Help diagnose my engine not running at full capicity

[Robert Frost]

I have a 2001 LS2000 jet boat with twin 1200 2 stroke engines. One engine runes fine out of the water but when in the water, it only goes to about 4000 RPMs and than will shut down. I replaced the spark plugs, CDI and the stater but I still have the same problem, The compression is all three cylinders is at 115 to 120 psi. I have changed the fuel filter. The other engine works fine. Does anyone know what I might do? Thanks. Robert in Arizona

 

[swatski]

Robert -
Welcome to the club.

I can not offer any sound advice myslef as it's been too long since I messed with my last 2-strokers (love them!) but you have come to the right place!

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[itsdgm]

Welcome @Robert Frost. It's been several years since I've worked on a 2 stroke boat. Mine was a sea Doo. It's really tough to diagnose without more history. How long have you owned the boat, when did this problem start, etc. Often times what you're describing is a fuel delivery problem. When was the last time that you've rebuilt the fuel pumps, or cleaned out the jets?

Anyway, welcome to the site and good luck with figuring it out. I'm sure there's other guys with better tips and tricks that will chime in soon.

 

[bronze_10]

i had an old jet ski years ago that was two stroke... it seemed I was rebuilding the carbs all the time to keep it running right. Maybe look at that.. also I found a fuel line that was so old it was collapsing when you hit the gas restricting flow. I also had problems with the part that supplies the spark to the plugs.. on a car it would be the distributor but i can t remember what it was called on that old ski. It was bad and the ski ran great on land.. but in the water after about 10 min it would go to half power and the motor would kinda lope. One that motor, a seadoo brp 686 i think, both plugs fire at the same time. The one that was in compression would combust the other was in exhaust and did nothing from the spark. On mine once it got hot one spark would not reach the plug. I replaced the part and it ran fine. NO CLUE if any of this helps. And this is the extent of my marine 2 stroke knowledge. Good Luck and welcome to the site.!!!

 

[4x15mph]

See my response in your other post