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dead cylinder

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bobbykey

New member
I have a ns90a its got spark, gas and compression but #1 (top cylinder ) cylinder is dead.

compression #1 135 psi, #2 133 psi , #3 134 psi

When I pull plug wires on #2 and #3 rpms drop considerably and and when I pull #1 it seems to make rpms speed up a little.

Ive changed plugs and cleaned carbs twice.
 
Or, as Elvin mentioned on the other board... it is remotely possible that you have a twisted crankshaft.
 
How strong is the spark on the dead cylinder?----Will it jump a gap of say 3/8" or more ?---Put boat into the water , motor in gear ---go to full throttle and shine a strong flashlight into the carburetor bore.---You do this to observe / compare the fuel coming into the airstream at the venturi.
 
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if I get my hand close to the bottom to carbs I can feel some suction but the top one has no suction I can completely cover it with no change in the motor and when I remove my hand the throat is filled with gas
 
The carburetor float valve is leaking.------------And the lack of suction may be a crankcase compression problem ( reed valve ??)
 
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