90hp Force Mercury SportJet

Im in the right forum! But after searching around for threads on the subject I can't find anything exactly like mine. So here goes...

I just got a jetboat for a good price+trailer. But its not starting. Seller told me he started and ran around back in September and since he just let it sit.

Motor is in a Regal Jetboat '94. It spins fine when the spark plugs removed. With the spark plugs on, its getting jammed at certain spot and wont crank. I dont know what is causing the problem. So I took all the spark plugs off and did a compression test. Cyl 1(bottom) 20psi, Cyl2(middle) 54psi, Cyl3 (top) 40psi

I know its not right with compressions that low. I haven't been able to do the spark test because I misplaced the spark tester somewhere.

So im hoping that its not causing by something which requires a complete rebuild.

Re: 90hp Force Mercury SportJet

The compression readings are WAY low.Spray some WD or any light oil in the cylinders.
Do the test again.
Check the battery for a complete charge.The starter,if original might need service.
I wouldn't worry about the spark until you get the right comp readings.
Get a different guage.I think Auto Zone loans tools.
Fill out the profile,you might be close to someone who can help.J

Re: 90hp Force Mercury SportJet

Thanks for the reply Jerryjerry. I thought that was too low as well. It turned out, the stator and the loose magnets were coming in contact with each other while cranking. SO that what causing it to stuck at certain points. I gotta wait a few days for the flywheel removal tool and possibly replace the stator and a few magnets. Good thing I have a broken 120hp, I will swap out the parts and hope that would be it.

The boat engine is pretty much pristine. Im not an expert but from observing the bottom of the boat, I found almost none but one nicked. So I am pretty sure it was just laying at the dock getting the nasty tan which ruined all the upholstery.

Will update after the holidays are over. By then I should be able to get it back running.

Re: 90hp Force Mercury SportJet

Make sure the ignitions are the same of the flywheel wont work, as a CDM flywheel wont fire a ADI igintion

Re: 90hp Force Mercury SportJet

Got the flywheel but it didnt fit 'cuz its from a 96 engine. The crankshaft diameter was way bigger. But I picked up a used on on Ebay. But its hasnt been started in months. How long does it take to start it ?

I started it and seems like its spinning then slowing down then going again.. like the up/downs pistons/compression slowed it down but no spark