one diaphragm and three check valves...can take them apart and clean the thrash out of them....put a stock pump on it,,if you have problem on the top end it is to be expected but not at idle or cruise....
 
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