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2005 50hp 2 stroke Run away reving when starting

T

tjt

New member
50 merc on my pontoon. Went to start today with shift lever in neutral slightly advanced. Motor fired and rpm went to max. pulling the shift lever back would not slow the motor down. HAD TO TURN THE KEY OFF. This repeated 2-3 times. Removed cowl and inspected the linkage. Both shift and fuel seemed free. Removed the air box and all carb butterflys were closed. All linkage seemed in sink with no binding. The carbs were closed when the engine was screaming. Went to the key switch and turned the key and pulled out on the key in case the primer feature was stuck in. Retried the key without pushing in and it started normal and idled fine. Any thoughts? The mechanical pieces seemed ok and nothing was loose or out of place, not sure how the primer functions other than pushing in to start. Thanks for your advise
 
What oil have you been using in this engine? Penzoil?


If you have an unexplainable run away it is usually caused by combustion leftovers on the pistons. They glow red hot and light off the fuel.

Put some Quicksilver Quikleen through the fuel system to decarb the engine.
 
Docksidemarineservices said:
What oil have you been using in this engine? Penzoil?


If you have an unexplainable run away it is usually caused by combustion leftovers on the pistons. They glow red hot and light off the fuel.

Put some Quicksilver Quikleen through the fuel system to decarb the engine.
Click to expand...

Have always used Mercuy premium blend oil semi-syn. Wil try the quikkleen. Thanks
 
Good to hear that you are using the recommended oil. I have seen an engine with so much garbage on the piston that it was revving past 6k rpm with the key in the off position. Only way to shut it down was to give it wide open throttle. Put a decarb mix through it and garbage was coming from the exhaust ports for a week.

Quikleen will correct this if it is the cause.
 
Got a 2006 115 Mercury 2 stroke. Want run over 4000 rpm. I have good compression and fire on all 3 plugs. Changed computer. Changed fuel lines. Mechanic puts it on computer it shows all systems working fine. This happened suddenly. Engine running fine one minute. Then not. HELP any suggestion. About to pull my hair out.
 
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