91 Yamaha 225 runs erratically a @ high RPM

[Zap-Man]

Hello,

I recently bought a Mako 230 Walk Around with a 1991 Yamaha 225. The boat and motor had been sitting for perhaps 8 years. I had a competent marine mechanic go over the engine, he rebuilt the carbs, put in new fuel pumps and said the compression was good in all cylinders. She runs fine at low RPM's, but won't go over about 36-37k RPM at speed, and sort of "pulses" up and down in rev's running flat out. Fuel is clean, have checked for water, drained carbs, inspected main jets, all seems fine.

Any ideas?

Thanks!

 

[JUSTINTIME]

Re: 91 Yamaha 225 runs erratically a @ high RPM

fuel pressure/vacuum test is in order
any alarms?

 

[Zap-Man]

Re: 91 Yamaha 225 runs erratically a @ high RPM

No alarms. Totally cleaned and checked out the recently rebuilt carbs, tried running it on an alternate fuel source as well. Discovered that new fuel pumps had been installed without gaskets on engine side. Hoped that was the cause, with lack of vacuum pressure, but no. Pumping the bulb has an effect of performance, so I still believe it's fuel supply related. Totally baffled & frustrated at this point.