Not running at full throttle

[Sw23!]

I have a 1988-1989 40 hp evinrude that is not running full throttle. I have replaced all fuel lines, cleaned the carbs, replaced the carb gaskets, it works perfectly in reverse. Once it reaches about 2to3 thousand rpms, it starts to surge. I am not sure if this is a fuel issue or something different. Any info is helpful. I have also done a compression test and both cylinders are in perfect shape.

 

[airshot]

What is your definetion of perfect shape? Numbers?
Did you do a complete rebuild of the carbs and set them to factory specs as noted in the rebuikd kit or just clean them? Fuel pump pressure?

 

[Sw23!]

What is your definetion of perfect shape? Numbers?
Did you do a complete rebuild of the carbs and set them to factory specs as noted in the rebuikd kit or just clean them? Fuel pump pressure?

Each cylinder has 140psi for the compression test, I did not do a rebuild on the carbs and I am not sure what the factory specs are. I did replace the gasket on one of them and clean them out completely. I do not know how to find out the fuel pump pressure either. I have tried all of the basics I know but have not had any results.

 

[airshot]

A simple test is to squeeze the ball when it stumbles, if it gets better then fuel flow is an issue. Carbs need to be close to perfect in being clean and adjustment. Often the rubber gaskets act as a pump or diaphrsm of some sort to move fuel mixes thru and these rubber parts fatigue and need replaced...thus the rebuild kit...much of the time just a partial cleaning fails to solve the problem. Your compression numbers are good, so probably a fuel delivery problem. At least my two cents anyway....

 

[jimmbo]

When you put the carbs back on, did you make sure both are closed at Idle, and both open fully, and they are properly synced with the Spark Advance?