STX DI Runs Poorly when Hot... Ideas??? Help?!?!

[Kawi_Mon69]

My 2000 STX DI with 120 hours used to run great. I consistently got top end of 55 mph at ~6500 rpm out of her. Now, I'm only getting a top speed of 49-51 mph at 6200 rpm.

I could live with the 51 mph if it would last. However, after about 5 minutes of riding, the rpms drop to 5800 and top speed drops down to 35-39 mph. If I stop and let her sit for 20 minutes or so, rpms are back up and speed is up to 51 mph again. I think this is definitely a heat related issue.

There are no clogs in the cooling lines. Compression is equal at about 110 psi across all 3 cylinders. I recently rebuilt the jet pump, cleaned the injectors, replaced fuel filter, replaced the spark plugs (3rd set this season - she seems to foul them often), checked temp sensor, and checked throttle position sensor input and output voltage (at specs).

I'm not getting any warning indicators or lights, and the engine seems to be running fine, just slower. The engine does not seem to "miss" or stumble when this is happening.

I'm stumped. Does anyone have ANY ideas on what the problem might be?

Thanks,

[Wheels&Waves]

Re: STX DI Runs Poorly when Hot... Ideas??? Help?!?!

Looks like you have checked most of the things that you should. A couple of other things you might look at if you have not yet....
Check you charging system to make sure it is working properly. A drop in voltage may cause your symptoms. Also, try trimming your spark plug wire/boot connection.
Another possibility for the drop in power could be an exhaust leak into the hull. If you have exhaust gasses recirculating back into the intake, your engine will bog down and will cause plug fouling too.
I haven't had a lot of hands on with this model, but these are things I've seen with similar units.