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  1. #1

    95 SLT 750 low end bog

    Well Hulksters ive been sneaking around the forums last few months. Decided time to register and ask the pros. I have searched these forums prior to posting

    I gutted a 1995 SLT 750 and am using original wiring,fuel system,pump and motor in a 10' Mini Jet boat.

    PTO side had bad rings and cylinder. Had all 3 punched 1 over, new pistons and rings,Crank indexed and good. Did a full rebuild,seals, 3 crank gaskets, the whole shebang. 120# compression on all 3, new battery and stator tests good and new BPR8ES plugs.

    New fuel lines and 3 carb rebuild kits (Genuine Mikuni kits) and bought a pop off tester and am at 12-17# on popoff, High and low speed screws set to stock. Yes, i used the same fuel restrictor, using a triple outlet blue pump from a 780, also did oil injection delete kit. Running 40:1 91 non ox fuel and yamaha 2 stroke oil.


    Motor starts and idles great, bogs out and dies when given throttle, i can choke my way out of it and it runs great from 1/4 throttle up. Ive backed out low speed to 1 turn with minimal effect. Did a high speed chop and plugs arent wet and are brown and within acceptable range.

    Any ideas or directions Hulkamaniacs?
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  2. #2

    Join Date
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    Sometimes a Stator tests good but fails under load/rpm....working through that myself with the same motor. Carbs/fuel line/fuel pump/coils/plugs/ were all changed but still got my bog although mine is at higher rpm. When I get the Stator change I will post my results...its going to be at least a month from now

  3. #3
    Myself's Avatar
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    Do you have an extra ground wire from e-box to engine or battery negative? If not, add one.

  4. #4
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    If choke fixes it that usually means it is lean. I'd try opening the lows some.

    What am I saying, I would use Randy's tuning method like I always do for rebuilt skis now:

    "Start with the screws set at 1 turn out, and tune with the tachometer for peak Rpm, then stop there and count the number of turns on the high speed screws. Write this down on a piece of paper.. Then turn the high speed screws in all the way and open them to 1/4 turn open. (Now you will be testing starts only, so no more big high rpm trips around the course). You are only turning in the high speeds to allow you to easily tune the low speeds.

    Now check the low speed screws and set them at 1 turn and do a practice start; To test the low speed setting pretend that you just jumped the start and you have to start with no holder. Hold the ski by yourself and hold as many Rpm as you can (don't blow it out first for testing) and then nail the throttle hard.... NO FARTHER THAN 50 FEET, as you are only testing the start response

    If it blubbers like a schoolgirl trying to guzzle a quart of beer, then it's too rich on the low speed screws..
    If it falls flat on the line (like someone punched you in the stomach).. It's too lean on the low speed screws.

    When you like the acceleration off the line, stop there and count the number of turns on the low speed screws. Write this down on a piece of paper.. Then re-set your high speed screw where they show the best peak Rpm earlier and try both a start and a peak Rpm run...
    It will probably "blubber" a little off the line... DO NOT turn in the low speed screws... Instead, go back out on the course and fine tune for peak Rpm again.. The blubbering off the line is caused by having too much fuel in the high speed circuit... Write down your new high speed setting on the piece of paper along with the best low speed setting that you found earlier, this will be your base-line carburetor settings.
    If the high or low speed screws are open more than 11/4 turns, then you need to swap to the next bigger jet.
    If the high or low speed screws are closed all the way, then you need to change to the next size smaller jet."

  5. #5

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    Thanks for the info on "Randy's tuning method".....it's foolproof and brilliant

  6. #6
    RLACEMAN's Avatar
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    Increase main jet & low speed jets by one size, these engines were designed to run on fuel of 25 years ago. I had the same issue on my SLT, screws were out as far as they could be effective, increased main jet one size & pilots 1 size bog was gone. The carbs are easy to get to in your application unlike in the SLT.

  7. #7
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Quote Originally Posted by RLACEMAN View Post
    Increase main jet & low speed jets by one size, these engines were designed to run on fuel of 25 years ago. I had the same issue on my SLT, screws were out as far as they could be effective, increased main jet one size & pilots 1 size bog was gone. The carbs are easy to get to in your application unlike in the SLT.
    Yep, I drill all the jets one size over on any carbs I rebuild now. Easier to screw them in than have them tuned but about to fall out.

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