Posted by JimmieD on Thursday, November 04, 2004 at 2:52PM :
In Reply to: Re: Cold weather and Carb posted by David Sherman on Thursday, November 04, 2004 at 12:40PM :
Hi Shawn,
I can't remember what carburetor you have but it could be a part of the idle mixture adjustment that is contributing to the problem.
On almost any carb there are mixture adjustment screw[s] at the base, and also the idle speed screw at the throttle linkage, plus lever operated fast idle cam at throttle shaft.
For any carb I have seen the adjustment procedure is very similar on idle mixture. Set curb idle speed correctly with engine warmed up, using idle speed screw at throttle linkage. Now open up the idle mixture screw[s], usually at base of carb, until you achieve the highest rpm. Do this on one idle mixture screw, then reset curb idle speed to normal, then do the same with the other mixture screw if there's 2 of them. If not 2, then do that for 1 mixture screw.
Next you lean out or tighten in that mixture screw until the engine rpm's drop about 20 rpm's. Obviously a tach is handy, but you can also just listen for a VERY slight drop.
That is called 'Lean Best Idle Mixture' and it will work for 99% of all your driving.
If you have a manual trans you can find that point that it drops, after finding highest speed, and then turn it open just a hair bit farther, back towards the higher speed or richer mixture and leave it there.
The reason for a difference with manual trans is that slightly higher speed helps the synchronizers in the transmission when you shift gears, much like double-clutching, or watching the tach to bring rpm's to match the next gear.
If speed doesn't change much when adjusting mixture, get out the spray can of carb cleaner, remove mixture screw[s] and blast the hole real good with the plastic tube down inside [watch your eyes please]. Before removing mixture screw[s] gently turn them all of the way in, counting the number of turns, and then reverse to remove. That way you can reinstall to the exact same mixture after cleaning.
You should also check the position of fast idle cam, there on the end of throttle shaft, which the curb idle speed screw should rest against at cold startup. Check it cold, and then set the choke by depressing the throttle pedal fully one time. See if it caught the fast idle cam for its resting place. Then start the engine without touching gas pedal again, and look under hood to see if it's still on fast or high part of that little cam. If not, a simple [?] adjustment can be made to get it to sit there at cold start.
Also check to make sure the choke is staying closed at warmup for as long as it should. There are adjustments, as you know, to set that correctly.
JimmieD
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