Inliners International Forums General Discussion Engines 250ci stumble and backfire????????

Hello I-sixers
My chevy 250 with a rebuilt head, offy intake, DEMON 525cfm 4brl, and headers. Stumbles or backfires through carb under hard acceleration, and accelerates roughly. I have a stock cam and head (for now). I have tried a lot of things, like adjusting timing, accelerator pump and float leves, but it does not change much. Any info would be very helpful. thanks!

Have you checked for any vacum leaks ? also have you check the vacum advance on the dist. Ihave ran a 600 holley on a Offy Stock motor other then headers so I don't think it is a carb CFM issue But also How do your plugs look. Fouled plugs can also give you these types of problems.
hopr this helps }[oooooo]

Have you replaced your plug wires lately?

I have had this problem with more than one modern engine and replacing the wires fixed the problem. Higher energy ignition systems tend to break down the wires fast. Incidentally, they really aren't wires at all, as you will see if you cut one open.

Twisted6,
I have checked for vacum leaks and do not appear to have any and the vacum advance seems to be a little stiff. this could be the culprit.

Thanks for the help. the real culprit was fuel starvation. The squirters in the carb were smaller than the manual. so I installed bigger one and solved the problem.