Adjusting idle mixture screws, which gauge?
 

Hey guys well idle mixture screws have always given me trouble.(i just cant get them right)Recently a friend of mine messed with my mixture screws and now i have horrible bogging at low rpms.

What i want to do is buy a vacum gauge and go by that instead of trying to set them up by ear. With the gauge i figure i could go by the reading and attempt to get maximum vaccum.

Ive been looking through summit and theres just so many different types of gauges that im not sure which would work best for what i want to do, is there any additional equipment that i will need to get the best results? Im runnin a Weiand stealth intake.

Any help/input apreciated.

First, some basics. Idle mixture screw adjustment is almost impossible to get to affect off-idle response. Something else is going on. However, improper ignition timing can cause off-idle problems, among other things, so before you mess with the carb, get the timing set properly.

Now, a vacuum gauge is a good thing to have. You don't need to fuss over what to get, though. Most any auto parts store will have an inexpensive diagnostic gauge that will do the job. It'll have a piece of rubber hose on it for you to connect to a manifold vacuum source on the engine.

Re: Adjusting idle mixture screws, which gauge?
 

If he's running the computer controlled q-jet, dickering with the mixture screws will throw it way out of whack and could cause all kinds of off-idle and throttle transition problems.

Re: Adjusting idle mixture screws, which gauge?
 

From the research ive been doing ive read that an improper idle mixture can
cause bogging hesitation and backfiring. I am almost positive that when my friend messed with my screws it set the whole thing off because the car was fine before then.

The carb is a holley 4160 so no quadrajet. But is it really that farfetched that
the mixture screws are causing my bogging? My timing seems fine it has a new hei dizzy and no pinging is present. Although i havent checked the exact setting.( just bought car)


I should probably mention the bog is at low rpms only

Re: Adjusting idle mixture screws, which gauge?
 

I dont know what your definition of off-idle response is, but back when I was tweaking things, I had turned them 1/4 turn one direction and the car seriously ran like a donkey. Throttle response went to complete garbage and it bogged and ran like crap. Turned it 1/4 turn back the other way, and it ran fine again. I was trying to get it to run better in the extreme cold of mid-winter nights.

You have to have other things pretty messed up in order for the idle mixture screws to cause, or solve, those problems.

First make sure the timing is set properly. Then go to the Holley sticky in the top section of this forum and go through those steps.