!984 Yamaha 90 bogs at high rpms

[amityray]

I have a 1984 Yamaha 90 that starts and idles great. But after a few minutes of running at high rpms the motor falls flat and almost stalls. After a few minutes at idle it will run up and do the same thing. Has anyone else had this problem? I've checked all the fuel lines and filter, looked for loose connections but nothing obvious is wrong I also tried a fresh tank of gas but nothing seems to help. At the beginning of the season it was ok but it slowley started getting worse.

[johnnyracer]

its screaming fuel . tank pick up. primer bulb motor side restriction ?

[martinc]

Short the pink to black at the thermo switch on the cylinder head to make sure the alert horn work's properly. Thank's Martin

[Superbender]

Ray put a vacuum gauge on the fuel line just before filter on motor.

[Ray Neudecker]

Two possibilities are overheating and the intermittent fire from the CDI. Shorting the pink wire going to the thermo sensor will let you know the horn is or is not good.
Intermitent firing problems have sometimes been a problem with the 3 cylinder Yamaha's. Use of a timing light will it is in shutdown will help trouble shoot that.
Johnny Racer is also correct that it could be a carb problem or fuel restriction even though they are not often intermitent.