90 hp 2 stroke stumbles from 3000 rpm up

G

geo whifl

Recruit
Joined
Apr 19, 2011
Messages
3
My 2005 Mercury 90 hp 2 stroke idles well, runs up to 2500 rpm ok, but stumbles above 3000 rpm.
Carb's adj. don't help, changed to external gas tank, new gas filter, new gas, new plug wires, engine runs rough above 3000 rpm and dies higher than that. Strangely if you disconnect any one plug wire
at a time the engine now runs up to 4000- 5000 rpm with no problems.
What to do??? replace ????? Can't check rpm at engine block so using console gauge.
Thanks for any help,
George
 
C

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: 90 hp 2 stroke stumbles from 3000 rpm up

Double check spark plug wires

Use an inductive timing light and check timing on EACH cyl, you won't find a timing mark for 2 & 3 but should find the original mark about a third way around the flywheel from the pointer.

It the problem RPM range does the light remain on? Or go out, indicating a mis-firing of a cyl.
 
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