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.

Sounds like the rear half of the carb has either a low float level, or the rear accelerator pump is not working properly.
David

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67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350
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Too lean and/or too retarded

timing too advanced will do that too..

I think davidpozzi has the right idea. the secondary acc. pump isn't working or is timed wrong.

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!

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.

1<Put a timing light on it. 2>Verify proper vacuume advance, 3>Tune carb w/ vacuume guage. Then start pulling things apart.

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

Also if your timing chain is off a tooth will produce that problem as well. Tackle the easy things first.

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68 RS red w/ white stripes
67 SS/RS restoring

Almost forgot, too tight of an adjustment with the valves will produce it as well especially and intake valve.

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68 SS 396

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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375hp 78 Chevy truck
77 Chevy Nova
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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.

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

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

Scooby, sorry I didn't see your message before I wrote my previous reply, but you have a good point so if i have any more trouble I will try leaning it out instead of making it richer.

-Nick

Well guys I finally fixed the problem, and it ended up being TIMING and maybe a little something to do with fuel. But I never knew that you had to set timing with the vacuum advance line plugged up! I had a buddy come over and he showed me that trick, then we set timing right, and she ran like a screaming freaking demon! But thanks for all your help.

-Nick

Nailed It!

Glad to hear!! I think timing is probably the most common culprit. Even with my carb running extremely rich, the backfiring got a lot better once I got my timing correct!

Dave

<BLOCKQUOTE>quote:</font><HR>Originally posted by Scooby Doo:
Glad to hear!! the backfiring got a lot better Dave<HR></BLOCKQUOTE>

How is your new backfire better than the old backfire?