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  1. #1

    Unhappy Fixing up a free '95 SL 750

    Hi all. This is my second project PWC. My first was a '93 SL 650. My father owns a dealership and sometimes he's given a broken PWC when the repair bill is more than it's worth. 4 of them were decaying in a open lot when I asked if I could try and get one running. He said sure and I started on the '93 650 because it was the nicest looking and there was another 650 for parts. The bearing had locked on it and I rebuilt the engine with a new crankcase. It was a wonderful day to take it out for a ride for the first time.

    Now, I am on to my second. It is a '95 SL 750. A little weather checked. I will probably use the seat of the parts 650 as this one leaves pink everywhere you touch. The pump is missing but I was thinking the one from the 650 might work with the right impeller. The electrical box was a mess but I got it back together with an extra CDI that my dad thought belonged to it at one time. Went through the carbs and cleaned them. I was able to start the PWC and it idles on all three nice. But this is where I need help. When I give it gas it bogs and wants to die. Sometimes backfiring. The plugs are wet when I take them out. I set all of the needles to factory. My dad thinks it is an electrical problem...I don't know where to start so any help would be huge. I am including a little video of it running so you all can get a better idea.


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  2. #2
    Home grown engineer, and professional tinkerer. 2 Strokin' Polaris's Avatar
    Join Date
    Apr 2009
    Spring, Texas
    When you cleaned the carbs, did you make sure the jets were open. It really sounds like the high speed jets are gummed up, or that the fuel pump may not be delivering enough fuel to keep up with demand. The 750 in my signature had sat for a decade with a holed cylinder and pretty much the whole fuel system had to be addressed from the broken pickup siphons in the tank to the filters, jets, and check valves in the carbs. John Zigler was able to ship rebuild kits to me, and after the kits I have put about 5 hours on the machine with good luck so far (exempting a thru hull fitting leak).

  3. #3
    When I remove the plugs they are really wet, so I don't think it is running out of gas. Correct me if I'm wrong, but I don't think that would cause the backfire.

  4. #4
    Home grown engineer, and professional tinkerer. 2 Strokin' Polaris's Avatar
    Join Date
    Apr 2009
    Spring, Texas
    If you are positive the fuel system is working properly, you might make sure the plugs are getting proper spark. If not, you might snip the spark plug wires back 1/4" and see if that cures the problem. Otherwise, it could be a coil(s) going south (if the electrical box was flooded or rusty) or a magneto/stator on the way south. I would recommend checking K447's signature links for the diagnostics on the electrical parts. They have been most helpful to me for more than one application. You will find links to manual's that will give ohm readings you can compare with for each of the diagnostic tests. Keep us informed on your progress.

  5. #5
    So, I found another symptom. There is a lot of oil coming out of the exhaust. The water baffel was full of black oil. I think that is what was backfiring. Could the oil pump be bad and oil fouling the fuel when I try and increase the RPMs??? Any ideas on how to test this theory?

  6. #6
    Talked to my dad. He says that black oil oil is probably just leftover gas and oil from the engine not igniting and sending it through. Says it is probably what was causing the backfire though. Once again, back to the ignition system.

  7. #7
    seaobin's Avatar
    Join Date
    Jun 2007
    Raleigh, North Carolina, United States
    Backfire is caused by a open exhaust port during ignition. check your crank phase and timing

  8. #8
    I am borrowing a timing light. I found the timing hole on the engine but it is out of the way. I can't see straight down the hole. Is there a trick or do I have to rig up a mirror of some sort. Thanks for any help.

  9. #9
    Canadian Beaver Inspector jkindt's Avatar
    Join Date
    Sep 2009
    Lethbridge, AB, Canada
    Usually the timing is set using timing marks on the flywheel when the front cover is removed. (Static timing)
    Do a search, there is lots of information about it here.

  10. #10
    Lake Mead Bum & BTLS Mark starflight's Avatar
    Join Date
    May 2007
    Boulder City, NV
    I didn't hear any backfiring in the video. Have ya checked the crank index yet?
    I couldn't tell from the video whether or not you have a choke still on the carbs. If you do, try choking a little and see if it'll rev up any better. Also when you went through the carbs, did you check popoff pressure? If a float valve or two are stuck open and not seating, it would flood and run like that, also wetting the plugs.

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