John Stardust
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Water intake ball valve?
- Thread starter John Stardust
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artr
Well-Known Member
I've always checked mine with the ski on a trailer out of the water. But it really shouldn't make a difference, the compression reading should be the same. You should hold the throttle open while you're cranking the engine to take the reading and connect the plug wires to the shorting block.
John Stardust
Member
Thank you
AKnarrowback
Well-Known Member
It should not make a difference of in or out, just if you prefer standing in the water when you work. (Joke)
Seriously.
Check it out of the water, with a cold motor, have a good charge on the battery to crank the motor fast, hold the throttle wide open when cranking and you should only need to crank it for a second or two at the most.
Make sure you are using a good compression tester. If you know of someone with a snap-on, Mac or a higher quality tester that spins into the plug hole. Watch the gauge as you crank the motor over, it should jump up to the true compression in a second or two, when the needle stops climbing you are there. Check it with "dry" cylinders as I call it, no extra oil dropped or fuel dropped in the plug hole to cheat and get higher numbers. Just crank on it as it would be in an everyday situation with the carbs and oil injection adding only what they would under a normal start.
You are looking for close to 150psi or a little lower. Some people go by the 10% rule for a max difference between the two cylinders, if I see 10psi or more between my cylinders I'm going into the motor, if I'm within 5 I'll call it good enough but watch it. If you are around 120psi then you are looking at low enough compression to cause problems in performance. This doesn't mean you can't ride it if you can get it started, but it indicates things are worn and need to be put on the "to do list soon". The low compression could be related to scoring of the piston and cylinder and it's just not a good idea to run rough surfaces on each other, fix it asap. I only know of one sea-doo that literally wore out the cylinders without any scoring or damage, but it had 50ish gallons a weekend go through it for years.
You are right about the water in the exhaust system. If water us present the motor has to push it out to run and starting a motor can be a fight. With DOOs just spinning the impeller in the water can fight a low compression motor to start.
I have a 94 XP that I modified the pump nozzle, trim ring so I can stand the machine on end with ease. I can stall my motor out 100% of the time if I stand it on end, hit the throttle to rocket the machine straight up then let it fall back shoving the exhaust outlet deep under water while letting the engine drop to an idle. The exhaust can't fight the water pressure 3 feet down and it kills the motor every time.
Seriously.
Check it out of the water, with a cold motor, have a good charge on the battery to crank the motor fast, hold the throttle wide open when cranking and you should only need to crank it for a second or two at the most.
Make sure you are using a good compression tester. If you know of someone with a snap-on, Mac or a higher quality tester that spins into the plug hole. Watch the gauge as you crank the motor over, it should jump up to the true compression in a second or two, when the needle stops climbing you are there. Check it with "dry" cylinders as I call it, no extra oil dropped or fuel dropped in the plug hole to cheat and get higher numbers. Just crank on it as it would be in an everyday situation with the carbs and oil injection adding only what they would under a normal start.
You are looking for close to 150psi or a little lower. Some people go by the 10% rule for a max difference between the two cylinders, if I see 10psi or more between my cylinders I'm going into the motor, if I'm within 5 I'll call it good enough but watch it. If you are around 120psi then you are looking at low enough compression to cause problems in performance. This doesn't mean you can't ride it if you can get it started, but it indicates things are worn and need to be put on the "to do list soon". The low compression could be related to scoring of the piston and cylinder and it's just not a good idea to run rough surfaces on each other, fix it asap. I only know of one sea-doo that literally wore out the cylinders without any scoring or damage, but it had 50ish gallons a weekend go through it for years.
You are right about the water in the exhaust system. If water us present the motor has to push it out to run and starting a motor can be a fight. With DOOs just spinning the impeller in the water can fight a low compression motor to start.
I have a 94 XP that I modified the pump nozzle, trim ring so I can stand the machine on end with ease. I can stall my motor out 100% of the time if I stand it on end, hit the throttle to rocket the machine straight up then let it fall back shoving the exhaust outlet deep under water while letting the engine drop to an idle. The exhaust can't fight the water pressure 3 feet down and it kills the motor every time.
AKnarrowback
Well-Known Member
Which model is it, what engine type is in the machine?
John Stardust
Member
97 gti 717
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