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  1. #1

    Interpretation and advice on piston wash

    Good afternoon. I hope everybody had a great summer. So I've been working on this 1995 SL650STD for a little while now but I can't quite get everything dialed in. All three carburetors were recently rebuilt with genuine Mikuni rebuild kits. Popoff was set around 19 psi. Compression is a little low at 105 psi across all three cylinders but I'm not 100% sure if the compression tester I have is correct. It was a loaner from AutoZone. The spark plugs are NGK BPR7ES brand new and gapped at .028". Mag carb high speed 1 1/8, center 1/4, and pto 7/8. Low speed at 1 1/8. While parked on the trailer in water and also underway Max RPM is only around 3800 rpm at WOT. So I kept it on the trailer WOT for about 1 minute and I stopped the engine. I pull the heads off to look at the Piston wash and I look like I'm rich across all three. Also, both magneto and center spark plug are a light brown and the PTO was dark and not quite soaking wet but it did have a slight wet film on it. Your interpretations and advice will be greatly appreciated.Click image for larger version. 

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  2. #2
    Click avatar for tech links/info K447's Avatar
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    RPM is way down from where it should be at wide open.

    Have you trimmed the spark plug wires back about 1/4" and rescrewed the plug caps onto the wires?

    What impeller part number is in the jet pump?

    Was the on-trailer test running with the seat removed? Any signs of exhaust leaks?

    Have you inspected the exhaust hoses for possible soft areas or internal delamination?

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Keith is right, RPM is way too low.

    Tough to tell from your pics, but something doesn't seem right.

    Your studs missing is odd. And it looks like you've re-used those head gaskets a few times already.

    My gut feeling is you're ingesting cooling water into the cylinders which would "steam clean" your piston domes (remove wash pattern) and give lower RPM readings.

    My suggestion would be to clean/chase your cylinder threads and properly install your studs with loctite.

    Completely remove any old gasket material from your heads and cylinders.

    Buy new head gaskets and make sure they are installed properly. (there is a specific direction they must be installed)

    Lastly, I hate to ask, but I must. Are you sure those are 650 heads? (750 will bolt right up, but will give low compression readings)

  4. #4
    Quote Originally Posted by K447 View Post
    RPM is way down from where it should be at wide open.

    Have you trimmed the spark plug wires back about 1/4" and rescrewed the plug caps onto the wires?

    What impeller part number is in the jet pump?

    Was the on-trailer test running with the seat removed? Any signs of exhaust leaks?

    Have you inspected the exhaust hoses for possible soft areas or internal delamination?
    1. Yes
    2. Unknown. I've only owned the watercraft for about 10 months
    3. Seat was slid back enough to reach all 3 plugs. When I did slide back the seat there was exhaust smoke in the engine compartment but not sure where it was coming from.
    4. I have not but I will and post results.

  5. #5
    Quote Originally Posted by xlint89 View Post
    Keith is right, RPM is way too low.

    Tough to tell from your pics, but something doesn't seem right.

    Your studs missing is odd. And it looks like you've re-used those head gaskets a few times already.

    My gut feeling is you're ingesting cooling water into the cylinders which would "steam clean" your piston domes (remove wash pattern) and give lower RPM readings.

    My suggestion would be to clean/chase your cylinder threads and properly install your studs with loctite.

    Completely remove any old gasket material from your heads and cylinders.

    Buy new head gaskets and make sure they are installed properly. (there is a specific direction they must be installed)

    Lastly, I hate to ask, but I must. Are you sure those are 650 heads? (750 will bolt right up, but will give low compression readings)
    When I removed the heads some of the nuts came off and on some the entire stud came out. Today was the first time I've removed the heads and not sure about what the previous owners did. I have new head gaskets on order and I will ensure they are installed correctly.

    Not sure about the heads. I've only owned the watercraft for about 10 months and this was the first I removed the heads.

    Thanks, I appreciate your time. I'm going to check the exhaust hoses as stated above and I will replace the head gaskets.

  6. #6
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by bart98stang View Post
    ... there was exhaust smoke in the engine compartment but not sure where it was coming from.

    4. I have not but I will and post results.
    Exhaust smoke source inside the hull needs to be found and corrected. There should be zero exhaust inside the hull.

    No point in keeping the seat on at all while investigating the exhaust leak(s). Do not assume there is only one exhaust leak or damaged exhaust hose section.

    Check all the exhaust hoses, but start with the rubber hose section nearest the engine exhaust pipe. If the exhaust water injection spray orifice is clogged the exhaust hose nearest the engine will become quite hot and most likely to melt or burn internally.

    There is a special small hole that feeds cooling water directly into the flow of hot exhaust gases just before the exhaust flow exits the metal exhaust pipe. That water orifice on the blue Fuji engine is hidden inside the water jacket, IIRC. There are threads posted showing where it is located and how to make sure it is clear.

  7. #7
    Quote Originally Posted by K447 View Post
    Exhaust smoke source inside the hull needs to be found and corrected. There should be zero exhaust inside the hull.

    No point in keeping the seat on at all while investigating the exhaust leak(s). Do not assume there is only one exhaust leak or damaged exhaust hose section.

    Check all the exhaust hoses, but start with the rubber hose section nearest the engine exhaust pipe. If the exhaust water injection spray orifice is clogged the exhaust hose nearest the engine will become quite hot and most likely to melt or burn internally.

    There is a special small hole that feeds cooling water directly into the flow of hot exhaust gases just before the exhaust flow exits the metal exhaust pipe. That water orifice on the blue Fuji engine is hidden inside the water jacket, IIRC. There are threads posted showing where it is located and how to make sure it is clear.
    Gotcha. Thank you. While waiting for the new gaskets I'll investigate the exhaust leak. Also, I've read about the oriface before so I'll find the post and ensure it's clean.

  8. #8
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    It does appear the rear cylinder is ingesting a bit of water. The wash pattern appears more dry on the carbon and the matching head is also too clean. You are running a little rich especially on the front cylinder.

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