'99 GP800 issue after carb and cylinder rebuild - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
 
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post #1 of 7 (permalink) Old 05-24-2019, 07:11 AM Thread Starter
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'99 GP800 issue after carb and cylinder rebuild

1999 GP800 in good condition. Bought it last fall, had new power valves and Waveater clips installed, new pistons installed and the carb was rebuilt. New fuel, new fuel selector knob (on, off, res), new fuel filter. I use pre-mix.

I ran the ski today. Started right up, but there is a problem. Moves fine at low rpms, but tops out at 4500 rpm. I spent 45 mins or so driving around the harbor. If I had enough room and held the throttle at a half twist, I could get up to 20 mph and then it would gradually gain speed. Periodically, it would launch into full throttle mode, but the water was choppy and I couldn't hold this for long. Meanwhile when the ski is maxing out at 4500 rpm, there is constant surging of the engine, as if it's getting spurts of fuel. When on the trailer, the engine runs properly, with no maxing at 4500, so the problem seems to be under load.

The reeds were not inspected or replaced during the engine work at the dealer. The service guy tells me the reeds are not likely to be the culprits here. He thinks maybe the problem is with the impeller, maybe too much gap between the impeller and the sealer ring. I bought a feeler gauge and will inspect this in a couple of days.

Any thoughts or suggestions?
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post #2 of 7 (permalink) Old 05-24-2019, 09:26 AM
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Surging is a fuel issue. Normally a lean issue.
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post #3 of 7 (permalink) Old 05-24-2019, 12:52 PM
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Only other thought Is power valves not opening. As they open around 4500/5500 rpm range. There easy enough to check though. Remove the seat watch the valve cam on left rear of motor while you start stop motor. The valve cam should rotate 1/4 turn cc then back. Valve cam is the BLK 2" diameter disc with 2 cables attached. If they work, then try starting and rev up to see if they open at speed.
The power valves must work to get to the upper rpm range.
But as Rods stated the stutter sounds more like fuel issue. I only bring up the valves as they open around the rpm you state is not going above.
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post #4 of 7 (permalink) Old 05-26-2019, 06:25 AM
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To expand on this a bit, excess clearance between the impeller and wear ring will cause a slipping effect (high rpm and no or limited movement). Have you pulled the plugs to see what they look like ?
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post #5 of 7 (permalink) Old 05-26-2019, 12:13 PM Thread Starter
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I have not pulled the plugs, which were new before my 45 minute test ride. I can do so today or tomorrow. I want to start it on the trailer and see what happens to the rpms when the motor is not under load. If the rpms go up smoothly past 4500 to the higher range every time I pull the throttle, that means the problem is only occurring under load. When I'm doing this I will also see what is happening with the power valves.

If this is a lean issue, where would the problem be? The carbs were completely rebuilt by the dealer, but they didn't touch the reeds. Is this where the problem could lie?

Finally, I bought a feeler gauge and will try to ascertain if there is an issue with the gap around the impeller. I understand that too much clearance should not affect engine speed, only speed on the water. Or is there any way an impeller problem could somehow limit rpms?

Thank you Dave and Rods.
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post #6 of 7 (permalink) Old 05-26-2019, 03:26 PM Thread Starter
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OP here with an update. Ran the ski on the trailer. Strong cooling water flow from the port on the front left side--first time I've seen water come out and the water stayed cool to the touch. Valve cam does engage around 4500 rpm, moves about 1/8 of a turn, then turns back when the throttle is released. RPMs move from 1000 at idle smoothly to a max of around 7500 at WOT. No hesitation and no 'surging' sound. So this problem is only happening under load on the water. Took off the impeller intake grate and the impeller looks OK--dings, but the clearance does not seem to be excessive. So where does this leave me? I'll take it to be fixed if I can tell them where I think the problem is. Thanks all. I can share a short video by PM.
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post #7 of 7 (permalink) Old 05-26-2019, 06:37 PM
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Originally Posted by Peebs View Post
OP here with an update. Ran the ski on the trailer. Strong cooling water flow from the port on the front left side--first time I've seen water come out and the water stayed cool to the touch. Valve cam does engage around 4500 rpm, moves about 1/8 of a turn, then turns back when the throttle is released. RPMs move from 1000 at idle smoothly to a max of around 7500 at WOT. No hesitation and no 'surging' sound. So this problem is only happening under load on the water. Took off the impeller intake grate and the impeller looks OK--dings, but the clearance does not seem to be excessive. So where does this leave me? I'll take it to be fixed if I can tell them where I think the problem is. Thanks all. I can share a short video by PM.
Ok. As you stated this is an under load issue. The impeller would only limit ski speed, rpm should still Max out and hit limiter. Almost has to be carb issue in my mind. Have you pulled plugs to see what they look like. Lean/rich.
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