2500 Rpms At Wot

[mikbry]

I have 2 of these Mercury 75 hp 2-stroke, yr 2003, used on a 18' american skiff. One runs great. The other one only goes to about 2500 rpm at wot. I've change the plugs, fuel filter and the carbs were cleaned about 4 months ago. My plans are to clean the carbs again and see if that helps. But if that doesn't what could be the problem.

My other 75 hp motor gets up to 5000 rpms no problems and the carbs were cleaned about 4 months ago as well.

Thanks in advance.

 

[CharlieB]

Re: 2500 Rpms At Wot

Either restricted fuel supply or weak ignition.

If it is a weak fuel pump it should respond be squeezing the primer while at full throttle. If that doesn't make any difference then test spark with a spark tester set to 7/16 inch. You want to see and hear a sharp hot blue 'crack'.

 

[mikbry]

Re: 2500 Rpms At Wot

I cleaned the carbs and took it out and it got up to 5000 rpms.

The problem now is at wot when I bring the throttle back down to 1/2 the motor is still at running at wot. I turn off the key and placed the throttle in neutral and it started like it was still at wot for about 5 seconds and came back down to idle.

If I run it about 4000 rpms and bring it back to idle it is fine.

What could be the problem-floats in carb?

Thanks in advance.

 

[CharlieB]

Re: 2500 Rpms At Wot

More likely your 'link and synch' and throttle cable adjustment are slightly off.

But if you question your carb float adjustment at all, then it could be a good idea to check them as once the carbs come off you should go thru the entire link and synch again to be double sure that it is absolutely correct.

 

[flatcat77]

Re: 2500 Rpms At Wot

make sure your throttle linkage is moving free and easy. its probably just backing down as it moves slowly back to idle. instead of snapping back fast with the cable.