Motor won't run above 1500-1800 RPM

[5150abf]

I have a 1981 Evinrude 50 ,2 weekends ago it ran fine, last weekend I put it in, it started and idled normally but wouldn't go over @1800 rpm,changed plugs with no effect.
Idles fine comes just off idle in gear then just stops accelerating at 1800, more throttle just makes the exhaust sound flatter but it doesn't surge cough or sputter.
I fixxed several wires that the sheath was cracked,thinking it may be a short,took the carbs apart and soaked in Sea-Foam then blew out all the jets,took it out and it ran fine, jumped up on plane for 40 yards then back to 1800rpm.
I have done all the normal trouble shooting, has spark, gas tank vented, has fuel to the carbs,even checked compression,140, cold -both cylinders.
I obviously missed something but what?
Could a low battery cause this,1 of the teminals was loose, wouldn't start,tightened the terminal but the boat only ran for @ a short time then I hit this problem.
Any help is greatly appriciated

 

[Molaker]

Re: Motor won't run above 1500-1800 RPM

Sounds like your timing is not being advanced with the throttle. Some linkage may have let go. Check the throttle/timing synchronization.

 

[5150abf]

Re: Motor won't run above 1500-1800 RPM

Did that,at least at the linkage, as the throttle comes up the timing advances and you can advance it by hand which of coarse makes the motor scream without adding throttle.
I may go out and check that in a bit,checked timing the other day and it was 2-3 degrees BTDC at idle as it should be ,I work for a boat company and one of the mechanics told me how to check the full advance so I will do that later today and make sure it is advancing like it should.
Could something have come loose under the flywheel maybe?
Very strange problem it is, thanks

 

[clemsonfor]

Re: Motor won't run above 1500-1800 RPM

Clogged high speed jet, maybe?

-Nate