bigbobed

I'm just starting my 3rd tank of breakin. All of a sudden it wants to start backwards only. It's almost like it has jumped timing. When I cover the intake to prime, it pulls fuel and then at the end of the intake cycle it pushes fuel back down the fuel tube. The intake valve is not completely closed until after bottom dead center.
Any ideas?
Thanks,
Bob

ajvpb

My Feedback: (3)

That sounds pretty serious. The first thing to do is check the valve adjustments ( the manual will say how to do this). If that doesn't work, it sounds like it has almost jumped timing, and requires a thurough looking into. I'd say the valve retaining nut probably backed off a little bit, I'd check that first. Good luck

Alex

Motorboy

Same i has Magnum 52 FS..
If valve adjustments are ok, please check valveseat are tight.

I discovered the valves was not tight enough. Then i lapped the valves with grindingpaste. Now it run well. [&:]

bentgear

Starting with an electric starter or flipping it?

If you are flipping it you may have to:
Start leaning it out a little. Overly rich mixtures tend to start backwards more easily.
Try flipping it backwards against the backside of the compression stroke.

I doubt it has jumped time, you would have more problems than you do now. It would be a good idea to check the valve lash, but I think this should be done before you ever crank it the first time.

Ed M.

Motorboy

It is normal for 4 stroke engines.

The intakevalve begins to open before top dead center and close after bottom dead center.
Exhaustvalve begins to open before bottom dead center and close after top dead center.

Between period when intakevalve begins open before tdc and exhaustvalve begins to close after tdc, it is overlap to improve effect to drawn fuel mixture from carburator to cylinder..

Jens Eirik

bigbobed

I'm starting with an electric starter. Valve lash seems to be correct. It occurred to me that the problem started after I removed the bottom part of the carburetor. I was adjusting the throttle servo and inadvertently loosened the throttle arm by setting the servo end point too far on the full throttle end. Easier to remove the carb to tighten the arm rather than removing the engine from the plane. Can't imagine how that could cause this problem, but you never know.

bentgear

OK, well, does it start running the correct direction and then kick back and start running backwards?

Ed M

bigbobed

It doesn't actually start. It kicks back against the starter, sometimes hard enough to loosen the prop nut. Prior to removing the carb, it was running pretty good. I had the top end set up and was working on the idle. Couldn't get it to run below about 3300 so ordered a hotter plug and was waiting for that.

TLH101

My Feedback: (90)

Sure sounds flooded to me.

bigbobed

Removed the carb one more time to make sure I hadn't turned the spray bar or something else stupid. It kicked back one time and then started. Went thru several full throttle/cool down cycles with no more problems. Go figure. Looks like it's going to be a pretty good engine. Tops out at 9600 which I backed off to 9400 and idles at 2300-2500. If the wind ever backs off, I am out of excuses and will have to go flying.
Thanks for the help.