I have a '68 396 that is pretty much stock except for the Weiand high rise (single plane) intake and the Holley 750 carb. It starts right up and once warm - idles like it should. If you jam on the gas pedal - it cuts right off or sometimes backfires. Then going down the road it will go through 1st and second gear great, but when it hits third, it's like it is running on 6 cylinders. Popping and sputtering. I've been all through the carburetor twice and changed the jetting and the mixture and every other possible adjustment. Nothing seems to make the least bit of difference. Now I'm thinking it could be a points/distributor problem - but it only started this after I installed the carb and manifold. Coincidence????

How much pressure is the fuel pump delivering? If the fuel pump is not providing adequte fuel flow, that could be one possible cause for the high RPM problem. The other problem, cutting out and backfiring when you floor the accelerator pedal, sounds like a misadjusted acccelerator pump, or the timing may not have enough initial advance. Have you tried moving the accelerator pump cam? And, have you adjusted the gap between the accelerator pump arm and the actuator on the throttle linkage? Last, make sure the timing is set correctly.

I was kind of thinking the same thing - fuel pump or timing. I bought the car a month agao - so I still have a lot to figure out from what the last guy did to it. Thanks for the tips...I'll look at it this weekend.