2000 Yamaha 60hp engine oscillates

[craker]

I just repowered my 17' Swan Point skiff with a 2000 60 hp Yamaha. It has only about 30 hrs total on the engine. The seller said he had the carb rebuilt prior to selling. I have had it out 4 or 5 times since I repowered it. The last couple of times out, the motor starts to loses power while on plane. It will either drop several hundred rpms over a few seconds or it oscillates like it is dropping a cylinder and then picking it back up. I changed the plugs, NGK's. The motor also has gotten a deeper, Throatier sound at full power than it did at first.

This motor looks like brand new. Any ideas about what is causing the lack of power will be greatly appreciated.

 

[99yam40]

Re: 2000 Yamaha 60hp engine oscillates

check compression, spark, and timing.
Check fuel pressure/vacuum.
If all is good the you are back to carbs is my thoughts

 

[AURanger07]

Re: 2000 Yamaha 60hp engine oscillates

Sounds kinda like the problem i was having with my 07 150 vmax. It is starving for fuel(one of my fuel pumps went out). I would check the fuel pressure like mentioned above. If the motor sat for a while, you might have a problem with ethanol in one of the lines. It will feel like a very hard spot in the line where it has created the blockage.