350/350 exhaust back fire
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
350/350 exhaust back fire
Is it normal to hear the back-fireing when slowing down from a hard run? The vette has moderatly loud mufflers. Just got the car last month, did the Lars timing (fantastic performance). I'm thinking about adjusting the hydraulic lifters. Any ideas?
Racer
Joined: Jul 2003
Posts: 455
Likes: 0
From: Buffalo New York
as I understand it, backfiring on deceleration is a lean condition. Someone who knows more than me will hopefully chime in and I would guess suggest checking the carb and perhaps going up a couple of sizes in jets...
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
That is how I remembered it too. There was a debate between a couple of knowledgable members and the recognized expert suggested lean caused the poping and rich didn't have enough oxygen to sustain combustion in the pipes.
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
Usually indicative of a lean condition. Back your idle mixture screws out a little and see if it helps. If it does, you can try richening it up a couple of jet sizes. Have you re-jetted the carb for the free-flowing exhaust, or are you running stock jetting? If so, you are certainly lean.
Lars
Lars
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
Usually indicative of a lean condition. Back your idle mixture screws out a little and see if it helps. If it does, you can try richening it up a couple of jet sizes. Have you re-jetted the carb for the free-flowing exhaust, or are you running stock jetting? If so, you are certainly lean.
Lars
Lars
PS Your paper on initial setting timeing was great!
Thanks.
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Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
That carb comes stock with 66 jets on the primary side. Swap in a set of 68s and set idle mixture screws to 1 turn out as an initial setting.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 207
Likes: 2
From: Key Largo Florida
I'll re-jet (the heck w/Holley reps), but where should the vacuum advance connection go? I thought below the throttle plate was right.
Racer
Joined: Jul 2003
Posts: 455
Likes: 0
From: Buffalo New York
so you switched from manifold to ported vaccum. Go back and take a look at Lars' papers.
As I understand it, Manifold vaccum will increase performance. Switching to ported vaccum changed your timing curve causing you to lose performance.
Follow Lars' advice from above. Go back to manifold vaccum and jet the carb up to 68.
As I understand it, Manifold vaccum will increase performance. Switching to ported vaccum changed your timing curve causing you to lose performance.
Follow Lars' advice from above. Go back to manifold vaccum and jet the carb up to 68.
