Flat spot off idle..

[gearjammer]

1971 225 1 BBL Carter...Drivability problem:

Runs good when the choke is still engaged. One the choke opens up most all the way, say 6-7 min of driving, Truck has a flat-spot, hesitation, just off idle . Like when pulling away from a stop light. If I didn't know better feels like the accl. pump was bad. It's new, choke pull off is new, choke stove is new, fresh carb rebuild.

Feels lean...anybody ever drill the jet out? Any ideas?

[dodgeboykim]

Vacuum advance working correctly, Maybe Jets like you say, Timing off a bit or possibly a loose timing chain. Accelerator pump not set up correctly.

[Dood]

Vacuum advance working correctly, Maybe Jets like you say, Timing off a bit or possibly a loose timing chain. Accelerator pump not set up correctly.

The vacuum advance is an easy thing to check. If you have put in a new/reman distributor, they can sometimes have the vacuum advance setup all wrong. A stretched timing chain is another real possibility.

But now that I think about it... you said there is no problem before the choke opens? I see why you are thinking fuel. Does it have any of the other lean behaviors? What do the plugs say?

[gearjammer]

I think it really could be timing....but I HAVE checked trhat and it seemed in the ball park, Maybe it needs another look...But it just feels lean...

[DodgeDirty1963]

Is it the Carter carb? It could very well be leaning out, make sure you have both check balls and the one for the accelerator pump is seating properly. Could very likely be the accelerator pump too. I went through 3 of those Carters trying to get rid of the flat spot with my slant six. Not that they're bad carbs or anything I've just found them to be problematic because I never know what was done to them (air bleeds filled in, etc.) I don't think I'm necessarily a hack either, I've rebuilt alot of Autolites, Holleys, and even a Quadrajet that worked good. But not good luck with the carter, I thought "are you kidding me?! It's ONE barrel!! I ended up using a Holley 1945 I slapped on straight out of the junkyard that works perfectly.

[oklamopar]

The slant that was in mine had the holley 1920. And after replacing the worn timing chain and bumping up the timing a bit, the flat spot went away. Before that I had to turn the idle up and make the pump throw a bit more than the 3/16 recommended setting. Mine was a manual transmission so the idle at 850 was easy enough.
also check the springs and weights in the distributor that they are moving free. Like dodgeboykim wrote check the v/advance. Mine was adjustable. I can't remember how I set mine.
most flat spots that have plagued me were accelerator pump and timing related.

[dodgeboykim]

Mine was adjustable. I can't remember how I set mine.

Probably a small allen wrench put into the tube where the vac hose slips onto the vac advance pot.

[StinkFinger]

I was running an eddelebrock performer (carter) and had the same problem I messed with it a lot and it got better but never went away. I am now running a holly street avenger vacume secondary carb and my flat spot is gone I have way more power and if I stay out of the secondary's noticeably better milage