Looping idle

[pablo_max]

Hey guys.
I have a bit of a looping idle issue.
I assumed that it was a vacuum issue, but as it's a 72 with basically no lines I am not sure where it would come from.
I have checked the manifold, the carb mounting and the advance. All seem fine.
It loops under 900 RPMs by 50-100 RPMs.

The only other thing I have noticed is that it feels a little as though it's starving out at high RPMs when I give it the beans. If I back off on the gas though it does OK up in the high RPM range.
I dont recall that it did this before I have the electrical system replaced.

I checked the timing today and I set it at 10 BTDC with the vacuum advance off and plugged.
Any ideas on where to start?

[shackwrrr]

have you checked the EGR. It can cause a rough idle if it hangs open. Also If it is stuck slightly open and wont open anymore you can get a stumble because the mixture leans out without the exhaust gas in there

[pablo_max]

true...
I dont have an EGR though.

[shackwrrr]

I guess that would make the diagnosis different.

Look for a lean condition. Either a fuel pressure issue a leak or maybe your float height is changed for some reason.

[pablo_max]

I wonder about the pump. I dont have a filter before the pump only after.
I did drain the tank and clean it out though when I soldered the vent tube back on.
I will check the bowls again tomorrow I guess.

[shackwrrr]

have a propane torch. Crack it above the carb and see if the idle smoothes out

[pablo_max]

I have one..but what would that tell me?

[Serious Johnson]

I have one..but what would that tell me?

Smoother (not just faster) idle would tell you that your idle mixture is too lean, which you ought to be able to fix with the mixture screws. You can also wave the torch around (unlit, of course) to pinpoint vacuum leaks.

S.J.

[Ristow]

Look for a lean condition. Either a fuel pressure issue a leak or maybe your float height is changed for some reason.

yup.

[pablo_max]

Yup...seems it was a bit rich. I gave the idle screws about 1/2 turn and it smoothed out.
Although, I still get the popping when going down hill under an engine break condition.

[shackwrrr]

popping under decel is usually a timing thing. I am thinking retarded but Im not sure.

[pablo_max]

Its set at 10 BTDC currently.
The books says 5 though. I dont have a sticker on the hood, so I dont know what it was set for the factory.