redhawkk

Hello,

I have a 1967 Mustang coupe with a 1988 Mustang 5.0 H.O. engine conversion with only about 50K miles on it. It is set now up with an Autolite 4100 carburetor on it. I've just rebuilt the carb (not the first time as I ran it for many years on a 1966 convertible). In any case I set the floats per spec (1/2" primary, 5/8" secondary).

It now runs and drives great, BUT seems to idle too rich, as I smell excessive exhaust. No sign of any smoke though. I am wondering if the float levels should be set differently. Since this 1988 engine has roller cam and was normally fuel injected from the factory, maybe the standard old 289 carb adjustments need to be tweaked.

My only complaint (actually my wife's complaint) is that "it stinks".....!

I'm wondering if anyone here has an idea of some additional tweaking of the carb adjustments that might help...?

Thanks.

Joel5.0

If a WB is not an option, just make sure you vacuum calibrate/tune it .

67mustang302

It should have an idle mixture screw(s). I haven't used the Autolites, but I know they are very reliable and run nicely. If you have mixture screws turn them in until it starts to run a bit rough, then turn them back out until the engine smooths and add about another 1/4-1/2 turn out. That's how I mainly do it, then fine tune it if there's any minor part throttle off idle hesitation. You should also post in the Classis section if you haven't already, lotta guys there have experience with the Autolites

redhawkk

Joel, I'mnot familiar with your term "WB"... what's that?
Thanks for the vacuum calibrate link..!


67mustang, I should have mentioned my experience with the idle screws. If I screw then in (lean) I can make the engine shudder, and likely kill it if I screw them tight (didnt' try). If I screw them out (richer) I do not reach a point where it ever starts to shake. Now, many years ago I recall reading that this situation indicates a particular problem, but I cannot remember what it was...! It may have been a failed power valve -- but I have replaced that (twice actually, recently, just for that reason).

Just today I went back to my copy of the original Ford service manual for the 67 Mustang and it has a pretty good coverage of the 4100. Interesting that it shows there is an idle circuit in the secondary section as well as the primary. There is also a "fully closed" adjustment description of the secondary throttle butterflys that's not quiet closed -- as if it allows some air flow thru the secondaries during idle. I didn't expect that, but it could explain the weird action of the primary idle screws. It too much air was pulled thru the secondaries, perhaps the primary idles screws could be wide open and never produce a rich enough charge to choke it. I will have to play with that a bit...

One thing for sure, there is no hesitation on coming off idle or anywhere that I could feel driving it. That probably indicates I could reduce the jets a size or two. Only the standing idle seems to have a problem.

Thank for the suggestion about the classic section. I just found this forum this morning, so not real familiar with it yet.

Gary H

It shouldnt shudder as you turn the screws out. Hooka vac gauge to it and turn the mix screws out till you get the highest reading. FWIW, an old autolite 4v carb I ran had worn steps in the idle mix screws so it made the idle mixture hard to get right.

turt

I have alot of experiance tunning carbs. This post may get long winded. Im not sure I read your post correctly. Is this the first time this carb has been on this motor? or has it been on this motor before with no problems. Im going to answer like this is the first time its been on this engine. The first adjustment should be done off the motor. this adjustment is for the idle speed screw(the throttle blades). It is importaint to NOT have them open too much so that tip in fuel is NOT added during idle. If your not sure on the correct position, check the carb specs or adjust the blades fully closed the readjust them open just a tad. Then mount the carb on the motor. Fully screw the idle mixture screw(s) in then back them out 2 and 1/2 turns. This setting should get the car started. If not, try adjusting the idle speed screw to open the blades a bit more BUT RECORD THE AMOUNT YOU TURN THE SCREW. This will alow you to return this adjustment back to what it was. If the initial setup did start the car then its time to adjust the idle fuel mixture.One at a time, screw the idle screws in untill car starts to stall then back it out just untill it runs smoothly again. Do the other screw the same way. This should be your best setting, however most of the time it isnt. If it smells like raw fuel, then the mixture scews should b tightened a hair. If on off idle acceleration there is a stumble then it may be too lean. The speed screw, theoretically, shouldnt have to be adjusted too much. On that carb I dont think there are any air adjustments so what used to be done was drill a small hole in the throttle blades to get the idle speed up a bit (NOT OVER ADJUSTING THE IDLE SPEED SCREW). There are several fine tunning procedures for a carb. If this is the first time this carb is on the motor then it may need some drastic adjusting. As for your float adjustments, the only way it would come into affect at idle would be if it is way too high or way too low. You can try lowering it a bit but if it was too high you would probobly run into other problems like fuel leaking at carb. Good luck.