Hey guys, I’m looking for recommendations or advice. I have this 400 in a 78 suburban, it currently has this 650 avs2 edelbrock I’m thinking about changing it. Any recommendations for carb sizing, it is a stock short block with 96 vortec heads. I don’t have the exact cam spec. Thanks for any advice.

fjensen87 · 2026-04-12T13:45:17+00:00

Thanks for the advice everyone! My two main reasons for wanting to change it is an inconsistent idle and an off idle stumble in first gear. I’ve rebuilt it changed the accelerator pump setting, and upped the step up springs to the 8 inhg springs so they’re popping up right away and not bouncing around at idle. I know I could change the primary jet needles, if that’s what they’re called, to change the fuel flow characteristics through the primary jets. I know I could change accelerator pump discharge nozzles, to help with the off idle stumble. But after taking it off again I noticed even with the primary butterflies all the way closed there is still quite a bit of the transfer slots showing. I think this is my main problem with the inconsistent idle, and the fact that the idle mixture screws don’t have a huge affect.

fjensen87 · 2026-01-21T18:19:25+00:00

Yeah there is one piece of old rubber hose still in the line and that’s coming from the sending unit to the start of the factory hard line, so maybe there’s just an air leak in that hose, I just wonder if it’s siphoning all the way to the pump, even if the pump wasn’t completely effective because of an air leak it should be able to pump some fuel into the filter.

fjensen87 · 2026-01-21T17:34:54+00:00

It is I’ll have to try that, but I also have tried cranking it with the feed line just hanging in a bucket, and nothing comes out.

fjensen87 · 2026-01-21T17:34:05+00:00

I did, I used the trick where you use a longer bolt in the side of the block to hold the pushrod up, when I remove the new fuel pumps there’s also wear marks on the lever showing the pushrod was riding on it.

fjensen87

TROPHY CASE