Carburetor just rebuilt vacuum advance not workin will it cause a manifold to turn red.I will adjust timing after new one is on

No it would not, probably the divert-er valve (heat riser valve) on the driver side exhaust just under the exhaust manifold is stuck shut.

You should set the timing at 4 deg. advanced anyway.

It doesn't have a heat rider valve

Then it has to be in the timing, check to make sure it is not way advanced. The vacuum advance is not doing this, I have only seen this if timing is way advanced or the heat riser valve.

Also has that engine ben converted over to be able to run unleaded gas? That runs hotter.

Ok thanks I'll try the timing

It was fuel injection converted to carburetor does that have anything to do with it.I always use chevron 93

What year fuel injection? Later than the 70's?

Came out a 99 Tahoe

From 74 on up is when they started using the unleaded gas. Motors prior to this year would have to have different valves and pistons put in to handle the unleaded gas. The only other thing I can think of is if you have too hot of spark plug, or a plugged exhaust. There is no cat on there I hope.

99 is fine, no cat tho hey?

Could be running too lean as well.

Yes, definitely, right on there Roy. Check the settings on the idle mixture screws.

Been running fine for 2 years jus started whn i changed a cracked manifold

No cat & exhaust has been checked recently put on two years ago

So what size vortec is it? And this all just started after replacing the exhaust manifold? Running for 2 yrs. it's not lean, carbureted is no issue, thats ben done thousands of times, You must have just replaced the intake for the carb, so vortec heads, And why would the timing be off all of the sudden, right? What are we missing...What if anything computer wise is running that engine? Just all old style hook up? Any chance anything is plugging the exhaust on that side? Is there an EGR valve on it? I'm stumped at the moment.

Not tht I knw of

Ok then how about this, engine from a 99' Chevy, assuming you did not change the heads, the vortec heads are a high flow in design. You said you changed out the exhaust manifold. What is that exhaust manifold off of? I'm thinking if you put an exhaust manifold on from later years, the exhaust ports would be smaller than the ports in the vortec head, openings not matching thus causing restriction.