For the life of me i can't fix this damn lean problem im having with my carb. (list 80508-1) 750 square bore vac sec. My car idles at around 15" and 13;1 mixture. At steady low speed cruise it sits around 14 or 15" vacuum and around 13.5:1 ratio, now thats fine but the trouble begins under light load/acceleration. As vacuum drops the mixture leans.. by 10" its at around 15.5:1 and the car is jerking ect. (actually starts feeling too lean by 12" and is already playing up) This is all low rpms... around 1500rpm, i don't believe the main jets are in play yet and changing them doesn't help. I don't have a large cam and the transfer slots ect arn't uncovered at idle. Richening the idle doesn't seem to help either, it effects it but not enough to richen it out enoghh to stop the problem and then idle goes to hell anyway that rich. Is there any way i can stop it leaning out so fast as vacuum drops?
Holley flat spot/lean area
Mar 31, 2007
2 Replies
Have you tried replacing the power valve? I had a similiar problem with mine and it lead me to this valve on several occassions. I ended up scrapping the Holley and going with an Edelbrock and the problems never returned.
First, the Holley tunig manual would have a wealth of info for you. If this is happening as you describe just "crwoding" the throttle, I would suspect the fuel level is a bit low. At 1500 cruise, you are not quite high enough to be bringing in the secondaries just crowding the throttle. You may want to block the secondaries temporarily to see if this makes a difference. If it does, the secondaries are coming in too soon. A power valve with too low a setting will also cause this. Generally, I like a power valve about
2-2.5 below cruise level vacuum. If you are cruising at 14" with everything running, I would try a 10.5 or 11.0 The number is the vacuum at which the power valve begins to open. Most carb come out of the box with 7.5-9.0 IIRC. You can check the parts manual for you part # to see which it came with. You should also check to be sure you are not getting too much ignition advance too soon which can appear to have a leaning effect for the EG reader. You need to start with the fuel level and make sure fuel pressure is good. Low fuek pressure under load mau be caused by a restricted fuel supply like a clogged filter or a defective tank venting system.Good luck
Lugnut
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