'71 fj40 carb issues

[torfab]

I have a '71 with an F engine. Timed it to 12*, and have been finely adjusting the idle mixture to idle with 20 pounds vacuum at 650 rpm.

once in a while (usually when it's still cold - but not every time) it will start running extremely rich.

the result is the idle will drop to 400 rpm, vacuum will be reduced to 15 pounds, and it will run rough.

If I run up the rpm for about 30 seconds, it will correct itself and start running properly again.

My thought is that the float is sticking, or the carb might be clogged up, but not sure where to start.

Any ideas?

 

[65swb45]

Thots. A sticking float would flood the motor out, not just make it run a little rich.

At idle, you should be running just off the idle circuit, which on it's own doesn't run rich; it is a very small circuit.

Now if you had an issue with a distributor that was slightly more wobbly when cold, that could throw your point gap off, weaken the spark, weaken the vacuum, and drop the idle.

A guy named Eric Gunter came in to my shop with this scenario about 12 years ago or so. Had to keep the truck overnight to confirm it. You can check this theory out yourself by just checking dwell at start up against dwell warm.

Best

Mark A.