Holley Help!
Thread Starter
Racer
Joined: May 2006
Posts: 423
Likes: 3
From: New Port Richey, FL
Holley Help!
I just installed a 383 stroker in my 76. Motor has 9.7-1 comp, Comp Cams xs274s .507 lift 236/242 @ .050 solid lift cam, RPM intake, Holley 750 dbl pumper carb with annular boosters, Hooker Super Comp 13/4" headers, AFR 195 Eliminator heads. The problem is the car runs so rich that it burns my eyes out in the garage. The primary jets are 67, which are smaller than the carb came out of the factory with. I thought I may have blown the 6.5 power valve and replaced it , but still have the same problem. I checked the float levels removing the site screws and adjusting the fuel just to barely trickle out of these at idle, so thats good. I just installed a new MSD distributor and adjusted timing to 34 degrees all in @ 2800 rpm- still the same problem. I even ran fine wire down the air bleed holes to make sure they are clear. The lever on the primary pump diaphram has about .015" gap. How in the hell do I lean this thing out? Any advice would be greatly appreciated. I pulled the spark plug out of #1 and it's completely black. Thanks guys.
Race Director
Joined: May 2006
Posts: 18,740
Likes: 2,583
If you turn the primary bowl mixture screws completely clockwise till they bottom out does the engine stall out? Do you have the secondary throttle plate stop screw set for a 1/2 turn in from the secondary throttle plates being completely closed?
Thread Starter
Racer
Joined: May 2006
Posts: 423
Likes: 3
From: New Port Richey, FL
I called Sean Murphy at smi today. He said that a holley without annular boosters may use 1 1/2 turns as a starting point, but with the boosters start at 1/2 turn then put a vacuum guage on it and fine tune. I only went out 5/8 turn on the primary and 1/2 turn on the secondary. Boy what a difference! My eyes are no longer burning. Thanks
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
1: I think its running lean and burning your eyes.
2:Large overlap cams is always going to burn your eyes, if its lean at idle then its lean at wide open.
3: You need to drop to a at least 3.5 power valve.
2:Large overlap cams is always going to burn your eyes, if its lean at idle then its lean at wide open.
3: You need to drop to a at least 3.5 power valve.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Your stock PV is fine, you can even run a 8.5 PV, the low pv thing is imo backwards. Dont want it to open too soon
Start with your throttle plate adjustment, drop your floats just a tad and try it again.
67 Jet is on the lean side as a main. 68 min, Id start at 70 ft/80 rear
I dont use any clearance on the accel pumpdiaphragm some do. "Just touching"
Start with your throttle plate adjustment, drop your floats just a tad and try it again.
67 Jet is on the lean side as a main. 68 min, Id start at 70 ft/80 rear
I dont use any clearance on the accel pumpdiaphragm some do. "Just touching"
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Your stock PV is fine, you can even run a 8.5 PV, the low pv thing is imo backwards. Dont want it to open too soon
Start with your throttle plate adjustment, drop your floats just a tad and try it again.
67 Jet is on the lean side as a main. 68 min, Id start at 70 ft/80 rear
I dont use any clearance on the accel pumpdiaphragm some do. "Just touching"
Start with your throttle plate adjustment, drop your floats just a tad and try it again.
67 Jet is on the lean side as a main. 68 min, Id start at 70 ft/80 rear
I dont use any clearance on the accel pumpdiaphragm some do. "Just touching"
Here is something to look for if you have a Holley that idles rich and the idle mixture screws don't do much: Flip the carb over and make sure you are only showing about .020" of the transfer slot at idle. Use the idle speed screw to set this. Put it back on and fire it up. If you need to adjust the idle speed screw to get it running, keep track of how many turns you move it. Once it's running, open up the secondaries a little at a time, until you are able to screw the idle speed screw back to where it was. This way, the transfer slot is not overpowering the idle orifice in the throttle plate, and you'll have a nice, lean, crisp transition for good throttle response and economy at low speed cruise.
Scott
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
People need to run a low power valve so you have some rpms built before it opens.
Or if you take off and your vacuum drops faster than you gain rpms its going to run rich.
Drop your power valve to a 3.5 and this will eliminate the question of if you have the right one or not and you can move on to fixing something else.
Or just keep fighting to same ole problems everyday.
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Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Vacuum is what keeps it shut, if you have a 8.5 power valve and only 7lbs of vacuum at idle in gear then its going to open and be rich.
People need to run a low power valve so you have some rpms built before it opens.
Or if you take off and your vacuum drops faster than you gain rpms its going to run rich.
Drop your power valve to a 3.5 and this will eliminate the question of if you have the right one or not and you can move on to fixing something else.
Or just keep fighting to same ole problems everyday.
People need to run a low power valve so you have some rpms built before it opens.
Or if you take off and your vacuum drops faster than you gain rpms its going to run rich.
Drop your power valve to a 3.5 and this will eliminate the question of if you have the right one or not and you can move on to fixing something else.
Or just keep fighting to same ole problems everyday.
OK, when the power valve opens, it allows a little extra fuel to flow into the main circuit, thru the boosters. The throttle plates need to be opened up a little and some airflow going thru the venturis in order for this to come into play.The power valve isn't going to flood your engine with fuel at idle, no matter what the vacuum is. In theory, the open power valve will have an effect on the idle circuit, but it's just in theory, because it's such a small difference it's unmeasureable.Vacuum at cruise is what you need to be concerned with here. If your power valve opens at a vacuum level higher than the vacuum level that you cruise at, it'll run rich. If you try to make up for it by installing smaller jets, then you will go lean under load, a very bad situation which should be avoided at all costs.
If you hook up a vacuum gauge and run it into the cockpit, and start playing around with different power valves, you will soon get a "feel" for what the engine wants for a power valve. When I was a kid, a crusty old mechanic gave me the best carb tuning advice I have ever gotten. He said: "Son, ya gotta give the motor what IT needs.....not what YOU THINK it needs." Twenty years later, it's still good advice.
Scott
Last edited by scottyp99; Aug 18, 2011 at 04:05 PM.
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
scottyp99 is right on with his suggestion but I see you have already solved the problem.
I input is to help with the misunderstanding of the power valve circuit.
On a Holley the idle and transition circuit are feeding the fuel up to about 2600 rpm's. The primary main jet don't start until than. It takes enough air flow through the carb to pull the fuel up to the boosters, until that flow is reached the fuel being supplied is coming from the transition circuit.
The power valve feeds into the main well, the carb has to be pulling fuel from the main circuit before the power valve will have any effect. At low rpm's you will not see the effects of the power valve unless the diaphragm is ruptured or the gasket if broke but than you would have an idle mixture issue also.
an annular booster carb will either have larger main air bleeds or smaller main jets to compensate for the increased vacuum signal created by the booster. The problem with larger main air bleeds is they will reduce the sensitivity of the main circuit and the enrichment circuit may not be able to keep up with demand if the carb that's tuned for 14:1 AFR at cruise.
Neal
I input is to help with the misunderstanding of the power valve circuit.
On a Holley the idle and transition circuit are feeding the fuel up to about 2600 rpm's. The primary main jet don't start until than. It takes enough air flow through the carb to pull the fuel up to the boosters, until that flow is reached the fuel being supplied is coming from the transition circuit.
The power valve feeds into the main well, the carb has to be pulling fuel from the main circuit before the power valve will have any effect. At low rpm's you will not see the effects of the power valve unless the diaphragm is ruptured or the gasket if broke but than you would have an idle mixture issue also.
an annular booster carb will either have larger main air bleeds or smaller main jets to compensate for the increased vacuum signal created by the booster. The problem with larger main air bleeds is they will reduce the sensitivity of the main circuit and the enrichment circuit may not be able to keep up with demand if the carb that's tuned for 14:1 AFR at cruise.
Neal
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Holley carburetors are so popular because of how simple they are to work on. I call 'em "Lego carbs"!! You can take 'em apart and see everything!!
All carbs pretty much work on the exact same principles, and if you have an understanding of how carburetors in general work, on a basic level, then you can take ANY carb, and work with it. If you have difficulty understanding how a Holley works, don't buy a book on how Holley's work, buy a book on how CARBS work. THEN buy a book on how Holley's work.
Scott
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
I was trying to help him understand how the enrichment system works on a Holley.
He resolved his issues so all is good and he has some good info on how the thing works.
Neal