Twin Rotax 717's: One engine sounds slow

[splishy]

Hey everyone, I'm trying to figure out if there's an issue and what I can do to diagnose it if so. I recently got a 2000 Challenger with twin 717's and it feels and sounds like the left engine may be underperforming a bit. The left tach doesn't work so I'm going to swap the right and left ones before my next time out to get a better idea what's going on with the left engine, but my right engine is going at ~7500 rpm at WOT.

With 2 people I get up to ~35mph @ WOT, 3 people is 20mph, and 4 people is around 13-15mph. Regardless how many people I have, it seems like getting to plane and then finally be up to speed takes a while (maybe 15-60 seconds depending on # of people). Are these normal or unusual top speeds?

The right engine SC feels like it's kicking in around 5.5k rpm (around 75-80% throttle) and then spikes quickly up to 7k, whereas the left engine doesn't ever get that feel or sound even at WOT. It also feels like the boat is pulling to the left a little and I'm always having to counter steer to the right a little bit.

The left engine sometimes dies when throttling from idle as well (maybe 2-3 times in a day on the lake) whereas the right one never has that issue. It also feels like it takes a little longer to start (maybe 3-5 seconds longer than the right).

Any ideas or suggestions would be great, thanks!

 

[POPPS]

Do a compression test to start,,, it could easily be a “ failing” motor.
Check that it is charging,,, a failing regulator could cause your symptom,
The boat is “steering” because your other strong motor is pushing the boat to the weak motor side.
If you are lucky, it could just be the carbs.

 

[splishy]

I did a compression test on the left engine and one of the cylinders is about 90 and the other is right at 120.

Here are a few more observations I made from the latest lake trip (all about left engine):

• Doesn't start easily or will sometimes die shortly after starting (first time that day)
• Starts easily after the first time it's been run for 10ish minutes
• Only hits about 3k rpm at WOT until it's been running for 5-10min, then spikes up to 7.5k rpm
• During 3k WOT period, a grip of white smoke comes out of the exhaust at any speed and engine feels boggy
• After 7.5k WOT is achieved, no more smoke from exhaust at any speed and engine responds very well
• If the engine is off for a short while (maybe 10+ minutes?) then it goes back to the 3k WOT phase, 5-10min of running to 7.5k WOT phase
• It feels like the boat in general is going through a lot of oil (I've already had to put >1gal in after ~30gal of gas)

Part of me is thinking this could just be a piston ring and a top end rebuild would solve the problem, because it totally sounds like an oil leak to me. But I'd love to get the expert's thoughts on here since I'm new to 2 strokes and more familiar with car engines Is it worth rebuilding/saving or just swap for a fully rebuilt engine at this point?

Thanks!

Edit: my right engine also is doing something interesting. At about 1/2 to 2/3 WOT it'll hit about 5k rpm and then spike to 7k rpm after a few seconds. It his 7.5k rpm at WOT and barely pushes the boat forward if the left engine is in its 3k WOT phase (10-15mph for a few minutes until planing then hits 30mph). This last run, the right engine would be at 7.5k WOT and then randomly drop to 4-5k WOT, then back to 7.5k, etc (fluctuating rpm). It didn't do that on previous runs.