Bad Fuel Pump??

[77SceptreOB]

I'm in the process of restoring an older carbed outboard. It's a 1989 Yamaha V-6 Excel (225hp). Recently I had the 3 carbs rebuilt. Run very nice now.

EXCEPT, at about 4300 rpms and up, the engine seems to surge up and down about 200 rpms. It is almost like one of the three carbs is getting fuel starved. Bring the rpms back to 3500 and it's rock solid. Then take it up to 4600 rpms and the problem starts again.

But, if you hammer it, from say 1000 rpms it rockets up onto a plane (I run a 15" pitch alum prop) and runs solidly up to 5000 rpms or so. No problems and GREAT throttle response, no hesitation at all, just exactly what you would want. But after about 5 to 10 seconds at 5000 rpms the slight to moderate surging starts again.

Could this be that I'm not getting enough fuel to the engine / carbs. IE old weak fuel pump??

A couple of clarifications:

Carbs rebuilt by Yamaha Dealer last week.

Fresh, non-ethynol, gas run out of a new 6 gallon tank.

fuel line is 3/8"

Thoughts??