Sorry this will be so long but I hope you someone can help or get me pointed toward the right direction. My engine feels like it has plenty of power, but it will sometimes backfire through the carb. It is a 355 that has a comp magnum 305h cam, sportsman II heads, a holley street dom. tall intake, holley 3310 carb and mallory dual point dist. It has also been balanced. The engine was built by a very good engine builder. It has been broke in but not really ever been on the road. It has also been setting for awhile but ran often. Also the carb was a used carb. If anyone could tell me how to ajust it that would be great. Sorry if I left anything out, if I did let me know and I will try to let you know what it is. Btw I am really a newbe to this. Thanks very much

If it backfires when you 1st step on it is to lean on pump shot. If it has a 25 go to a 28. With this cam you need extra pump shot plus as much crank timing as it will take.(Be sure to disconnect vac. advance when setting time.)

What compression/gears/convertor/etc are you running? I have seen a lot of cars with big cams and intakes (and the 305 magnum is definately a big cam) that will pop back thru the carb if they have insufficent stall speed in the convertor or too high of gears...no torque and a lot of load dont go together very well. What is your initial/total timing, power valve size, jetting, etc. It could just need some tuning.

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'78 chevy truck-355, 9.4-1, vortec heads, XE268, vortec rpm intake, 750 edelbrock, flowtech headers and terminators.

'77 Nova-slowly progressing project.

'78 Nova-parts car?

'95 Lumina 3.4L DOHC 210hp daily driver

[This message has been edited by travis (edited 12-07-2001).]

Are you sure your spark timing is ok?

Guys it has a 3000 stall in it. I had it cranked up today and it seemed that the carb was flooding out. It was burning very rich. it was still doing the popping back. But this time it seemed as if it was getting way to much gas. Thanks for the help so far.

Sounds like you have blown the power valve...1 good backfire is all it takes. Might want to make sure your float level is set correctly too.