Forgive me for my questions, but needless to say I am not a engine guy. I am a super body man, and can bolt it together, but tuning is not my thing. I asked you folks before about jetting on my relatively stock 69 302Z. I had 66 in the front and 72 in the back. Idle was good but ran like crap. The consensus was that I needed bigger jets. I changed to 72 front and 76 rear as suggested. It seems that cured the running out problem, must have just been too lean. Now on occasion while blipping the throttle it backfires through the carb, but only on occasion. It also seems to be too rich when the secondaries come in as it spews black smoke. One gentlemen here said he had dynoed his engine and it ran best with 72 front, 66 rear jetting. What do you guys think? Should I go down in size? Leave it alone? Ideas? And by the way, I do appreciate your help. You folks have a wealth of knowledge and I sincerely thank you for sharing it. Maybe I can repay the favor someday by sharing some paint knowledge or something.

Thanks,

Ed

My stock Z is jetted 72/76, per Jerry MacNeish's recommendation, and runs great. Make sure you accelerator pump operating lever is properly adjusted - carb backfires are usually a symptom of a lean transition from idle to main circuit, which the accelerator pump covers.
graemlins/beers.gif

once you've checked the accelerator pump.. check your timing.. if its too far advanced it will pop up through the carb as well.

What is the preferred method to adust the accelerator pump on a 4150 holley?

helps to have 2 people,first person presses down hard on the accelerator pump arm with a flat bladed screwdriver near the adjusting assembly(bolt,nut,spring)but not touching it,and holds the throttle all the way open(engine off!).second person sets lash between pump arm and bolt head to .015".it can be done by yourself but it's way easier with a helper.
make sure arm is fully depressed and throttle is all the way open(this is the part the friend does smile.gif )
Eric

Thanks, that is a help. The only other method I had was with carb off the car.

The .015" is to keep the diaphram from being over streched and may not solve your problem. Start there first then if needed follow the arm to the primary throttle shaft where it rests on the cam that causes the pump to operate. Watch and see that the slightest movement of the throttle causes fuel to squirt from the nozzles between the primary throttle bores. If it doesn't you can bend the flat part of the arm to insure it does.

As for the secondaries, I'd suggest a heavier spring on the sec diaphram to delay when they open just a bit.