air fuel mixture screw

[MustangMatt1966]

what is the proper procedure for setting the air fuel mixture screws....my engine has been stumbling at idle lately and im wondering if this might be the cause..i checked the idle screw and its set right, but there must be something else wrong....i heard you turn them all the way until the car really stumbles than back them off half a turn or something like that? any help would be appreciated. thanks in advance

matt

 

[iskwezm]

you should really use a vac gauge. Set the idle so its smooth, adjust the idle screws to get the highest vacume.

 

[fvike]

If you want to do it by hearing, set it where the engine runs easiest. However, to get it right by hearing alone takes skill. You should do as iskwezm said, or perhaps with a C/O and lamda scoop in the exhaust.

 

[MustangMatt1966]

If you want to do it by hearing, set it where the engine runs easiest. However, to get it right by hearing alone takes skill. You should do as iskwezm said, or perhaps with a C/O and lamda scoop in the exhaust.

can you explain this further? so you are saying to measure it by testing the vacume, to set the correct idle mixture. I read in a magazine that these screws only control the mixture at idle and not under acceleration. am i correct in assuming this? thanks again,

matt

 

[dennis112]

can you explain this further? so you are saying to measure it by testing the vacume, to set the correct idle mixture. I read in a magazine that these screws only control the mixture at idle and not under acceleration. am i correct in assuming this? thanks again,

matt

Basically you try to achieve the highest vacuum possible at the desired idle RPM.

The mixture screws are provided primarily for idle quality. The have limited affect on off idle conditions. You can't tune them for driveablity. Driveablility issues will require specific changes to things like the jets (replacements) or adjusting the accellerator pump.

 

[MustangMatt1966]

Basically you try to achieve the highest vacuum possible at the desired idle RPM.

The mixture screws are provided primarily for idle quality. The have limited affect on off idle conditions. You can't tune them for driveablity. Driveablility issues will require specific changes to things like the jets (replacements) or adjusting the accellerator pump.

ok, so adjusting these screws will in no way hinder or tinker with the "uner acceleration" performance..they just adjust the mixture at idle and thus control idle quality...the car just stumbles at idle sometimes, not because its idling to low, but i feel its due to the mixture..i will play around some more and let you all know how it turns out

 

[dennis112]

ok, so adjusting these screws will in no way hinder or tinker with the "uner acceleration" performance..they just adjust the mixture at idle and thus control idle quality...

Correct, although if the screws were grossly misadjusted you could have some effects at higher speed. This does not sound like your case.

I would check the accelerator pump and make sure it gives a nice clean steady shot from the moment that you move the accelerator.

How long since you have had a tuneup (plugs, wires and points?)

Another thing, what do you have your engine timed at? If you are using factory specs you can usually run more timing which has a direct effect on performance.

Be sure to tell us what engine, carb,tranny, rear gear, and engine mods your currently running.

 

[MustangMatt1966]

now that i think about it, it has been a while since i have had plugs and a tune up done....hmmmm