Propwash in Pa

Both myself and a fellow club member are experiencing the same problem with our Magnum 90 4-strokes. They both have full RPM range, but will only idle down to a certain point then actually increase in RPM. Neither will actually shut off with the kill switch. High end is set properly (just a tad rich). We do not think it is a mechanical issues as adjusting it seems to make situation worse. We were thinking that the low end is too lean thus increasing RPMs. After adjusting the low end to make it more rich, the problem still exists.

Any thoughts??

w8ye

My Feedback: (16)

The bottom end is too lean

This engine has a low speed throttle stop that you you need to screw out just enough to get the throttle completely closed for shut off.

Will the engine shut off?

Will it idle at a low speed

Propwash in Pa

It does idle although it is a little fast (not too bad though). When the kill switch is pressed, the RPM drops and then quickly raises to faster than the original idle.

w8ye

My Feedback: (16)

I have never experienced this with my 4 Magnun four strokes.

There must be an air leak somewhere around the throttle barrel?

I would get the engine out of the plane and onto a test stand so I could see what was going on?

Enjoy,

Jim

johnS555

My Feedback: (27)

B8ye has hit it on the head, you have a leak around the barrel if it will not shut off.....

Good Luck
John

johnS555

My Feedback: (27)

Or, possibly and intake manifold leaking..like he says ge it on the bench and check for the carb operation, when the carb is pulled on to close the barrel...........cheers........John

johnS555

My Feedback: (27)

Last thing and I will get out of your hair, beings I am old and can`t think of all these things at once======possibility of air leaks around the seals on the 2 needle valves........I`m out of here........good luck again.........

Propwash in Pa

Okay, is there any trick to finding the leak. Can it be heard or seen? Is this something that the manufacture should fix?

Thanks for the help.

Hope all get to enjoy a Newyear's Freeze Fly.

Flypaper 2

Take the carb off. Put a piece of fuel line on the fuel inlet. Put the carb under water. Blow on the fuel line. Bubbles will show where the air leak is.

GaGeeBees

My Feedback: (23)

Before you go through all that, take the cowl off and look down the barrel of the carb to see what's happening when you hit your kill switch. You may be surprised to find that the barrel of the carb is rotating the wrong direction (opening rather than closing). Do what you want but I'd verify that before disassembling the engine and putting my carb under water. I have many Magnum engines and have seen this before and every time it happened to me it was something in my radio setup/mechanical linkage. Just my $0.02 worth. Good luck and let us know what you find.