Crashtruk

I am wondering, how might I get my ST 90 to run better? It is mounted upside down in the cowl and won't idle very well at all.

Thanks in advance

gjesion

What glow plug are you using? You may wish to try an idle bar plug.

Regards,
Jerry

jetmech05

programable on board glow driver

TFF

The engine can be picky about tank placement; if it cant be perfected, you might need a pump.

Jester241

You must start off by telling us your how far below the centerline of you tank the centerline of you carb is. Tell us that,and we'll go from there.

Crashtruk

The centre line of the tank is actually 3/4" above the carby. Hmmm[sm=confused.gif]

JohnBuckner

My Feedback: (1)

Bingo Lower the tank and if that is not possible consider a side ways orientation. When changing to an inverted mount the Tank to spraybar relationship must remain resonably close to what works well with the upright engine. You cannot just invert an engine without lowering the tank. Many ARFs do not get this quite right either on some.

With the tank too high hydrolocking and syphoning can also become issues, Main needle setting become irregular and eratic and idle becomes difficult.

John

Crashtruk

Great info. You guys rock

Gringo Flyer

My Feedback: (18)

I'd put money on the tank being to high.

I have run that engine inverted and while it seems a little picky on tank location, once you get it in the right spot it is dead on reliable.

If the tank is even a hair too high it will run with the glow driver attached or above half throttle ok, but at idle it floods.

If the tank is in the right location you shouldnt need a glow plug with idle bar or remote glow. Those things might help but its better to get at the root of the problem.

YUKONFLYR

I have a SuperTigre .75 Inverted in a Mustang. Tank is way above carb centerline. The carb leaks raw fuel when I fuel up and the engine is fully enclosed in a cowl except for the top portion of the head. I have a K&B 4520 idle bar plug in it and it will run just as well on a K&B 1L.

I have no issues with the engine being inverted except for hydro lock when I get medevil with the afterrun oil.

Supertigres come with a very rich bottom end. I just keep screwing in the low needle until it runs right with the tank half full. Then fill it up and go fly it. Should have a good idle no matter what.

Richard

Crashtruk

As it turned out , the tank was 1 1/4 of an inch higher than the carby. I have had to install a smaller tank to fit in the fuse up higher. I will see how that goes.

JohnBuckner

My Feedback: (1)

That also put you at risk for hydrolock and can be insidious. For example after landing with a partial tank and someone carring the airplane with the nose down can start a syphon. Also just sitting in the sun with a full tank a tank can start syphoning on its own as the fuel expands heating up.

Its imperitive with any inverted installation to alway turn the engine over by hand first to check for a full or partial lock before ever touching it with a starter. This picture illustrates the carb feed line I always make accessable to enable hemostats to remain on the airplane after fueling and right up to the time of starting. This also gives a very conveinent place to fuel and pinch tune even with a cowl. For an inverted two stroke this is invaluable.

John

Crashtruk

I will do that. I had one of those fuel valves but that was too unreliable. Great info, great help

GRANT ED

I have had several planes with inverted engines. In each case the engines ran fine but were hard to start. One was bad enough that it was easier to flip upsidedown and start then turn it over. I'd suggest you adjust the tank as close to level as possible. Then I'd look at tuning and glo plugs to get the idle right.

Kimhoff

My Feedback: (22)

Put a Cline Regulator on it.