Scarab 255 w/twin Rotax 300s RPMs

[Gwaters20]

Took my boat out for a little cruise this weekend. First leg of the trip both engines ran fine and close RPMs at all speed ranges. When we went to head back in after being anchored out for an hour or two, the starboard engine starting running almost 2500 rpm slower than the port engine at about 35 mph. They idled at the same speed and the RPM difference seemed to increased exponentially with more throttle. What’s going on?

Engines have 30 hrs and diagnostics were just ran before we bought it. No codes or lights.

 

[Luc Lafreniere]

I'm not an expert on twin engines at all. But I'd definitely check and possibly replace spark plugs on the slower engine. The symptoms point to this and it's an easy thing to try.

 

[Sidarousmg]

another possibility: the engine running lower RPMs is actually running correctly, while the other motor is running excessive rpms because of cavitation. you may have something stuck in that pump.

 

[Gwaters20]

another possibility: the engine running lower RPMs is actually running correctly, while the other motor is running excessive rpms because of cavitation. you may have something stuck in that pump.

I haven’t had time to disassemble the pump, but I did snake a good camera in both of them and I didn’t see anything or any defects in the impellers.

 

[Gwaters20]

I'm not an expert on twin engines at all. But I'd definitely check and possibly replace spark plugs on the slower engine. The symptoms point to this and it's an easy thing to try.

I will have to check into this!