Motor won't idle, but runs well off idle?

[WRecker]

I'm hoping some of you tuning genuises out there will think of something I didn't. My '88 Tecate-4 has a stock motor (very healthy, with 140psi cylinder pressure), aftermarket pipe and silencer, and a Keihin PJ carb. I usually run av-gas at 40:1 with Maxima Super-M. Bike runs excellent at all speeds and starts with a half-hearted kick when cold, sometimes a little more effort required when hot. But, it won't idle (just dies)! Here's what I've done so far:

~Disassembled and cleaned carb 3 times, paying special attention to the choke and pilot circuits. Both are clean and wide open.
~tried pilot jets ranging from #42 to #58.
~air filter meticulously cleaned.
~drained fuel tank and cleaned petcock to remove any sediment.
~removed, cleaned and inspected reeds (no cracks and warp is well within service limit).
~checked for air leaks around base gasket and reed block using starting fluid, no apparent change in engine speed.

The two things circling in the back of my mind are float level (although it would've had to drastically been lowered somehow to expose the pilot jet, and the bike isn't starved for fuel in the top end), and timing. I had an issue with my Ricky Stator not too long ago (ignition coil gave up, and the folks at Ricky Stator graciously fixed it and sent it back gratis), and since I don't have a timing light for a 2-stroke, I put it back in and made several test runs with the bike, adjusting the stator in small increments each time 'til I thought I had the best performance through the rpm range. Is it possible that the timing is still off enough (retarded perhaps?) that the motor doesn't want to idle?

Any help would be GREATLY appreciated!

 

[David Trustrum]

Um dude -you don’t mention that you adjusted the idle speed screw? Does it run out of adjustment?

Idle for how long? 20 sec or not at all?

 

[John K]

"stock motor" ..... why are you running avgas?:eek:

 

[WRecker]

Sorry I've been absent so long!

First, David, the airscrew is approx. 1-3/4 turns out. It won't idle at all, unless I stay on the throttle, not even for a few seconds.

Second, John, the reason I'm running av-gas is because of the high compression of a stock Tecate-4, plus the fact that I run this quad primarily at the dunes, wide open, on hot days. Also, with the inconsistent quality of pump gas, and the strictly regulated quality of av-gas, I think it's a better choice. If I could afford it, however, I would be buying VP race gas by the drum.

A possibility that I have yet to investigate (been too busy riding and wrenching on the WR!) is that the crank seals are old and dried out to the point where they're leaking air (and a little oil from the clutch side). I'll keep you posted.

 

[David Trustrum]

The idle screw not the airscrew. The one with the external spring that bears on the underside of the slide adjusting the height of the slide at rest & hence the idle speed.
?

 

[WRecker]

Sorry, brainfart there.

The idle adjust (which, on some Keihin models doubles as the choke knob) has virtually no effect on the idle. If I crank it all the way out (which should be highest idle), the only effect it has is the rpm settles down a little slower after revving, but still won't idle, just drops off and dies. With the knob turned all the way out, it also negates the use of the choke. This is one particular feature of the PJ carb that I HATE! What was wrong with the old external screw that raised the slide?

Since this type of idle adjustment does nothing else but regulate an air passage, I've paid very close attention to be sure that it is not blocked. I've also checked to make sure all vents and hoses are not blocked.