Engine RPM sticking at 2000 rpm

Here's an interesting problem I've been trying to troubleshoot.

After sitting for 3 years, I finally have my AMX running again with the T5 trans conversion, new headers, and rebuilt 750 Holley in place of the 600 that was on there. The 750 received a replacement primary throttle shaft, billet primary metering block, electric choke conversion, and quick change secondary kit. It's got a large diameter drop base air cleaner. The gas pedal is a later model with a cable instead of the original bigfoot pedal.

It's got a Duraspark distributor and an MSD 6AL, and uses ported and manifold vacuum via a TVS valve on the water neck. The vacuum advance can is the stock one for the distributor, from a late 80's Wag.

Other than the carb, no changes to the engine.

When I drive it though once I increase rpm above 2000 it won't come back down under 2000 unless I give the gas pedal a quick stab, then it settles down, although it seems to settle a little slower than I'd expect. But as I slow to a stoplight and then push in the clutch it revs to around 2000-2200 rpm once the load is off the engine.

Should I tell you guys what I've already tried, or do you want to take guesses and I can tell you then? I'm trying to make this fun you know...

Edited by Greyhounds_AMX - Jul/21/2018 at 10:47am

Misaligned throttle plate (s).
Miss adjusted secondary idle stop

to name the obvious that comes to mind.

Edited by Boris Badanov - Jul/21/2018 at 11:04am

1) Frayed or rusted cable.

The cable looks great with no rust. I lubed it - no change. Swapped in a different one - no change.

2) Delaminated plastic on same.

There's no plastic on the exposed cable that I can see, and the black plastic dust shield has been trimmed off so it can't interfere with anything. I'm pretty sure the cable isn't the issue.

3) Bad or missing return spring.

Checked that - all good. Plenty of spring, although I suppose I could add more for testing just to make sure.

4) Frozen or sticking choke parts.

I pulled the carb again and removed the electric choke assembly, all looked good, moved smooth. Reinstalled, no change. Pulled the carb again and swapped to the choke assembly from my old 600 - again no change.

5) Misaligned throttle plate (s).

Checked and readjusted them, no change there.

6) Miss adjusted secondary idle stop

I use a SST set screw for a stop so it's easy to adjust from the top if needed, and have that adjusted to show about 0.020" of transfer slot since I've had the carb off so much. The drivers side secondary linkage is adjusted spot on and ensuring the secondary is closed when the primary is closed.

You guys have almost caught up to me already.

I'm convinced the choke is ok, after messing with it quite a bit then finally swapping it completely. I even changed the choke lever on the throttle shaft.

There is a Ford style kickdown lever flopping about though. I'm pretty sure that's not it as I had it locked in place with a set screw to start with, then took that out too see if it made any difference and it didn't. I'll cut that off though to be sure!

I would be tempted to run without the CTO vacuum switch and see how the advance reacts on the dist.