What are the symptoms of a bad diaphram on a YS 91 AC.


Pat

Either you will not get any fuel or it will be running out the carb when the engine is not running.

These are actually symptoms of the piddle valve that the diaphram operates is stuck one way or the other.

Jim

Thanks. Well I know thats not my problem. Whats happening is It is making this funny noise.It doesn't sound quit like a backfire but it will stall sometimes and other times it will run through it.If I richen it up it won't run fast and when I lean it it gets worse. Any Ideas would be appreciated

Pat

Allright, we know what it does now. Did you just get the engine and this is the way it ran? Did you have it apart? Did you crash it? Did you put it in a different plane? What fuel are you using? What prop are you using? What glowplug are you using?

Jim

I got it used, it ran good for a couple flights.I didn't take it apart,I didn't crash,It is in a new plane with new fuel tubing and tank.I am running coolpower 15% and a 14/10 prop. The plug is an OS type F. I'm wondering, could the timing be off 1 tooth. After thinking about it I can't be totally positive it ran right when I got it because it was over a year ago.

Thanks
Pat

Does sound like it.

To check the cam timing.
carefully remove the valve cover trying not to tear the gasket.
Undo the rocker arm stand.
Pullthe cam box cover off.
Push the exhaust lifter up out of the way.
Theres a mark on the prop drive place this mark in line with the crankcase casting on top.
There is a dot on the side of the cam that that must point directly at the cam follower.
Put everything back together and re-set your valves .002 - .004"

Then try it. good luck

Thanks alot.

Pat

Always keep in mind that all Y-S 4 srokes use the crankcase as a super charger. Under the valve cover is used as a plenum. So the .91 has two plenums. The air chamber or box on the back and then under the valve cover too.

Any leaks in these will cause you many heart aches.

If you take the airchamber off the back, you cannot get it back on properly without raising the jug and putting it back on then set the jug back down with the plenum going onto the carb out let.

Good luck,

jim

I'm thinking I have an air leak. The timing checks out, I tried to run it with every possible needle and regulator set up and it still make that noise and I can see big bubbles when running at slow speed and very small bubbles in the line at higher speed that the line that goes from the front of the engine to the carb.I think that might be making it go lean and backfire.When it backfires there are sparks between the nuts that hold the prop on!

Sounds about right.

The fuel should be under pressure all the way from the tank to the carb at high speed. There may be another problem beside just an airleak.

The problem could be within the regulator itself?

There is a forum for the Y-S engines next door here and you can at some point when you feel ready, post your problem on there. Within two or three days, Mr Dave Shadel himself will respond.

Jim