1998 Speedster low thrust and rpm

[hazzo]

I have had some problem with the port engine for a while. It starts up ok and runs fairly smooth on idle, but when increasing the throttle it starts to run really bad, sputtering and not coming up to more than approx 3000 rpm. The colder the engine is the better it runs and the more rpm it gives. When getting warmed up, the max rpm drop to around 2500.

Cleaned the carbs and checked everything, but the problem still exists.

Anyone with an idea?

 

[Sandman251]

First thing... check the compression. Second thing... check the compression. Its very easy to do with the info on this site. Check back when you have the numbers.

 

[hazzo]

I checked the compression and it's between 9.7 and 9.8 bar on all cylinders.
I have checked and cleaned the carbs, checked the ignition system and now I'm leaning towards an issue with the MPEM or maybe that the port engine doesn't recieve a signal that it's in the water and reduces the max rpm.
I read somewhere that the rpm will be reduced on land but haven't found out how this is done. Any help on that?
If it's the MPEM, is the only solution to replace it?

 

[Mustainefan]

Think I may be having the same issue on my starboard engine. I have a 97 speedster and ever since I owned it the starboard engine was always a little behind the port engine in rpms (mostly at higher speeds), and I’d usually up throttle it a little to keep them in sync. But within last few weeks I’ve noticed this getting a little worse at times.

Last few times on the water it will basically be fine for 15-20 min and then it goes lame so that the rpms can’t go over 4000. I‘ve also noticed that it can recover out of nowhere for a little bit, but it is hardly reliable.

When I first had the problem I thought it might be the sparkplugs, so I changed them both. It seemed to work, but after a few more times on the water it’s still doing it.

I’m NOT an engine guy, but I’d like to figure this out on my own. If anyone has successfully solved this problem I would be most interested in the details!