80 Pounds on one and 120-130 pounds on the other after unlocking engine - Seadoo Forums
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  1. ☑ ORIGINAL POSTER #1
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    Default 80 Pounds on one and 120-130 pounds on the other after unlocking engine

    I have taken the head off and cleaned the cylinders, and the bad one which is the one closest to the front had some rust in the cylinder. I can get the ski to fire with starting fluid, but I have bad gas and haven't cleaned the carbs yet. My question is, If I clean carbs and get this ski to crank up, will it run half way decent at this compression, or am I totally wasting my time. Will I at least be able to make it thru one summer if I baby the thing. Also, can any one tell me a ball park price of doing a top end job on this ski if I were to try to tackle it myself. Parts? What would a dealer charge. I assume I would have to hone the cylinder and put rings and pistons or just rings. Can you just do the cylinder with the bad compression?

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  3. #2
    seadoosnipe's Avatar
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    Default Another 10-gazillion answer!

    It's been written in this forum 10-gazillion times, NEVER USE STARTING FLUID. There are no lubricating properties in it and just to use it once can cause major damage to bearings, cylinder walls and rings.
    If your mechanically inclined, you may be able to do this work yourself. It's not rocket science. Your compression says your MAG piston is shot. You can become a member to get a manual and an un-limited supply of help here.
    For your parts, go to www.sbtontheweb.com and use there parts lookup tool on the left hand side of the page. You can just purchase all the parts you need to redo the upper end. Better than taking to a machine shop for boring and honing, then buying new pistons........cheaper, I'm sure.
    Good luck..........and quite using starter fluid. If you need to spray something to prime for ignition, use WD-40. They use WD in the Diesel industry to start all their huge diesel tractors etc... in the winter months because not only is it flammable, it's got a lubricant in it..........
    Looking for tips and advice, researched articles on carbs, spark plugs and general maintenance can be found at Snipes Korner. You can also follow me on "Twitter".

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    Ever wonder what the inside of your 787cc engine looks like. Want to identify the parts, check out my thread on the 787. I'm sure there is something for everyone who want to learn about the internal parts.

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  4. ☑ ORIGINAL POSTER #3
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    Default Can I just fix the mag piston, or should I do both and

    when you say "shot" , does that mean it will not run or ever get any better. I want to try to run the ski. Will it run like this, and if so, how good. What is the minimum compression that you can run on and still have fun.

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  5. #4
    seadoosnipe's Avatar
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    Default Engine is bad...

    No, there is probably nothing you can do to make your engine run better. If both cylinders were 80, then, although that is below the minimum standard for the engine, it'd run smoother, but with a horrible reduction in horsepower.
    Here's the idea to try and help you see how compression works. First, when the fuel is induced into the cylinder, the compression stroke takes place, compressing the fuel/air mixture to pressures close to 150 psi. When ignition happens (spark from the plug), the resulting explosion is what pushes that piston down with maximum force to create the best horepower. The speed at which this takes place is 1500 times per minute at idle. So if you have one cylinder that pumps up to 80, then the next to 120, the forces of work are not equal. This is considered, "off balanced". It will create different pressures on your bearings and shaft at each revolution.
    Like the spin cycle of a washing machine off balance. It wobbles. Well, with compression seperated that bad, the crank is trying to wobble.
    That's about the best I can do in describing it.............Look for replacing the entire motor or doing an upper end job...........

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