mercruiser 140 will not exceed 4000rpm

Mtl-Diesel

Petty Officer 3rd Class
Joined
Mar 15, 2019
Messages
91
Morning all! So my newly rebuilt 1984 140 will not go past 4000 rpm and 29-30 mph. Prior to having the engine failure I was able to hit 4400-4600 and 37-39mph.
It also seems to be missing "power" between 3000 and 4000rpm. Takes longer than I would call normal to get there.
Engine runs good otherwise. EST ignition, new plugs, wires, timing good, new fuel filters.
I'm scratching my head as I was expecting an amazing time out this year after the rebuild!
Any ideas?
I will also add that I am running the same prop I have always run.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,313
what engine failure? be specific

first, check your compression on each cylinder. a good/new engine is 150 psi per hole

what is your timing?

what is your fuel pressure?

when was the last time you cleaned the carb?

is your throttle opening fully?
 

Mtl-Diesel

Petty Officer 3rd Class
Joined
Mar 15, 2019
Messages
91
what engine failure? be specific

first, check your compression on each cylinder. a good/new engine is 150 psi per hole

what is your timing?

what is your fuel pressure?

when was the last time you cleaned the carb?

is your throttle opening fully?
Ya, a little vague. My bad.
Failure was due to timing gear missing a few teeth. Was replaced and new valves, head and block planned, gaskets all around.
Compression strong at 154 for all four.
When I checked the timing it was bang on what it should be but i'm having a block on what that is. I'll recheck this eve to confirm number.
Fuel pressure I don't know. How would I measure that? Can I rent the gauge required?
Carb was cleaned end of last season just before I had the engine trouble.
Throttle not opening is something I hadn't considered. I will verify that as well this eve.

Thanks for the quick reply!
 
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