Hi, I have a 72 Chevelle SS with a 402 in it. It does have an aftermarket cam in it, do not know the specs on cam. Has a Holley 4150 dual pumper carb. Sometimes, especially when it sits for a long period, it will backfire when starting it. I have replaced the power valve, but did backfire after I replaced it, so will probably have to do it again. Any suggestions on what may cause the backfire. It also smells like it is running very rich. Any ideas.

Adjust the mixture screws, get new plugs plugs, and check for good spark and correct timing. What kind of distributor do you have? Do you have any smoke out of the exhaust? If so, what color? Does it only backfire the first minute or so? Does it backfire out the carb or the exhaust?

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Trever Maas
1972 Chevelle Malibu
Mohave Gold
L65 350/M38 TH350
2.73 AXL RATIO
Undergoing Resotoration

[This message has been edited by malibu man (edited 05-29-2002).]

Thank you. It only backfires at initial start-up. And only if sitting for a long time. It backfires through the carb. I believe when it does smoke , is when initial start, and if I hammer it, and the color is white. I am running an MSD #8461 distributor, and a MSD Multiple Discharge # 6480 with MSD soft touch rev control #8738. I did pull a plug and it is black, dry. Guess will check carb adjustment. thank you for any additional advice youi may have. <BLOCKQUOTE>quote:</font><HR>Originally posted by malibu man:
Adjust the mixture screws, get new plugs plugs, and check for good spark and correct timing. What kind of distributor do you have? Do you have any smoke out of the exhaust? If so, what color? Does it only backfire the first minute or so? Does it backfire out the carb or the exhaust?

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[This message has been edited by chevelle402 (edited 05-30-2002).]

[This message has been edited by chevelle402 (edited 05-30-2002).]

sounds to me like it backfires because your accelerator pump well is dry after the car sits for a long time. I guess I would crank the car over with spark plugs out and fill the carb with gas such that you are getting a pump squirt and then re plug it and fire it up.

It also occurs to me that if you do not have the carb equipped with a choke you will experience the backfire problem until the engine warms up.

[This message has been edited by charbilly2001 (edited 05-30-2002).]