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post #1 of 72 (permalink) Old 09-02-2018, 05:18 PM Thread Starter
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Hello, and First Question

Hello,
I just purchased my first jet skis, a pair of 1999 GP1200s. I'd ridden a few times in the past and had owned a small ski boat in college, but this is new territory for me. They look to be well cared for and one of the skis is good to go, but the second has low compression in one cylinder. That'll be a winter project.

I was able to take the good one out this weekend, and it ran great. There are a few minor adjustments I'll want to make, but I'm really happy with the way it performed. My question though is, how long should I be able to run on a tank of gas. In two hours, I used about 3/4 of a tank. Is that normal? I expected better, but it was a lot of WOT. Like I mentioned, it seems to run like it should. Doesn't seem to be running rich. Let me know what you are getting.
Thanks!!

2x 1999 Yamaha GP1200 WaveRunners
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post #2 of 72 (permalink) Old 09-03-2018, 06:21 AM
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Pwc's, especially 2 stokes are not known for their mpg, but more for gpm.
The thing that should be looked at asap is the oil injection lines. They should be semi soft, but pliable. if they are not, they need to be replaced asap. when they get hard from age, they become brittle and will break or come off. It is a easy project, and takes very little time and money compared to trashing the engine. If they are still in good shape, I would at least put new zip ties on them.
I would also look at replacing the fuel lines, and rebuilding the carbs. No telling how long it's been since the last rebuild.
Compression should be about 120psi and plugs should be tan to med brown.
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post #3 of 72 (permalink) Old 09-03-2018, 07:02 AM
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+1 for what Rods already covered.
this is a non-power valve unit so you have no worries there.
your fuel consumption at that rate is normal.

Your fuel consumption rate at WOT is around 16/17 gallons per hour.

Last edited by Dave in DE; 09-03-2018 at 12:59 PM.
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post #4 of 72 (permalink) Old 09-03-2018, 08:21 PM Thread Starter
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Thanks for the input, fellas. I'll be giving both skis a good going over this winter in addition to rebuilding the one with the dead cylinder. From the reading I've done, I suspect an oil feed issue caused the compression problem, so I'll add your suggestions to my to do list.

On a related note, I had considered doing the oil feed block off and just running premix. If my gas mileage is going to stay this poor, I may have to rethink it. I can't carry that many gas cans with me everywhere I ride. Sounds like I'll need to stay close to a marina so I can refill.

Thanks again. I'm sure I'll be back with more questions.
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2x 1999 Yamaha GP1200 WaveRunners
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post #5 of 72 (permalink) Old 09-04-2018, 06:56 AM
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Nice ski's. Where in Missouri ?
I would leave the oil injection. They are very reliable systems. It's normally the oil lines that fail, and that's normally from age.
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post #6 of 72 (permalink) Old 09-04-2018, 07:06 AM
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Welcome to the forum, and I feel your pain. I have two '97 1100 triples, and if I would have ridden them for two hours at a time would have had the same result. Mostly WOT with me too, my wife, she gets much better mileage!

Mine were converted to the premix, and I just keep a couple of bottles that can mix with 5 gallons of gas at a time, so that I always have oil ready. I buy it by the gallon and pour into the bottles and reuse them.

Glad your one ski is running well. I also used to keep a set of plugs and wrench in my skis too, as inevitably, you are out on the water when it starts to run rough. That's why I'm selling those and bought a new 4 stroke, will get a second next year. The older skis are very stable, lots of fun, but she wanted something that didn't have to be messed with. Oh well, guess i'll be putting them on Craigs list tonight...

Have fun!
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post #7 of 72 (permalink) Old 09-04-2018, 07:10 AM
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Personally I'd leave the oil injection in tact. There a variable rate pump. At idle they mix about 200/1 up to 50/1 at wot. Saves oil and fouled plug when running no wake zones. If set and maintained they are pretty much bullet proof.
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post #8 of 72 (permalink) Old 09-04-2018, 07:16 AM Thread Starter
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Quote:
Originally Posted by rodsatheart View Post
Nice ski's. Where in Missouri ?
I would leave the oil injection. They are very reliable systems. It's normally the oil lines that fail, and that's normally from age.
Thanks, they look a little better in the pictures, but I think they've been maintained. Really clean inside and all the pivot points are greased, etc. I'm in Parkville, northwest corner of Kansas City.

2x 1999 Yamaha GP1200 WaveRunners
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post #9 of 72 (permalink) Old 09-04-2018, 07:30 AM
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Benn through KC a few times.
Also make sure you grease the driveshaft bearings.
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post #10 of 72 (permalink) Old 09-06-2018, 07:12 AM Thread Starter
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Second noob question. Can I run the engine for extended periods with the cooling system flush connected and water running through the engine? This would allow carb adjustments at home rather than at the lake.

2x 1999 Yamaha GP1200 WaveRunners
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