98 Seadoo Sportster 717- can’t get up on plane

[Buggywhips]

Hello everyone, new to forum. Great info here and I hope to help people with what I can also.
My issue- I’ve rebuilt the carb, then changed out entire carb, carbon seal, jet pump and impeller and wear ring, checked compression which is 130/150. Replaces lines, adjusted throttle and tried to set high speed low speed. Plugs are dry after running and look to be running very hot.
I put new plugs in - was able to get up on plane and in ran good for about 5 minutes before fouling plugs and losing power. I put in new plugs again and the same thing occurred.

I am at a total loss on what the issue is and would appreciate any guidance or tips.

 

[Sandman251]

It would be very helpful if you could describe in great detail what you mean by "can’t get up on plane". What EXACTLY happens when you advance the throttle? Do the RPM's redline or do you sort of plow water @ 4K rpms? What sort of load are you carrying? Fuel, Gear, Passengers? What is the state of your battery? Age/charge?
We can talk about your compression #'s later. Thx.

 

[mikidymac]

If your compression numbers are correct your engine has a large mechanical issue as the numbers should never be that far apart.

 

[Buggywhips]

It would be very helpful if you could describe in great detail what you mean by "can’t get up on plane". What EXACTLY happens when you advance the throttle? Do the RPM's redline or do you sort of plow water @ 4K rpms? What sort of load are you carrying? Fuel, Gear, Passengers? What is the state of your battery? Age/charge?
We can talk about your compression #'s later. Thx.

Thank u for the reply !! Ok, So when I advance the throttle, I can get to mid throttle and it bogs and sputters a bit - but past mid throttle it will rev up nicely but not high revs- possibly around 4000k and it will not push the boat up and out of the water enough to get on plane. No redline, no rev limiter. I’m one person testing the boat and no gear and no other load. Boat is dry. Battery is a year old as far as I know. It takes and retains a charge without any issue so far as I can tell.
Plugs seem to be running too hot and although they’re not white, they are very dry and look to be fouling from possibly oil or heat. I’m just not sure. I just know that after I change them, the boat runs very well without issue for approx 5-8 minutes and then loses power.

 

[Sandman251]

Next time out pull the choke while you're trying to get on plane. Observe whether the boat chokes out or surges. It certainly sounds like you are running lean. If the plugs are dry, they aren't fouling from a rich condition. You want to run the boat as little as possible until you find your problem to avoid any (further) major engine damage. Like Mikidymac said above, those compression numbers are suspicious. Check for anything that could obstruct free-flow of fuel. Lines, connections, filters, vents selector switch, etc. If everything is in order, I'd be looking at your carb again. I had a problem very similar to yours once on a challenger 787 single that ended up being a bad rectifier/battery, but I wasn't running lean.

 

[Buggywhips]

Sorry for delay. I couldn’t get on to the forum !
So I actually ended up having to pull the motor and found a bent piston rod..... looks like I’m deeper in than I thought !!!!