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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I have a zz4 with a holley 670 avenger,just changed from

Customer Question

i have a zz4 with a holley 670 avenger,just changed from factory aluminum intake to a edelbrock rpm air gap,,now the carb is spitting back when i accelerate,have checked everything,it seems to be leaning out has completely died twice when im trying to pullout on the hiway,bout got me ran over,its in a 52 chevvy pickup,will haul tje mail but u cant get on it hard, same truck,same carb,never happened with old intake,,i need some help,,
JA: How old is the transmission? Have you checked the fuel filters?
Customer: trans is newely rebuilt, fuel filter has about 10,000 miles more than the engine it has 7000 on it same as tranny,
JA: Are you fixing your Avenger yourself? What have you tried so far?
Customer: havent touched itother than to visually check the accelerator pump,its pumping a good stream but im wondering if this manifold may require more pump then i the card came with,,
JA: Anything else you want the mechanic to know before I connect you?
Customer: the inability to accelerate without the popback is my problem..
Submitted: 1 month ago.
Category: Chevy
Expert:  Jared D replied 1 month ago.

What you are describing sounds more like a timing issue than a carb issue. When you swapped out the intake are you sure you got it re-timed correctly?

Customer: replied 28 days ago.
Yeah the timing is as far advanced as the starter will permit,,about 14 degrees b t d,tried it all the way from 8 to 14,,best running where it is now,,still popping,,
Expert:  Jared D replied 28 days ago.

Plugs look ok? No wires crossed? No lightning trails in the distributor?

Customer: replied 27 days ago.
new plugs,checked wires three times,distributor looks good,i have a phenolic spacer bewteen carb and intake that im removing plus im adding a 50 cc accelerator pump ( has a 30 now) and if that dont do it im never gonna call my self a mechanic again,i have noticed the more timing i give it the less it pops but i cant go any higher because it wont start,the starter backs up,,if you know what i meam,excessive timing will cause the starter to drag and draw massive current,,,it has aluminum heads and a roller cam,its a really nice engine about 380 h.p.,its a shame i cant accelerate,,it usually smokes the tires,,not now though,,its turning my carb black from soot on the inside,,,the pop sounds like it right in the top of the carb,,think about it,,call all you hot rodder buddies,,
Expert:  Jared D replied 27 days ago.

I would probably bump up the accelerator pump as you mentioned (a lean condition can cause a pop like you describe) and then look for vacuum leaks. I like to use break cleaner and spray all around the intake and carb. If the engine revs then there is a vacuum leak. Be prepared with a fire extinguisher nearby in case there is a major vacuum leak. If it ends up firing out of the intake because of a particularly bad vacuum leak it could ignite the brake cleaner.

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