Loss of RPM's

[CheckmateGator]

I have a Merc 90--Only work is Wiseco pistons. I was running 6100 RPM wide open last year. Slowly I have lost RPMs since. Yesterday I ran it and at wide open I am now at 5300. Anyone have any ideas?

[CheckmateGator]

I have a Merc 90--Only work is Wiseco pistons. I was running 6100 RPM wide open last year. Slowly I have lost RPMs since. Yesterday I ran it and at wide open I am now at 5300. Anyone have any ideas?

[JW]

check the easy stuff first. Do a compression test, you may have a cylinder going down. While the plugs are out, take a look. If one plug is real clean and just wet, maybe that cylinder isn't firing. Could it be a blocked passage in a carb?

1995 2100BR/1995 225 Promax/23" Tempest

[CheckmateGator]

Thanks for starting points. I have a suspicion it is a carb problem, but I have no experience rebuilding carbs. Looks like it's shop time!

[Chris]

Mercs are famous for stator problems.

But I'm with JW, start with the compression test, and see what the results are. Then proceed from there.

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[175checkmate]

With the engine shut down, pull the cover and air box so you can see the carbs. Now pump the primer bulb. Do you have fuel running out of the carbs? If so you have a bad seat in the carb and its flooding. Could also have a bad primer bulb, or air leak on the suction side of the fuel pump. I would also have a look at fuel pump. I had all of the above. Could not rev under load. I went to an electric fuel pump

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1975 Checkmate Tri-mate 2, 2.4 200+