Idle mixture question

rixm37 · Post by **rixm37** » Mon Jul 27, 2009 8:36 pm

Can someone explain to me how the idle mix circut works? Or maybe tell me where in which manual to find a good diagram. Maybe I'm losing it but when I went to adj the mixture the engine began running really rough like it was flooded and the mixture screw now seems to have no effect on the idle at all. Lots of black smoke and missing. I don't see how the idle mix screw could cause this but I never have taken one of these carbs apart before.

There is always the chance that something else broke at the same time as I was turning the screw... points? coil? gremlins?

Lifer · Post by **Lifer** » Tue Jul 28, 2009 3:35 am

It sounds like your idle mixture screw is too far out, allowing too much fuel into the engine. The smoke you see is unburned fuel. Screw it back in, and it should smooth out and you'll have no more smoke.

If you get it screwed in too far, the engine will begin to run rough again and you'll have to screw it back out a bit. "Happy medium" is about halfway between the two points where it begins to run rough.

Nickathome · Post by **Nickathome** » Tue Jul 28, 2009 5:20 am

I was told(with engine off) to turn the screw all the way in until it stops(don't force it after it stops). Once all the way in, back the screw out counter clockwise two to two and a half revolutions. Now start the engine, then begin to slowly turn the screw back clockwise until you can hear the engine start to slow down. At this point stop, and begin to turn the screw back counter clockwise slowly until you again begin to hear the engine start to slow. Now take note of how many turns you made from the clockwise point to the counterclockwise point. Now, turn the screw back clockwise half of the amount between the two points and you should be good.

This isn't exact but it works.

Lifer · Post by **Lifer** » Tue Jul 28, 2009 12:08 pm

Yep! It's been done that way with excellent results for nearly 100 years, now. Some things just can't be improved upon.

(well...you might be able to tweak it to a more precise degree, but you'd need a dynamometer and an exhaust gas analyzer to do it.

)

rixm37 · Post by **rixm37** » Tue Jul 28, 2009 3:36 pm

Thanks Lifer and Nick. I will give it another try and see what happens. It's 100 in the shade this afternoon so I guess I will wait until early tomorrow morning.
Rick

Nickathome · Post by **Nickathome** » Thu Jul 30, 2009 4:32 am

I forgot to mention, take a paint marker and make a line or dot on one side of the slot in the idle mixture screw to make it easier to tell how many turns you've made. If you don't do this it is more difficult to count how many turns you've made. At least that works well for me.....

rixm37 · Post by **rixm37** » Thu Jul 30, 2009 4:56 pm

Hi Nick
Well I spent some time with the M this last evening when it cooled off. I started with a cold setting of 2 turns and "got r a goin" after a few minutes. The excess gas fouling finally cleared up and I was able to make a few runs around the block. Seems ok now. I guess carbs are all different as when I adj my Bronco carb it reacts fast where as the M just started to load up and foul out the plugs. I never could stall it by turning the needle all the way in. Wierd.
Well we will see how it goes.....
Thanks again
Rick

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