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08 Mercury 50HP 2 stroke fuel problems

D

danbus47

New member
Original owner died shortly after purchase and the boat sat up with 10% ethanol for about 6 months. It ran fine on trial but the 3rd time I took it out it wouldn't crank. I took it to the original dealer and they cleaned the carbs and educated me about boats and ethanol. It performed fine until I let it sit for 4 months last winter with a full tank of non ethanol gas. The first trip this spring it cranked right up but idled a little rough and wouldn't accelerate over 2700 RPM. Any more throttle would kill the engine unless you were pumping the bulb. I ordered a Seloc Manual and began working on it. First pulled the pickup tube out of the tank, clean with no obstructions. Removed and inspected lines from picup tube to engine, no problems observed. Next removed inline filter, clean as a whistle but I found the line from the filter to the top carb had a severe kink. Replaced lines from fuel pump to filter and filter to carb with no kink. Cleaned and put kits in carbs and fuel pump. The carbs showed no sign of gumming but the rubber coating on the pump inlet side diaphram was brittle and flaking off. Between the kink and the diaphram, I felt sure the problem was solved. Took it out this weekend and it cranked right up, idled smoothly but was a little rough under acceleration. It will plane out, reach 4200 rpm for about 300 yards then it would die. I repeated this for about 45 minutes with no improvement. Needless to say, I'm flabbergasted. Any suggestions would be greatly appreciated. BTW, engine has 38 hrs running time.
 
Have a helper operate the manual fuel pump and see what happens at full throttle.------------Are you sure that there is spark on all cylinders ?--------Full throttle RPM should be in the range of 5200 / 5500 RPM.-------------Make sure it is not a fuel issue or oil injection issue.--------------Blockages in a carburetor means, less fuel and less oil going into a cylinder !
 
Not sure I was right about venting not being the problem. This is a Perko fill and venting system with surge plug. The system doesn't appear to vent outside of the enclosed tank. Am I missing something?
 
If you remove the vent line at the tank can you blow air thru it backwards? If not it's stuck...replace?
 
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