itspuddingtime00

I have a little over a gallon on a Magnum 91 4 stroke, and the low idle suddenly became erratic and engine stalls out if not run on higher RPM. No settings were changed from the last time I flew it, and it was running just fine. The low speed needle is very touchy, and it will not seem to hold a tune. My first thought was that the low end was either too rich or the glow plug was fouled, but neither of those solved the problem. I also tried flushing the carb and checking for air leaks in the fuel lines. The engine is hard to start, and when it does start, the idle will start out really high, but if you try and lower it at all, it will cut out. Also, as you advance the throttle, the transition is extremely choppy. When it gets to WOT it clears up, but the low and mid range rpms are choppy. I am beginning to think that there is an air leak somewhere, just because it will not hold a tune, and I have gone through all of the basic things that I can think of. If anyone could offer some advice it would be appreciated. Thanks.

stagger wing

Hi,

have you allready tride to messure the valve play?
I had a simular problem and I have redone the valve play. So the problem was solved.

kind regards

itspuddingtime00

No, that is one thing I haven't done. This may be kind of a stupid question, but how exactly do you set the valve gap. Is it between the rocker arm and the actual valve stem? Do you just take a feeler gauge and adjust the rocker. And I'd also assume that the valves have to be completely closed, but please correct me if I'm wrong.

Norm Nestie

You're right the valves should be closed, engine cold. Clearance should be between 0.04mm and 0.10mm. If tou know someone with an OS 0r Saito 4c they may have feeler gauges. Otherwise a kit is pretty cheap. Would be interested in knowing how you solve it.

itspuddingtime00

I actually already have a set of feeler gauges and 2 other 4 strokes, both being Saitos. I know the recommended valve gap for Saito is .004in but I'll look in the magnum manual to see if they give any specs.