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Smoking and misfiring 2002 90hp Mercury

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Danny001

New member
Hey guys, I recently got a 2002 90hp two stroke mercury. I have just bought it and had a new thermostat, spark plugs. It starts good however it smokes a fair bit and will misfire causing the outboard to die at idle. I have done the timing and still not much better. Carbs are also very clean. When it warms up it doesn't misfire as much at idle until you give it some throttle where it will smoke heaps and run rough and when letting go of the throttle it misfires and turns off again.

Does anyone have any idea?
 
Excessive smoke can be caused by a faulty 2 psi oil check valve or an internal leak in the oil pump that is dumping oil into the crankcase. Is the engine leaking oil on to the ground?
 
I currently boat seldom. As a result, my 115 2 stroke 2002 Mercury takes awhile to get gas into the combustion chamber....and I know how to start an engine. While trying to get fuel to the chamber, as long as the crankshaft is turning, the oil pump is pumping oil into the fuel line....whether fuel is there or not. As a result, initial ignition is a cloud of smoke and misfiring, rough idling and all that.

I undid the mounting screws and one hose to get the oil pump out, pulled the drive gear/shaft out of the pump and put things back together. I then premixed my fuel at the 50:1 ratio. Walla, no more starting problems, no more missing, smoke cloud or any of that.
 
We have a put a new fuel pump and hoses and still no fix. I understand that when starting that oil will get pumped in, and yes starting there is a cloud of smoke. However even after 15min of idling it will still misfire ever 2 min or so. and when reving low rpm it will run quite rough and smoke suggesting possibly a bad CDM? however we have a done a basic spark test and it seems all good. Ive checked the wires to the regulater too, as some people said that they had burnt yellow wires and thus caused a simialar issuie, however they are fine and everthing looks good. Maybe its the fuel to air ratio?
 
Have you looked at the carbs? A bad float needle? I believe that carb has mix screws that could be set to lean? You could have a leaking primer. The oil pump is probably not your problem. That motor has a mechanical pump. The reason 2 strks smoke at the start up is pretty common. The fuel in the mix in the carb evaporates and leaves the oil, thus you have an initial rich mix going into the motor. When the motor is turning over the fuel pump and oil pump are BOTH working
 
The carbs look like they had just been taking off and cleaned before i bought it, I still did take one off to see and was very clean however didnt check floats or possibly a blocked needle, however it still starts super easy but then misfires and dies. I might take the carbs off and have a good look over. There is a screw on top of each carb however some people say that its for idle adjustment. I wanna be certain what they do before playing with the carbs to much.

Thanks for your help.
 
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