When I get in my car sometimes it starts right up and runs fine and other times it backfires through the carb and won't idle for crap. I am running a Holley 700 dp. It supposed to have power valve protection, so I am kind of thrown for a loop what else could be causing it. The only way I can get it to run right is to let it run at 2500 rpm for a minute or two then it does okay. I have been running the carb for a few months with no problems until a week or so ago. Any ideas? thanks

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87'IROC-Z 357
13.4 @ 103mph(on street tires)

 

Perhaps your floats are set too high or the needle valve is sticking?

 

I can shake the car and see the gas level in bowl. I have the clear sight plugs so I can keep a close eye on it.

 

Backfiring through the carb is usually a lean problem...not rich. My first guess would be some sort of choke problem. Maybe not engaging for whatever reason.

If truly flodding then I would also say a sticking needle. The next time it does that, shut the car off right away, and go check the float level then...make sure it's still below the sight plug.



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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

you know what? you may not be flooding i had this same problem, but it turned out my fuel pump was bad and it eventually would die on me if i drove it too much and had to wait like 30 minutes before starting it and continuing my drive home, check the fuel pump.

 

My choke is gone, I removed it when I put the carb on, so I need to check to see if the needle is sticking. Thanks for the information. I'll let you know if thats the problem. Thanks again.

 

Backfire is lean. You need a choke!

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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro

 

my car started doing the same thing today. i have a clear fuel filter so when when it died at idle i could see that the fuel was boiling. it would do ok if i wasnt idling very long but i was driving through some heavy traffic. tomorrow i gotta figure out how to keep it from boiling.

i think the backfires would be caused by a lean condition since all that may be reaching your bowls may only be vapors.

im not real sure on this, my problem had just started today.

its an idea though

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former 305 crossfire fuel injection
350 cubes
hooker headers
750 vac secondary
700r4 with shift kit