For all you vacuum guage soothsayers

[drew8mc]

The more I think about this, the more I think I have some kind of vacuum leak. I can back off of the idle screw so it's not even touching the linkage, and it still idles at 800. The idle mixture screws have very little effect on anything, while being fully out of the transition slot. I've got to be sucking air in somewhere.

[geezer#99]

Sucking in air!
You say primary is closed enough, what about the secondaries?

[drew8mc]

Secondaries are closed now too. Once I figured out the slot was not overexposed I closed them back up.

[geezer#99]

How about the high idle screw?

[drew8mc]

Could be engaged. But it does kick down from about 1500 with the choke on. I will check it when I get home.

[drew8mc]

OK... I am partway there.

I had a long list of troubleshooting items to go through. I only got to item 2 before it looks like the popping sound is gone. I didn't hear any noise out of the valve train either.

Plug Wires!

I swapped my old set in and no more of that misfiring sound. No power drops or hesitations. These were brand new wires from DUI. I will probably pick up a different set in the future. These are old Summit wires from who knows when.

However, this thing after warm up is still idling at 1400. On startup it idles at 850. I'm thinking I might still have a vacuum leak that only shows up after it's warm. Is that possible? I checked the fast idle cam and screw and it is not engaged.

[geezer#99]

What gasket between carb and intake?
I’ve had gaskets hang up on the butterflies.

[drew8mc]

I just checked the butterflies. They don't seem to be getting hung up on anything. I think the gasket was an open style... not the four hole style.

[Richard2112]

Gasket leaks after warm-up is commonly intake manifold gasket. But it depends on manifold type, heads, etc.

[drew8mc]

That's what I feared... but at least I know I don't have valve train issues anymore.

The intake was one of the only pieces to come from the old motor. The end of life of that motor involved losing the harmonic balancer and all pulleys. Limped it home with steam hissing out the front. I bet the intake got warped.

[kwmech]

Did you get anywhere with this? Did you run the valves and adjust them while the engine was running?

[drew8mc]

This still goes on.

I put a new intake manifold on and made sure to seal it well. Now the idle holds steady, but I'm back to square one with the misfire.

I started a new thread for the latest problems.

http://67-72chevytrucks.com/vboard/s...64#post8570364

I don't hear anything out of the valvetrain anymore. Maybe I was hearing an exhaust leak.

[kwmech]

So the answer is no to a valve adj? tight valve can give you an issue as described

[mattfranklin]

Oops. Wrong thread. See his later one. Admin: please delete this reply.