HELP!!! too rich at idle

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wigsplitter74

wigsplitter74

The Mopar Kid
Joined
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Janesville, WI
I've just purchased a 6 month old 750cfm Proform double pumper carb for my duster, it's got billet metering blocks with 4 corner idle screws and a billet baseplate. This carb is sweet! My only problem is that it's way to rich at idle, so rich it smokes and reeks of fuel. My Idle mixture screws don't seem to do anything at all, in all the way or out all the way I don't see a change. I've driven the car on a straight stretch of road by my shop that happens to have some sticky prep on it and my car runs like never before, it's amazing. I have never been able to go WOT from a dead stop until this carb, if I can get the super rich idle fixed I'll finally have a good carb and get to see what this thing will really run. Please help me out!!!
 
check how much vac you have in gear and then check your power valve, fuel pressure, float level.
 
74Burntorange said:
check how much vac you have in gear and then check your power valve, fuel pressure, float level.
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At idle in park (I was alone) I have 15 inches of vacuum, the power valve is a 6.5 ( I tried an 8.5 also and now have a 7.5 for it) I have no clue on fuel pressure but it's a mechanical pump with stock fuel lines and tank. My float levels are dead on right at the very bottom of the hole.

I'm thinking about putting the carb back to box stock setup and starting from there, all my friends have EFI dammit, I'm too young LOL
 
hmm that sounds like a good idea, but take the vac reading in gear not park i have 13 at idle in park and 9-10 in D and i have to much richness so i need a 4.5PV
 
Just so I got this straight, will lowering the power valve lein it out? The carb came new with a 4.5pv in it which was changed and I don't have it, would too high of a PV cause the idle screws to not function properly? Thanks much, bare with me, I'm young and carbs are confusing
 
well the pv is what sends gas to the carb at idle. And I think a vac leak would cause them not to work.
 
how high is your motor ideling in park? it could be that you throttle blades are opened too much and if they are you can close them some and open the secondarys (back barrels) a little more, do you have removeable air bleeds? maybe try spraying carb cleaner into the air bleeds. the power valve wont or dont affect the idle mixture, while the motor is idleing can you see fuel dripping out of the boosters? how about the idle feed restricters do you know where they are and what size they maybe? these are suggestions to look at to diagnose your problem, one of the reasons your car is responsive is because of the richness but it needs to be leaned some so you dont foul the plugs, keep us posted on what you find.
 
i forgot to mention that if the mixture screws dont have any effect it is usually an indication that the butterflies are opened to far, so as i said recheck and adjust them, when its right you should be able to adjust the mixture screws to make a difference
 
??? the PV will make it rich at idle as it will pour more gas in if wrong size
 
74Burntorange said:
??? the PV will make it rich at idle as it will pour more gas in if wrong size
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The power valve shouldn't be doing anything at idle. This is the reason for turning the idle screws all the way in to check if it's blown. If it's intact, closing the fuel path across the idle screws cuts off the fuel source and if it keeps running, the fuel has to be coming from somewhere else. Its purpose is to add fuel when the engine is under a load (low vacuum).
 
how do you adjust the butterflies? and what casues the boosters to drip at idle or when the cars off?
 
check your float level running and remove the sight plug and set it so fuel just barely drips out. the float being set to the bottom of the sight plug doesn't mean its set ok, it has to be running to set the level properly. another thing to check that I learned from another member here (demon sizzler) is the initial timing set properly can play its part. I added a couple degrees and was able to adjust the speed and mixture screws and now mine runs fine.
 
doktor_x said:
The power valve shouldn't be doing anything at idle. This is the reason for turning the idle screws all the way in to check if it's blown. If it's intact, closing the fuel path across the idle screws cuts off the fuel source and if it keeps running, the fuel has to be coming from somewhere else. Its purpose is to add fuel when the engine is under a load (low vacuum).
Click to expand...

Dok is exactly right as to what the power valve should be doing.

74Burntorange said:
how do you adjust the butterflies? and what casues the boosters to drip at idle or when the cars off?
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On the underside of a stock style Holley carb there is a allen screw that can only be seen with the carb removed. Aftermarket throttle bodies put this screw on top for easy adjustment. First, you need to take of the fuel leaking from the boosters.

If you're dripping fuel from the booster/boosters at idle it can be quite a few things:

Floats not adusted correctly
Leaky needles & seats
Sunk floats
Too much fuel pressure
Carb boil over
Rust/dirt in the tank
 
In this statement ramchargere is talking about the secondary butterfly adjustment "On the underside of a stock style Holley carb there is a allen screw that can only be seen with the carb removed. Aftermarket throttle bodies put this screw on top for easy adjustment. First, you need to take of the fuel leaking from the boosters" useually when the mixture is way too rich on the idle circuit the secondary butterfly's need to be opened up.
 
wigsplitter74 said:
I've just purchased a 6 month old 750cfm Proform double pumper carb for my duster, it's got billet metering blocks with 4 corner idle screws and a billet baseplate. This carb is sweet! My only problem is that it's way to rich at idle, so rich it smokes and reeks of fuel. My Idle mixture screws don't seem to do anything at all, in all the way or out all the way I don't see a change. I've driven the car on a straight stretch of road by my shop that happens to have some sticky prep on it and my car runs like never before, it's amazing. I have never been able to go WOT from a dead stop until this carb, if I can get the super rich idle fixed I'll finally have a good carb and get to see what this thing will really run. Please help me out!!!
Click to expand...


I had the same carb and ran into the same issues you are describing. I also did everything all these great people here on FABO are suggesting and went as far as having a professional carb shop go over the cars and they installed it on another car where it worked just fine. What I ended up doing was to buy a 650cfm double pumper carb because it seems this 750cfm carb is just too much for my 360 engine. The down side is all the raw fuel that was not being burnt ended up washing down my cylinders and did some damage to my engine. I would suggest you do not run the engine to much until you decide what you are going to do.
 
This carb does have removable air bleeds and in park it idles right about 900rpm or so. If somebody could tell me more about the idle feed restrictors I would really appreciate it.
At idle the fuel is at the bottom of the sight plug on the fuel bowl. The only light I see through the secondary butterflies is from the little passages.
 
i would bet you need to change the air bleed to lean the idle circuit, i cant remember off hand withouy checking the book but the inner airbleeds i think are for the idle circuit and the outer air bleeds are for the wide open circuit it would be a easy fix but you need to make sure the air bleeds are clear and the remove them and see what size they are, for a quick fix you might try switching the air bleeds from inner to outer and start it and see what it does, idle feed restricters are what control the amount of fuel at idle but with the air bleeds i wouldnt worry about them nor what size they are cuz you can fix it by changing the air bleeds you will probably need to oder them from jegs or a carb shop such as C&S specialties or AED carburators they can also help you sort out your carb problems and get it right.
 
I have 750 Proform carbs and I like them. Ramcharger is right about what he said, based on my years of experience. The number of the power valve is the point at which it opens. For instance, a 6.5 power valve will remain CLOSED until vacuum drops to 6.5 inches of water. When the valve opens, it seriously enriches the fuel beyond what the main jets will flow. If the valve or gasket is bad, the valve will act like it is open all the time and get nasty rich. Another thing I have seen is when the gasket on the rear of the metering block is poor, fuel can leak to the back side and the engine sucks gas through the port in the throttle body that signals the power valve. The front side of the metering block should have a multitude of drilled and tapped holes. No brass restrictors should be in these. The carb will also go rich if someone fooled with the idle air bleeds. The idle bleeds are to the outside and the high speed bleeds are to the inside. See that they are not switched! The larger the orifice in the idle air bleed, the more air is pulled into the imulsion tubes/chambers of the jet block effectively leaning the mixture. Reducing the orifice does the opposite. My solid lifter 360 engine just loved that 750! Idle bleeds would be relatively correct with numbers 73 to 75. I used to convert a lot of carbs back in the day to four corner idle becausee the customer thought it was necessary or "cool" to have the mod. Personally, I've never seen a need for it at all. Now carbs have that nice idle screw on the top outside of the secondary shaft. Most people have no idea how to get idle quality with the 4-corner. I have never seen a big cam, low idle vacuum engine NOT respond to drilling a hole in the primary throttle blades to allow more air, thereby allowing the blade positions to be properly seated over the idle fuel transfer slots. Another thing...make sure there is no power valve in the secondary block. Use a plug. If you are trying to use that secondary idle, I think just maybe it is giving it too much. I sure hope this helps.
Pat
 
PFogel said:
I have 750 Proform carbs and I like them. Ramcharger is right about what he said, based on my years of experience. The number of the power valve is the point at which it opens. For instance, a 6.5 power valve will remain CLOSED until vacuum drops to 6.5 inches of water. When the valve opens, it seriously enriches the fuel beyond what the main jets will flow. If the valve or gasket is bad, the valve will act like it is open all the time and get nasty rich. Another thing I have seen is when the gasket on the rear of the metering block is poor, fuel can leak to the back side and the engine sucks gas through the port in the throttle body that signals the power valve. The front side of the metering block should have a multitude of drilled and tapped holes. No brass restrictors should be in these. The carb will also go rich if someone fooled with the idle air bleeds. The idle bleeds are to the outside and the high speed bleeds are to the inside. See that they are not switched! The larger the orifice in the idle air bleed, the more air is pulled into the imulsion tubes/chambers of the jet block effectively leaning the mixture. Reducing the orifice does the opposite. My solid lifter 360 engine just loved that 750! Idle bleeds would be relatively correct with numbers 73 to 75. I used to convert a lot of carbs back in the day to four corner idle becausee the customer thought it was necessary or "cool" to have the mod. Personally, I've never seen a need for it at all. Now carbs have that nice idle screw on the top outside of the secondary shaft. Most people have no idea how to get idle quality with the 4-corner. I have never seen a big cam, low idle vacuum engine NOT respond to drilling a hole in the primary throttle blades to allow more air, thereby allowing the blade positions to be properly seated over the idle fuel transfer slots. Another thing...make sure there is no power valve in the secondary block. Use a plug. If you are trying to use that secondary idle, I think just maybe it is giving it too much. I sure hope this helps.
Pat
Click to expand...


Pat,
Any tips for blow through carb.
KP
 
my carb had 72 all the way around and stil running rich with a 4.5pv whats wrong with my air bleeds?
 
900 is to high, you are not using the idle circuit.
Lower the curb stop until you have less than .040 of transfer slot showing under the throttle plate, drill holes in front of throttle plate, start at 1/16".
And increase the size until you have less than .040 showing. That uses the idle circuit.
 
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