once highest vacuum is reach; do the other side. set idle rpm in gear. recheck. timing must be on the mark also

 

I will try it again in gear, and recheck. When you are turning the idle screws out should there be a point where there is too much fuel and the vacuum reading goes down. If so mine doesn't do that. I think the jets are too small. Any suggestions.

Thanks
Greg

 

The jets don't affect idle. When you're done both screws should be out about the same number of turns. The engine should run rough if the screws are turned all the way in, out doesn't usually have an affect. Set the screws for the best lean idle.

 

Agree with above and make sure ignition timing is set FIRST.

Tranny in gear, E brake on!/wheels blocked. Turn one screw in til engine falters and runs rough than slowly back out in 1/4 turn increments to reach highest vacuum.

Then do the same on the other screw. THEN...back to the other screw and back it out in 1/8 increments..if no change then put back 1/8 to where it was and go another 1/8 in to see if that makes a difference.

You'll find the 'sweet spot'. Just go back and forth until you have reached the highest vacuum reading. Back up into park and you may have to reset the curb idle screw.

That's it..good instructions above......John

 

I tried to set my carb [Holley 570 street avenger] with a vacuum gauge and not sure if it was done correct.

With the car running the gauge read 16-17. I turned the screw in on the passenger side dropping the reading to 15 ,then turned the screw out getting the reading up to 18. The screw was then turned out more and more with no effect on the reading.

If you turned the mixture screw all the way into the stop and it kept running, there is a problem (unless it is an emissions carb).

As for turning it out until it reached 18 hg and this was the highest reading, this setting and approx. 1/4 additional turn out is the optimum setting. Going out further actually richens the idle mixture. Both adjusting screws at the same adjustment means correct balance.

Doing this in gear will not change anything. The curb idle must be @ spec to adjust properly. If turning out and the RPM's increase, you lower the curb idle (tach on multi-meter) and continue to watch the gauge. This is done to not open the plates too far exposing the transfer slot.

If when put into gear and the curb idle lowers too much (loading up), you may have a vacuum leak or maybe a bad torque convertor (or bad/incorrect power valve or a host of other problems).

Have you crossed your present jet size with the HOLLEY List Chart?

 

engine with no load doesnt need much fuel, I see it best in gear, less time getting it right

 

Thanks that clears a lot of issues up. I was expecting the vacuum to drop when the idle screws are turned too far out. I will set the car up and try this out.

Greg

 

Setting idle mixture using a vacuum gauge is not very precise, as you noted in your last post. As you turn the screws further out, the mixture is getting richer, but still being burned, so the RPM doesn't change. BUT, you're wasting fuel (even at around-town cruise speeds) and washing down the cylinder walls, to an extent, and needlessly increasing emissons. Using a tach is much more precise and eliminates getting it too rich as well as being easier. Have each screw out approx. the same number of turns. Warm up the engine and hook up a tach. Set each idle mixture screw for maximum RPM on the tach. Reset idle speed if needed. Next, turn one screw in until the RPM drops about 20-30 RPM. Repeat on the other screw. Set idle speed to specs. Now you know you're not wasting fuel because you know it's set just a tad on the lean side. No guesswork!

 

Ford Carburetor Forum. Carbs rule!!!!
This is a Ford 4100 carb forum.

Sorry wrong Thread.