sbc 307 backfire on hard acceleration HELP!!!! - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-23-2012, 02:17 PM
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sbc 307 backfire on hard acceleration HELP!!!!

Ok guys this is my first post!!!! Glad to join the forum.
I have a sbc 307 w/ edelbrock performer intake topped off with a holley 670 street avenger carb. I recently installed a summit k1101 cam with 194/204 degrees at 50 thousand. Has 187 58cc heads from a camaro with 1.84/1.50 int. Exh.. I put it together and everything worked and runs smooth my problem. Is that on hard acceleration it will back fire and then go. When in park or nuetral this isn't existent. Only when driving and as soon as I wanna punch it a lot it back fires. Just today I reset my idle screw and advanced the timing a little bit and it seemed to.get better ill have to advance it some more later today. I am using ac delco #2 with a .035 gap with super stock wires and mallory proform coil... It's backed by a tci th350 with 373 rear end along with headers in my s10 blazer... Any help is appreciated it ran fine before but.it had 72cc could I.be getting to much fuel:'(

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Old 04-23-2012, 05:16 PM
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Quote:
Originally Posted by godfatheritalio
Ok guys this is my first post!!!! Glad to join the forum.
I have a sbc 307 w/ edelbrock performer intake topped off with a holley 670 street avenger carb. I recently installed a summit k1101 cam with 194/204 degrees at 50 thousand. Has 187 58cc heads from a camaro with 1.84/1.50 int. Exh.. I put it together and everything worked and runs smooth my problem. Is that on hard acceleration it will back fire and then go. When in park or nuetral this isn't existent. Only when driving and as soon as I wanna punch it a lot it back fires. Just today I reset my idle screw and advanced the timing a little bit and it seemed to.get better ill have to advance it some more later today. I am using ac delco #2 with a .035 gap with super stock wires and mallory proform coil... It's backed by a tci th350 with 373 rear end along with headers in my s10 blazer... Any help is appreciated it ran fine before but.it had 72cc could I.be getting to much fuel:'(
Most likely you have an adjustment issue with the carburetor accelerator pump. Whn you stab it hard the pump shot needs to start right away and be sufficient to satisfy the fuel need. You are most likely experiencing lean backfire due to a lack of fuel. It wont happen in park as there is not enough load on the engine.
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Old 04-23-2012, 08:45 PM
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A combination of not enough accelerator pump shot or a delay in the shot response. and not enough initial spark advance.

You probabily will need to recurve the dstributor to get it right.
More initial base timng gives sharper throttle response but the max at max advance cannot exceed what the motor needs to create best power.

Try 14 to 16deg at idle and 32 to 36deg at max advance.
Then create a mechanical curve that allows this.

Carb pump shot is a matter of linkage arm adjustment, pump cam choice and location and the size of the discharge shooter orrifice.

Any lag in the shooter response with throttle movement needs to be adjusted out.

A air fuel ratio gauge is a big help to get the carb dialed in.
jetting.poer valve, shooter, idle circuit.

Eliminate all possible manifold,carb vacuum leaks.

The plugs,wires, cap, rotor and coil all need to be in A-1 condition.
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Old 04-24-2012, 08:44 AM
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Everything is new I readjusted the rocker arms and it seemed to go away when its warm of course. And the timng is set to 4 btdc with my idle close to 600-800 in drive seems to be working fine appreciate your fast response!!! Thanks guys
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Old 04-24-2012, 08:10 PM
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Read this link on ignition timing. It has some good recommendations at the end of the article.

I think you will get much better performance with more timing.

http://www.corvette-restoration.com/.../Timing101.pdf
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