Need help tuning Autolite 4100

When I screw in the air / fuel mixture screws, the idle goes up and when I back them out, the idle goes down. I thought it would stumble because when the screws are all the way in, it cuts off the fuel supply.

Why is mine doing the exact opposite? Vacuum leak maybe?

 

Bttt

 

If the throttle butterflys are too far open it will be drawing fuel from the mains. If the power valve has a diaphragm leak it could be drawing too much fuel. At any rate it's getting fuel from somewhere else besides the idle circuits. When you close them it cuts off just the fuel in the idle circuits. Besides the power valve there may be another internal leak in you carb.

 

Sounds like your getting to much fuel if cutting off the idle circuit makes it run better, I'm no carb expert but the first thing that come to mind would be a stuck/sticky float. Whats the factory procedure for setting the Idle on that carb? Do a search for "Autolite 4100 still runs with idle screws all the way in" First result has some info. If I remembering my carb theory correctly it's not a vacuum leak, as it gets better when you remove fuel from it, I would think that removing fuel when there is to much air(a vacuum leak) would only make the car run worse.

I really like your galaxy BTW, really want one my self, in red or black would be killer

 

Some carbs in the emission era had "idle mixture" screws that regulated air instead of fuel. What year carb??

Cosmo

P.S. It's very well worth checking that the other settings are spot-on (float esp.)

 

4100 carbs have built in vacuum leaks. If the hot idle compensator (spring on air horn) leaks is bent or carbon coated it will create a vacuum leak. If the top cover is warped it will casue a vacuum leak. if the power valve cover is warped it will cause a vacuum leak and the power valve will not work properly ^ stated above if the power valve is blown out or the wrong one it will either cause a bog or stumble or hesitation or fuel leak (which it sounds like your problem) But when they are working right they are great carbs, I run 2 (two) on a 272 y-block....

 

Thanks everyone. The carb is a 1964 original to the car. I want to keep the car as original as possible that's why I'm working this carb so hard.

Do you think the power valve would have anything to do with it? I rebuilt the carb about a year ago but since then have had a couple of backfires from the carb and from what I understand, that reeks havoc on the power valve on this carb.

 

Ok Rick, I'll check the power valve and make sure its not the corporate. Nothing else is bent or warped and the car runs as smooth as hell but thought it was weird that when I tighten the adjustment screws all the way in, I was getting different results than everyone else. This carb has always ran fat as hell and have never figured it out. Hopefully I'm getting to the bottom of it.