merc 35, 1985 od18

[Brent]

Hello all,
I have a 1985 merc 35 that used to run well. It topped out at 22 mph (gps) For a while the top speed was getting slower and slower, down to 15 mph. Now it runs well at very slow speeds ( 5 mph) and very choppy at anything higher. With no load the engine revs up nicely and goes to full power, with the prop engaged things are not good. It burps a lot and sputters. ( am I being too technical?)
I changed props to a smaller one and gained a few rpms but nothing significant. Also the hull is clean and the boat is not overloaded.
Any ideas? Is a carb rebuild owner maintenance? I have been using staybil.
I don't like not trusting the motor.
Thanks,

[JIM M]

Check the fuel filter and the compression. Have you changed,checked the spark plugs recently ?
good luck

Jim

[Brent]

Thanks, I did replace the fuel filter and the plugs but did not do a compression test. Good idea, I will do that.

[Tberks]

Your carbs may be gummed up...