backfiring out the carb - Team Camaro Tech
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post #1 of 20 (permalink) Old May 17th, 01, 01:56 PM Thread Starter
 
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I have a 383 Stroker, with HEI distributer, and a Holley 650 double pumper. It idles fine and will rev up slowly just fine, but when i punch the gas it will backfire out of the carb. It almost seems that when the secondarys open it does this. But I can't understand why if i rev up slowly it will work but fast it backfires. Please help.
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post #2 of 20 (permalink) Old May 17th, 01, 02:31 PM
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Sounds like the rear half of the carb has either a low float level, or the rear accelerator pump is not working properly.
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post #3 of 20 (permalink) Old May 17th, 01, 03:36 PM
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Too lean and/or too retarded
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post #4 of 20 (permalink) Old May 17th, 01, 05:31 PM
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timing too advanced will do that too..
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post #5 of 20 (permalink) Old May 17th, 01, 06:08 PM
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I think davidpozzi has the right idea. the secondary acc. pump isn't working or is timed wrong.

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post #6 of 20 (permalink) Old May 17th, 01, 08:04 PM
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gards79,

i think david hit the nail on the head! i would take the carb off the motor and pull the rear fuel bowl. clean the metering block and the passage's in the carb body with compresed air and carb cleaner. do the same for the bowl and pump. re-assemble and adjust the pump lever. fill the bowl with fuel via the vent and check the pump operation. re install the carb.

check it on the car running, if it still give's you a lean backfire try a larger squrter. good luck!
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post #7 of 20 (permalink) Old May 18th, 01, 02:16 PM Thread Starter
 
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Well thanks for the help guys, I will try these things out on Sunday, and will keep you posted. Also, I have heard from several people that the distributor could be "off a tooth," and that is what is making it backfire. Does anyone agree with that theory? I am just reluctant to pull it out and try to realine it cause I think I would end up making it worse than it is. So that is a last resort.
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post #8 of 20 (permalink) Old May 18th, 01, 05:55 PM
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1<Put a timing light on it. 2>Verify proper vacuume advance, 3>Tune carb w/ vacuume guage. Then start pulling things apart.
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post #9 of 20 (permalink) Old May 18th, 01, 09:23 PM
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No, the dist off a tooth doesn't really make a problem, except you might not be able to rotate the dist body far enough without the vacuum canister hitting the block or something. If the timing is OK by the light, it is OK, no matter how many teeth you are off. You want to check the static, centrifical and vacuum advance. There have been lots of posts on setting timing, a search should find some.
-ibjoe
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post #10 of 20 (permalink) Old May 18th, 01, 09:52 PM
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Also if your timing chain is off a tooth will produce that problem as well. Tackle the easy things first.

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post #11 of 20 (permalink) Old May 18th, 01, 09:56 PM
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Almost forgot, too tight of an adjustment with the valves will produce it as well especially and intake valve.

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post #12 of 20 (permalink) Old May 19th, 01, 02:35 AM
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Could be valves adjusted too tight, exhaust lobe going flat, a major exhaust restriction, heavily retarded timing, or even 2 crossed plug wires.

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post #13 of 20 (permalink) Old May 20th, 01, 09:16 PM Thread Starter
 
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Thanks again guys for your help, I'll let you know what happens when I finally get a chance to work on it, first things first, I'm gonna try a bigger pump squirter.
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post #14 of 20 (permalink) Old May 23rd, 01, 01:50 PM
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gards79,

I feel for ya. Search for the thread titled "Can't stomp my 396". I had the same problem but turns out the carb was running too RICH, not lean. The engine will bog if it runs too lean.

Take a look at your exhaust, do you see any droplets coming out? (you'll have to distinguish between gas & condensation, gas will stain the concrete) Does it smell like gas? My secondary needle was shot and the secondary float was set too high.

Let us know...

Dave
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post #15 of 20 (permalink) Old May 23rd, 01, 02:55 PM Thread Starter
 
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Well guys, today I put a bigger pump nozzle on the secondarys and it helped out a lot. But I don't think that the problem is totally fixed. Now it only happened once, but when the engine was cold, I started it and waited a couple of seconds and floored it and it backfired a little. But after it warmed up, it never did it. I went and drove through town the other day as well, with out the new nozzle on, and it never backfired at all, but I did keep my foot off the gas too. I don't know, I will have to do some more testing to see when and if it does it anymore. Thanks for all of your help though.
-Nick
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