low rpm 1992 Mariner 2-stroke 4-cylinder?

frozebubba

Recruit
Joined
Sep 20, 2017
Messages
1
Hello,

Engine serial number
OD261304

3rd hand engine with outboard jet, have been running for 10 years at ~25-30 hours per year.
Max indicated rpm used to be 5650 (equivalent to 5250 rpm on a harmonic tach, book max rpm is 5250).
Recently max rpm limited to 5400 and as the engine warms up rpm gradually declines to the point I am barely on step in a Alumaweld 18' Intruder.
This happens in non-carb-icing conditions.
While troubleshooting, removed the airbox cover and got my original rpm back, the motor runs better than ever before and fuel consumption was reduced by one-third.
Local mechanic puzzled but thinks it might be a cracked reed vale in a carb.
My solution, considering age of the motor is to just run it without the airbox cover (no difference in appearance of the carb inlet area with or without the cover) and enjoy the improved performance and fuel economy.

Has anyone else had a problem like this and what was your solution?
I may eventually drill holes in the airbox cover in front of each carb which is evidently a "fix" for older engines like this.

Thanks.
 
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