Yamaha, 4-stroke Mid Range Power loss

[frustratedboater]

I have a friends 02' Yamaha 25hp 4-stroke Jet Drive, that suffers from mid-throttle power loss. I had rebuilt the carbs which were fairly dirty. I was very meticulous in the cleaning and blew out all the passages. The gaskets were in great shape and not flattened and re-used them. He said a 'dealer' serviced it.
I then checked valve lash and re-set to spec (some were out). I had ran it quite a while attached to the hose and throttled up nice.. I checked the vacuum on each and #3 was pulling more and synced them true.

He took it out and stated: Idle was okay as well as high speed, but the mid-range kind of fluttered. Other than taking another look at the carbs for dirt in the small jet, not sure what else it could be.

 

[frustratedboater]

I have a friends 02' Yamaha 25hp 4-stroke Jet Drive, that suffers from mid-throttle power loss. I had rebuilt the carbs which were fairly dirty. I was very meticulous in the cleaning and blew out all the passages. The gaskets were in great shape and not flattened and re-used them. He said a 'dealer' serviced it.
I then checked valve lash and re-set to spec (some were out). I had ran it quite a while attached to the hose and throttled up nice.. I checked the vacuum on each and #3 was pulling more and synced them true.

He took it out and stated: Idle was okay as well as high speed, but the mid-range kind of fluttered. Other than taking another look at the carbs for dirt in the small jet, not sure what else it could be.

Any ideas..

 

[99yam40]

timing light will tell if timing is in spec and advancing as it should
and it will show if spark is good when problem shows up.

could be off idle ports are dirty, so has a hard time transitioning to upper RPM.
heated sonic bath cleaner may be a good idea

 

[frustratedboater]

timing light will tell if timing is in spec and advancing as it should
and it will show if spark is good when problem shows up.

could be off idle ports are dirty, so has a hard time transitioning to upper RPM.
heated sonic bath cleaner may be a good idea

I appreciate the direction to look. I haven't thought about timing.. will take a peek at that. I thought I cleaned everything pretty throughly and flushed the lines, but I'll just have to bench it again. Thx