[1970fastcat]

So I got my new timing chain swapped in. She runs much smoother, and the first thing I noticed was I had lower the idle quite a bit. Not sure why, maybe the gear drive cause a lot more friction? I went to the parts store to pick up some exhaust manifold gaskets because the copper ones I have wont seal. One of the leaks melted a wire loom, so had to get it taken care of.

Anyway, on to my question. When I got back after getting her warmed up, I decided to check my vacuum reading. When I pulled the vacuum cap off the back of the carb, the idle increased to at least 1500 RPM from about 900, and stayed there. Shouldn't it peter out when the cap is pulled? The timing is still sitting at 18° at idle. I have the secondary butterflies open just slightly and the primary butterflies are only about 1 to 1 1/2 turns open with the idle screw. Does this mean I am running rich at idle?

 

[Art]

Does this mean I am running rich at idle?

It means you have a vacuum leak.

 

[1969XR7Vert]

It means you have a vacuum leak.

?? This makes no sense, at least to me. If he had a vacuum leak, the engine would pickup speed if he limited airflow at the carb airhorn. One check I always do, put your hand carefully over the airhorn and begin to progressively limited the air in, if the engine picks up speed significantly -> vacuum leak.

Adding more air as Mike describes should make the engine run worse/lose rpm in my view.

 

[ahunt191]

It sounds like an idle mixture problem to me. Here are the instructions from Holley on how to adjust your idle mixture screws.

QUESTION How do I adjust the mixture screws on my carburetor?
ANSWER To set idle mixture screws:
1.Get the engine up to temp
2.Shut the engine off
3.Install a vacuum gauge to a full manifold vacuum port
4.Turn the screws all the way in until lightly seated
5.Next, back them out 1 full turn and restart the engine making sure the choke is completely off
6.While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved. Be sure you keep all 2 or 4 screws even. You can also do this adjustment without a vacuum gauge, the adjustment are the same except you will adjust to highest engine RPM at idle.

Here is a video from Holley.

http://www.youtube.com/watch?v=UPGLUsW5ZeE

 

[CougarCJ]

Exhaust manifold gaskets?
My cars didn't come with them from the factory.

 

[cougarshaman]

Uh, header gaskets, I think, CJ.

I think you should try reading the plugs and see if it's running rich or what. If adding more O2 makes it run faster, then that means it was in oxygen debt (rich) in my experience.
Probably need to readjust the carb all over again, and stuff, yo.

 

[1970fastcat]

Tis definately not a vacuum leak (though I was somewhat worried about one), per Bob's method. It just sputtered and died, never tried to raise RPM. It did try to suck air through the float bowl though, the boosters where dribbling when I pulled my hand away.

I did mean exhaust minifold gaskets. I know they didn't have them from the factory, but Fel-Pro does make them, thankfully. Out of all the different header gaskets I have tried (including the latest waste of 30 bucks, copper) the steel/fiberglass exhaust manifold gaskets seal best. And they have yet again proven me right, I have no more leak on the passenger side (have yet to change the drivers side).

I played with the idle screws a little and now seems to run best with only 1 turn out. After adjusting them I pulled the plugs again. If I pull the one from the back of the carb it tries to peter out slowly, but never dies. If I pull the one off the spacer, it raises 100 RPM now. Odd maybe?

Either way, it runs MUCH better and smoother with the chain. No 3200 RPM timing bounce while cruising now. Plus now I can hear my solid lifter clatter.

 

[Sal]

the steel/fiberglass exhaust manifold gaskets seal best

I agree with that from experience, plan on ordering a set of felpro when I do my shorty headers.

Still learning from you guys about carbs

 

[Art]

Does this mean I am running rich at idle?

It means you have a vacuum leak.

Let me clarify. Idle speed goes up because you created a vacuum leak when you pulled the hose off.

And agree with the Fel-Pro header gaskets being superior. What I use.