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  1. #1

    Low speed tuning help needed - SUV1200

    So I went out yesterday to break in a new top end on a '00 SUV1200, 65u npv. The only mods are drilled out return and tau Ceti tornado flame arrestors with no air box. I'm premix mineral oil at 32:1 and elevation of 7,000'.
    I had the carbs set as suggested:
    135 mains
    100 lows
    1.5 n/s with 115g spring
    Pop off around 60
    I just rebuilt them with genuine mikuni kits.

    *I've read so many posts, the mikuni tuning guide and more and it has my mind running in circles*

    The ski was fine to start with since I was only doing short blips to 1/4 throttle. As I began to move up the throttle use, it would die/or start to die around 3-4K. If I slowly took it to 4K and tried to hold speed it would "pup pup pup pup and rpms would drop quickly, no response to throttle. If I hit it harder at half to 3/4 throttle it would die.

    I checked the new plugs and they were wet.

    So the plugs are wet but the symptoms described a lean condition? I backed out the high speed screws and between 2 to 2 1/2 out it fixed the 1/2 to 3/4 throttle dying problem. At that point, the low end sucked but the magical 4K area would be an immediate "kick in" and it had that shifting gear feel and rpms went up and the ski would take off hard. I never went WOT since I'm still finishing the breakin but I am following mototune and started running it 3/4 to get up around 35 mph and hard deceleration. I had no apparent running problems after the "kick in". That's fine but it was like two different skis... wuuuuuuu (kick) WEEEEEEEEEEEEEEEEEEE!!!!!

    Back down at idle and through light throttle, it wasn't responsive. The more I backed out the low speed screw, the better it would respond. I was able to get it to hold rpms at 3k and 4K without it falling but I'm so many turns out that I'm only in far enough to keep them seated. It's still not right. It is more "consistent" in holding rpms and I can vary the throttle without noticeable spurts or sputtering.

    Through this process, I had to keep tightening the idle screw because the idle rpms would get so low. It also wouldn't start without me giving it some throttle.

    I checked the plugs and they were dry this time...

    This has so many variables that I'm feeling lost and not sure where to go next. I really expected it to be too rich to begin with due to elevation.

    I was wondering if my popoff is too high. Need larger pilot jet?

    I need to go out this morning and get more break in time and fix this issue. Any suggestions on how to troubleshoot this from here?? I'm holding out hope I can get an aftermarket tach this morning.

    I'm in a remote mountain town in CO where jet skis are like ufos and there are no shops to rely on. I'm on my own. I'm thankful for any help to get me down the right path.

  2. #2
    Yamaha artisan Cutlass's Avatar
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    I would suggest lowering your pop off to lower 50s psi area.

  3. #3
    For the engineering brains...

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  4. #4
    Quote Originally Posted by Cutlass View Post
    I would suggest lowering your pop off to lower 50s psi area.
    Thanks again for your help Cutlass. Can you tell me what to look for after adjusting it down? Should I start back at the base adjustment settings?

  5. #5
    Yamaha artisan Cutlass's Avatar
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    I would put both screws back to a base setting and do the same thing as before....back them out if needed

  6. #6
    Yamaha artisan Cutlass's Avatar
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    The lower pop off should richen the off idle to 30% or 40% range, which is what you were sort of accomplishing with the screws

  7. #7
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ID:	418886So I pulled the plugs this morning and they're soaked...

  8. #8
    Yamaha artisan Cutlass's Avatar
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    Your idle is probably really rich and soaked the plugs as you idled back to the dock

  9. #9
    jeffg426690's Avatar
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    The 32:1 ratio isn't helping things either, that's a lot of oil and consequently less fuel. If that's not the ratio you are staying with, don't try to adjust and tune with it. Typical premix seems to be favored at 40:1, some mix up to 50:1 or somewhere in between.

    Think about it though... Your carbs allow 'x' amount of volume through them, regardless of what it consists of, if you have more oil in that volume, you have less fuel going into the cylinder for combustion. 40:1 is just fine for break-in.

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  11. #10
    Quote Originally Posted by jeffg426690 View Post
    The 32:1 ratio isn't helping things either, that's a lot of oil and consequently less fuel. If that's not the ratio you are staying with, don't try to adjust and tune with it. Typical premix seems to be favored at 40:1, some mix up to 50:1 or somewhere in between.

    Think about it though... Your carbs allow 'x' amount of volume through them, regardless of what it consists of, if you have more oil in that volume, you have less fuel going into the cylinder for combustion. 40:1 is just fine for break-in.
    Thanks, good point!

    Is it possible my flame arrestors with no air box could be making it too lean without rejetting? It's just the three cones directly onto the carbs. They're too big for the air box.

    I was back out today after lowering the popoff to around 50-52, reset the screws back to the recipe. It ran great for about the first 15 minutes and then started the same symptoms as yesterday. Initially the throttle was crisp, had a good idle and accelerated more smoothly. Then it started the low speed non-responsiveness. It just didn't want to accelerate. The throttle needed to be opened about 3/4 to get out of the lows and it would kick in. Then, again from a stop, it completely died at 3/4 throttle starting at about 3,000 rpm. It would hit that consistent ceiling and drop rpms quickly. I tried enrichening the low speed mix a 1/4 at a time and could never get it out of the two extremes, seemingly too rich or too lean. Just no consistency to narrow it down. Once out of the low end, it would open up at about 4,000 rpm and take off. A couple of
    Times it had lean symptoms accelerating, wanting to die with throttle, exhaust popping. I'd richen it slowly and it just ran like *hit. I'd watch the plugs and I could get it rich enough to wet them and then go leaner just to get that same behavior, not wanting to accelerate, popping and poor response.

    There was no seeet spot, it seemed to have all changed after running about 10 - 15 minutes.

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