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1998 25 yamaha 25smhw3. I have been searching the internet endlessly to find a fix for an issue with my motor. The motor idles fine, have fire on all 3 cylinders, 110 compression all cylinders, i cleaned the carbs 3 times and changed the fuel pump gaskets. The motor will jump out of the hole but when it get to wot it seems to have a miss and won't open up like it should. it almost feels like when you hit the limiter on a truck or car. After running it I take the spark plugs out and they seem to be dry. any help would be great. I am not sure if it is a fuel problem or electrical.
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Maybe check the fuel pump....remove pump from engine but leave fuel hoses connected, then pump primer bulb...no fuel should come from hole/port on back of pump. These pumps can and do develop holes in diaphragms.... -
The fuel pump is connected to the carburetor i changed the diaphragms. I may have put them on backwards. ill check it this weekend.Originally posted by robert graham View PostComment
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My mistake...thought you had the crankcase pulse type pump....you're probably O.K., pump-wise....Comment
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use a timing light to monitor the spark on the different plugs at the problem RPM and check the timing too
If spark and timing of the spark is OK then you are left with a fuel problem.
I had a similar high speed miss on my C40TLRX that turned out someone drilled out the main jets causing it to be too rich to burn the fuel properly.
Also the crankcase re-circulation valves were bad in my motorComment
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