Roo Man

My Feedback: (1)

Have a used Magnum 91 4 stroke. New carb, New glow plug. Set carb at factory settings using 10% nitro fuel. Using electric stafter the engine pops like a magine gun, then it may or may not start. When it starts it runs fine at mid range an wot but won't idle. the engine will go into reverse often when trying to get it to idle. the transition from low RPM to wot is good.

Any help will be appreciated.

Gary

w8ye

My Feedback: (16)

I would check the cam timing to make sure that the center of the valve overlap point is around 5 degrees before top dead center and extends through top dead center.

Roo Man

My Feedback: (1)

Please explain valve overlap

Thanks Gary

blw

My Feedback: (3)

Take the rocker arm covers off and look at the the rocker arms as you turn the prop. Valve overlap is that point where both intake and exhaust valves are open at the same time. Jim is saying this should be about 5 degrees before top dead center. I take out the glow plug and put in a soft piece of wood so I can see top dead center when the wood reaches the top.

Roo Man

My Feedback: (1)

Thanks

Roo Man

My Feedback: (1)

I started at the beginning, first checking to see that the cam was properly aligned with the crank and it was, then re-set valve clearance, [ Dumb me on last valve set, used .04 thousandths instead of .04MM and also did not set the valves on the compression stroke] but got that all straightened out. I checked the overlap at 5 degrees BTDC and only one valve was open, exhaust I think, can't remember [old age will do that to you].

At this point I started it and after some tuning it runs pretty well. Will need some fine tuning but should be flyable come Monday.

Thanks to all for your help.

Gary