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Thread: Kinda stumped

  1. #1

    Kinda stumped

    I'm actually a long time lurker, just never a poster. I'm also not a stranger to 2 strokes, PWC, boat engines, BN/SBN carbs, etc etc. I do, however, have a real headache that I just cannot seem to figure out. I'm hoping that someone else has had this issue on one of these machines before and can offer some insight.

    First, a little background. I got the ski (basically) in pieces in trade from some Mercruiser SBC parts. It's a 1992 SL650 nearly completely stock, rode hard and put up wet. Center cylinder was scorched (but the other two weren't far behind) so I ordered a WSM top end kit. I disassembled the entire engine because it also needed a PTO end crank bearing from sitting and I threw in crank seals just for good measure. I bored out all three cylinders and pressed on the new bearing (I do all my own machine work). Reassembled the engine and set it to the side while I took care of several other issues. I replaced all of the fuel lines, disassembled and cleaned all three carbs, deleted the oil injection, rebuilt the fuel pump (I did not do the triple outlet, had already ordered the stock rebuild kit), and checked out the pump bearings.

    Once I dropped the engine in the hull, it fired right up. I took it to the lake and it ran but not really well. It had a bad flat spot about 1/2 throttle that some finesse with the throttle or a quick blip of the choke would get it through. Once it was running top end, it was running crisp and clean and clocked 41 mph on the GPS. I was, however, very pleased that I had brought it back from the dead. I figured a little carburetor tuning and we'd be right as rain. Oh boy was I wrong....

    I have gone back through the carburetors left to right, front to back, adjusted the hi and lo speed needles until I am blue in the face, checked the pop-off pressure....twice. I built a return line restictor, took out the fuel filter, moved the fuel filter, deleted the fuel filter. I took the fuel pump down several times (the brand new rubber hoses are getting wear marks on the ends from the clamps).

    Now for the nitty gritty's:

    "Early" 92 SL650 everything stock on the machine except for the intake elbow (off a later model instead of the big goofy box but I've tried it with it, without it doesn't matter). Rebuilt DF52 and #63 drilled return line restrictor. Carburetor settings at Clymer's manual set points for the "early" 92. Pop-off pressure at 26-27 psi.

    It starts and idles fine. It will begin to accelerate and at about 1/4 throttle it begins to bog down. If you pop the choke, it will pick up and you can quickly apply full throttle and it will rev completely out. I know what you're thinking, OBVIOUSLY it's lean and starving for gas (same thing I thought). I finally broke down this morning and ran it sitting in the lake strapped to the trailer with the flame arrestor off. Looking down each carburetor throat, it's not starving for fuel at all. The carb's open and fuel starts to come out into the venturi and the engine just starts to wither away. The carburetors never stop delivering fuel through the main circuit and the few times it does pick up RPM properly, it looks exactly like the times it doesn't. I sat at the local boat ramp for half an hour today just looking down the carburetor throats and wondering what sort of a mess I have gotten myself into... I came home today convinced that it MUST be an ignition problem so I pulled the engine to check out the stator and flywheel. I removed it expecting a large build up of metal "fuzz" on the timing coil but found nothing of note... I did clean it all up again, just for giggles and tested the stator (of course, it all tested out in spec) and reinstalled the engine into the hull. I didn't test fire it tonight but I intend to take it to the boat ramp again tomorrow and see how it does.

    I should also note that all three spark plugs are a nice, even dark brown and all three cylinders are at 120 psi still.

    Anyone have any specific insight into what else could be wrong with this machine? (other than the obvious demon possession)

  2. #2
    Banned User
    Join Date
    Jun 2010
    Milwaukee WI
    If it bogs at 1/4 throttle, Im going to guess either your popoff is too high, or you need to go up on the low speed jet. Its starving for fuel in that range. Visually looking down the carb throat will not tell you if its getting enough fuel or the right mixture.

    Read this......

  3. #3
    Join Date
    Jul 2007
    Cedar Rapids,Iowa
    If timing is on then your dealing with a carb issue. The 650 was the early test pig. Check the jetting in the latest 650 made.they may have upped the jetting. I think you can also trade up to the 750 cdi with a better timing curve.

  4. #4
    I had a LONG day on Friday. I took it to the lake and proved that no amount of jetting adjustment would help. I ripped them back off and set the setpoints according to my manual.

    I am convinced that there is no way that a non-double jointed human being can do a dynamic timing test in the hull. I just went ahead and ripped the engine out of the hull. I pulled the flywheel off and checked the stator plate position. I had set it back to where it came off from which is with the line (my stator plate only had one line while the manual shows two) about a millimeter above the case mating surface. I held up my degree wheel to get an idea of what the adjustment range was and turned it 6 degrees counterclockwise. I then dropped the engine back into the hull and hooked it back up. I was out in the shop until the wee hours of the night getting that thing all back together. At this point I was so frazzled at this point, I wanted to go sink it and be done.

    We took it out the lake Saturday morning (Waaayyyyyy too early considering the late Friday night) and my wife took off on it. I swear, once it hit the water it never missed another lick....

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