Newbies ZXI 750 Boggs down? - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
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post #1 of 7 (permalink) Old 10-27-2007, 02:41 AM Thread Starter
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Unhappy Newbies ZXI 750 Boggs down?

I could use a little help!
I got a 97 Kaw zxi 750 twin carb. It fires up, idles, & revs up great out of water (running off the garden hose). Once I put it in the water every thing is a little more stubborn. It idles a little slower & rougher like a cold engine does, but its still going. After it warms up for a while, I get on the throttle hard & fast & it bogs down & stalls. It's a little stubborn to start after that but once it catches again its acts the same as earlier. If I feather the throttle a little it grabs & takes off like a bat out of hell. If I stay on the throttle its fine. Once I let it go it sounds like it wants to bogg down & stall again till I catch it with the throttle & keep it going. I called a couple of places one said the air/ fuel mix screws need to be played with. The other place said the acceleration pump is clogged. The guy I got it from said the carbs were recently rebuilt, He was thinking that it was a stater problem. I was playing with the air/ fuel mix screws but because itís not in the water with a load on it I canít tell if I made it better or worse. Can any one help me before I sink this thing for good? THANKS!!!!
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post #2 of 7 (permalink) Old 11-07-2007, 03:56 PM
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Wow, ok you sure didn't ask an easy question for your first one!!!

What you've described sounds like its being caused by an improper A/F mixture. Now as to why that mix is off is going to require some troubleshooting.

There are 3 basic areas that could be causing your issues:
1) You could have an air leak causing the engine to run lean, VERY BAD
2) Your reeds could be worn or bent and would cause hesitation and stumbling but hopefully no real damage.
3) Your mixture screws or carb could be improperly adjusted/tuned

Numbers 2 & are the easiest to test for and fix so lets start there.
-For #3, pull out the spark plugs and look at the electrode base. What color is it? Can you post a picture of it so the color is visible. If the mixture is correct then the base will be a chocolatey brown. I don't expect this since that would mean you shouldn't be have your problems.
-For #2, remove the air filter and while the engine is running or cranking put a rag or paper towel near the carbs throat. If the reeds are ok then there shouldn't be any flapping wich would indicate pressure venting back through the carbs.

If the plug colors are off, then adjust the carbs. Too dark and you should lean out the mixture, and too light would go the other way. If the reeds are damaged then you'll need to pull off the manifold and replace them.

If neither one of those fixes work then you'll need to start looking for an air leak into the engine. This isn't terribly hard, just time consuming since the best way is to remove the engine from the ski.

To test for an air leak you need to pressurize the engine once you've sealed off the intake and exhaust. The engine should hold 10psi with now more than a 1psi per minute loss. Anymore than that and you have a significant leak. To find a leak pour soapy water on the engine while its pressurized and bubbles will show where you need to fix.

Thats a basic run down of what you need to do... There is more info available but I don't want to type it unless you need it, so just ask...

"Build a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life!" - Anonymous
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post #3 of 7 (permalink) Old 06-27-2008, 01:32 PM
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I am having a similar issue with my 98 Kawasaki 1100 STX. I will try the suggestions you have given, but I had another question. I wanted to replace the fuel filter, and was wondering if you knew if I needed to use an OEM filter ($35), or is there a preferred after market filter that would be just a good and cheaper??

I am new to the JetSki game, and am wanting to learn as much as I can so I can keep it running myself without paying through the nose for maintenance!!!

Thanks in advance for your help...

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post #4 of 7 (permalink) Old 06-29-2008, 09:48 PM
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Hey, I got your PM but thought I'd answer it here so everyone can see...

You can obviously use the OEM filter, and that is the easiest option. However due to the cost of an OEM filter I usually put an inexpensive inline filter right before the carbs. The replacement elements are usually sold in packs of 3 for about $5 so they're pretty cheap, plus most are glass so you can see fuel flow and if its getting dirty! I've always used the ones you can find at places like Autozone because of availability but anything like that should work.

Let me know if you need more clarification on what I'm talking about, it's been a long day and I'm pretty sleepy so I might not be making the best of sense...

"Build a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life!" - Anonymous
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post #5 of 7 (permalink) Old 06-30-2008, 11:08 AM
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Thanks Knightofwyte!! Good advice!! I'll do just that! I am not a master mechanic obviously, but I couldn't see what could be so special about the OEM inline filter! I was hoping to find some more affordable filters like you mentioned, so I could replace them more often!! THanks again!
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post #6 of 7 (permalink) Old 07-06-2008, 11:35 PM
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I haven't had the issue since I sprayed down the carbs with carb cleaner, changed the fuel filter, ran 2 tanks (14gal I believe) of gas, each mixed with 2 cans of SeaFoam per tank. Currently I have the tank full and added one can of SeaFoam. I am hoping my carbs were just dirty causing the floats to stick or something starving it from fuel at high RPM. I have ran mine hard the last few times out without a problem...

I will report back if I ever have the problem and find the fix...
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post #7 of 7 (permalink) Old 07-02-2009, 06:34 PM
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This deservesa bump. I have had a few skis with this issue. Over and over this is the symptom. Runs fine out of water. Get it either to the water or "warmed up" and bog city, ddying with throttle application. UGGG!!!! Anyhow, on a few occasions it has been an easy fix of:
1) New spark plugs
2)replace fuel filter
3)carb cleaner
4) DEAD BATTERIES..ya. I know. Check stator..?
5) rebuild carbs ugggggg..

Anyhow there's my 2 cents and bump!

I'd love to see more input on this issue as it is obviously a common problem.
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