GregP

Twice now I've had the port motor change RPM at fixed throttle and max RPM at full throttle after landing from crossing a big cruiser wake. First time the RPM went down about 400, yesterday it went up about 400 (and water pressure dropped for a few seconds). I've looked for loose wires and can't find any, and I can't wiggle them while its running under load to see if one is broken. The RPM change is instant, feels like ignition advance going in and out??

I never found anything "wrong" the first time when the RPM went down, but after fiddling a while (synced all the carbs and replaced the TPS sensors) it went back to matching the stbd motor RPM until after the cruiser crossing yesterday when it suddently went up higher than the stbd motor.

I changed the TPS sensors on both motors as they tested out of spec and the manual says they are a common cause of timing variation. The other sensors (crank position and knock) are I think solid state, so shouldn't be affected by a good jolt?

I'd just finished making 6 passes up and down the river, constant throttle and trim, and they held RPM within 100 and both throttles were even. Then after the crusing crossing the port motor started running 400-500 RPM "higher" at the same stick position.

I'm discounting fuel since the power went up ??

Any ideas where to look next or how to test it? Do I need to hire a cruiser to go out with me so I can keep crossing his wake to track it down? Anyone in Annapolis want to lend a second set of eyes (and brain)?

Motors are 1993 Yamaha 250 carbed.

-Greg