Rough running 90 hp two stroke

[Ian h.]

I have a 1987 yamaha 90 h.p. boat motor that has always run great until this spring. Every once in a while it will start to run rough at any speed and then smooth right out, some times you can go wide open and it runs fine then the next time before you get to full throttle it will start to hesitate and start ****ing. I changed spark plugs and it seemed to help for a short period then it started acting up again. I have fresh gas in it and this is very unusual for this motor to act like this. If you have any suggestions I would appreciate the help.
Thanks
Ian

[mitch]

have you changed the filters

[robert graham]

Check for bad fuel pump causing raw gas to get sucked into lower cylinder causing very rich mixture, wet spark plug, poor running. Pull that plug and check. Hope that's it, because it's a real easy, and cheap($50) fix for new pump.

[jonp]

It does sound like a fuel delivery issue... Like others suggested, check all of your fuel connections for leaks and replace the primer bulb if it is older. Robert suggests replacing the fuel pump, it is not an expensive part. Maybe $40 or 50 as Robert mentions...

I would also start running Seafoam or Cemtool thru the system to clean out the fuel system. You may have stuff in the carbs, old gas...ect. These additives will help with marginal clogs.. A high dose in few gallons would be a good plan, triple does in 3 gallons to start. Put the rest on your tank A can of seafoam treats about 20 gallons.

Good Luck