125M won't idle but runs fine?!

[mrcribbs]

So after a week of owning this '84 125M I decide to clean the carb to see if I can get it to idle. Needless to say the carb was filthy and the slow (pilot) whatever you want to call it was totally plugged. So I get it spotless with all passages and jets clean and blown out with compressed air and now it still won't idle. When I turn the idle screw in it will increase until it gets to a point that it idles too high and takes a while for the RPMs to come down after hitting the gas. If I turn it out where it won't idle it runs fine.

Current settings
Needle clip one down from the top groove. (Stock position I believe)
92 Main jet (stock)
Stock slow jet
Fuel Screw 1 1/2 turns out (tried it all over, in and out with no help)
Clean (new) air filter
Float level at .400"

I also just adjusted the valves 0.003" I even checked the timing marks and the cdi pickup gap. Everything looks good. 150 PSI compression.

Help!

[Xpress]

There should be another adjustment screw. Also, check for air leaks, that can really mess with idling.

[mrcribbs]

I've adjusted both the pilot screw and the throttle stop screw. I'll check for air leaks, more than likely it would be the carb cap leaking?

[jensenracing77]

i am wiling to bet that it is the advancer springs. i am seeing this problem come up on here more and more. you have described the symptoms perfectly. i need to make a thread on this and what to look for. the springs ware out or brake and the timing advance will jump all over the place at idle. after you rev it up a little it will run perfect because it has advanced to where it should be. the problem is that the springs are not available and you have to get a new advancer. i have wired the advancer so that it won't move and get it to idle great but it has no top end. the advancer is behind the cap on the head that has CDI on it. it mounts to the cam. easy fix but i think a new advancer is over $100

[mrcribbs]

Thanks! I will check it out. My parts motor has a good advancer on it.

[mrcribbs]

Swapped advancing unit, no change.

Replaced gaskets on both ends of the intake tube and o-ring at the front of the carb, no change.

Going to make a new gasket for the carb top tomorrow at work... running out of ideas...

[mrcribbs]

For comparison, it acts like a two stroke does when the pilot jet is one or two sizes too small.

[EarlyBronocGuy]

Are you sure the throttle cylinder is moving freely in the carb tower? It may be getting stuck before it goes all the way down, or the spring under the cap is weak or broken and not pushing it all the way down, or the throttle cable is binding or stuck. Pull the intake tube off and shine a light in there, make sure the cylinder drops all the way down across the venturi when the throttle is closed. Don't forget the spring clip that secures the needle, without it the needle will be free to bounce up and down.

[goump1995]

When you clean a Carb's Jets , never run a needle through the holes of it , It scratches the need and screws up the Carb.,Always use a Carb cleaner or kit. If you have already cleaned the jets with the needle the you will have to buy a rebuild kit , OR! You might have not reset the jets right.

[mrcribbs]

As jensen said, it is the advancer... I tightened the springs up a bit and it runs great now. Looks like I'll be picking up a new advancer soon!

Thanks for your help.