I have a .90 Super Tigre that runs fine.......when I idle it down it will not stop. The throttle barrel is completely closed, I have checked the stop also. I sprayed the engine as it idled slow with wd40 to see if i could find any air leaks with no resulting rpm gain. I checked the rubber o ring and even installed the carb with a little rtv sealant just to make sure!
ANY IDEAS????????????

How important is it that the engine stop? Is there some club law you are trying to abide by? <G>

If the throttle barrel is truly closed ALL the way, then some air is likely sneaking in someplace...ie: Needle valve threads, etc.

MANY people would like to know how to keep their engines running! You have a very desirable "problem"!!!

Regards,

'Race

Backplate seal?

ZB

Hey ZB...

Could be I guess, but since the poster stated the motor "runs fine"...mmmmmmmmmm Probably not. A backplate leak is visible, as well as evident at other points in the RPM range. Most notably...going lean at full power.

Let's be careful here....because I can see it now.

75 posts from now, the poor guy will have machined the head, installed 50 different glow plugs, RTV'd everything but the exhaust ports and installed 2 pumps.

If it's a non-problem...let it go.

<G>

Seriously.

'race

I kinda know how he feels tho,,, I suffered with this on a GMS .47 along with "Mystery Flame outs at random".

ZB

Yeah...we ALL know how he feels.

I simply think we're discussing a non-issue. Pinch the fuel line...cup the spinner...motor stops...no problemo.

"Mai Penrai" as they say in Thailand.

Forget the convoluted "repairs"....I think the guys motor is fine.

'Race

sure its fine...........sure i can pinch the fuel line......sure i can grab the spinner.........but I DONT WANT TO!!!!!!!!!!!!

I put a piece of hose over the carb barrel pluged the fuel inlet and the throttle stop....dipped the motor and found air leaking past the front bearing.......now just gotta figure how to stop it.

THanks

Good luck!

They are supposed to pass fuel through the front bearing...it's how the front bearing gets lubricated!

RaceDog is right.....front bearing has to get fuel for lube, or else. I agree.....don't worry about it. Taxi up to your feet, and cup your hand over the spinner after you've shown the boys how low it will idle.....

Clair

This never seems to amaze me. I have a Tower 46 that will not shut off. I have never let it bother me but what really gets me is how low it will idle. You couldn't get a normal running engine to idle that low to save your neck.

The engine has never quit on me in the air, on approach, or on the ground unless the wind tipped it up and struck the prop.

So I'm happy.

Jim

Hey...my beloved MVVS is like that. It'll idle at about 12 rpm all day <G>. The bearing whir is louder than the exhaust. Actually had one guy want to know if it was electric.

Problem? Not at all.

Enjoy that LOW idle.

OK...what you've got with that ST is either a sealed front bearing that isn't sealing anymore OR a worn fit between the plain part of the crankshaft (in front of the inlet) and the crankcase.

At highish revs there's an average positive pressure in the crankcase which forces oil out the front bearing to keep it lubricated. At idle, the average crankcase pressure is negative so it can draw air past the front bearing and into the crankcase. In any engine where the clearances for oil are controlled properly there won't be enough air drawn past the front bearing to keep an engine running. Try fitting a new sealed bearing to the front (personally, if it's sealed both sides I'd remove the seal from the rear face to allow engine oil to get to it).

Try re-seating the carb into the mount. Press down firmly on the carb while tightening the pinch bolt. You could also add a little rtv to the o-ring gasket. It is possible to a small air leak at this point.