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  1. #1

    1998 XL1200 running issues

    So I've got two skis, a 1998 XL1200 and a 1997 GP1200. The GP runs awesome for a few hours then it'll start acting up. Doesn't want to accelerate, won't rev past 3,000 rpm and won't go more than 20mph. The XL1200 will run great for about a half hour then just bog out and go to an idle. It will do part throttle up to 3k rpm but no more than that or it bogs and dies. Same if you go WOT on the XL. I've went through the carbs on each ski 4 times. I'm tired of taking these things off.

    Things I've done:

    replaced fuel filters (did not use OEM, could this be the cause?) its a in-line small copper 100micron filter.
    deleted oil pumps, running premix. i ran heavy (32:1) as skis were sitting in a field for 3 years un touched.
    replaced spark plugs (even tried replacing when they were acting up) they were a little moist with oil but not crazy.
    compression tested engines and they are both at 105 across the board.
    visually inspected reed valves with an inspection camera, did not remove manifold
    rebuilt the carbs, replaced on entire stack and rebuilt on the GP; did not use genuine mikuni kits.
    did not replace any of the N/S - none of the venturi are dribbling though.
    replaced all the o-rings on the adjustment needles and cleaned out the passages, returned adj screws to factory (L1;H1.5)

    this issue is becoming increasingly frustrating. i've pulled the carbs and pumps and checked the diaphragms all check out ok. if anyone could help i would really appreciate it.

    edit: the XL i tied up to a tree with the spark arrester off to check to see if the carb was dribbling or not. it got it up to half throttle and then full throttle and it seemed like not much fuel coming from the high speed side. is this how they should be?

    they run fine on the hose but i don't run them very long on the hose and it seems like more fuel flows out on the hose than in the water.
    Last edited by red96turbols; 06-25-2015 at 10:17 AM. Reason: added additional text


  2. #2
    dockwalker's Avatar
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    Much as I know you do not want to hear this, You MUST use Genuine Mikuni carb kits.

  3. #3
    Yamaha artisan Cutlass's Avatar
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    Do they run good after the carb rebuild, then crap out? Or do they run good from every cold start, then crap out as they warm up?
    Few thoughts bouncing around in my head.
    1)Genuine Mikuni kits are a must. Its been proven here, time and time again.
    2)Your compression is low at 105. The further away from the stock 120 you get, the worse the engine will run because the carbs operation are super dependent on engine condition. The carbs need a strong pulse for the pumps, but it the rings are letting too much blowby past them, it'll pressurize the crankcase too much and create an overly strong pulse and ruin the pumps or crease the check valves. On the other side of the carb, strong suction of airflow through the carbs creates vacuum the carb needs to operate those circuits. low compression, low vacuum signal through the carbs.

  4. #4
    The GP runs great for around 3 hours or so then starts to act like its not getting fuel.

    Both skis I used the exact same SBT kits (after i read not to use them).

    The XL is hit or miss. it'll run great for 10 minutes or an hour.

    I spoke with the service techs at the Yami shop up here in Denver and all of them said the compression is about right for this elevation, I also didn't hold it WOT while testing, it was late - i was tired and frustrated.

    They feel like they aren't getting fuel. I really don't want to rebuild the carbs again, though, I've had them out so many times I can do it in an hour. Its the money and the fact I'm new to skis and don't know where to buy parts online.

  5. #5
    would these be a good kit?

    http://osdparts.com/index.php?main_p...oducts_id=3386

    anyone willing to bet money this fixes it?

  6. #6
    could a bad fuel tank check valve be causing a negative pressure in the tank reducing fuel output?

  7. #7
    Yamaha artisan Cutlass's Avatar
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    Quote Originally Posted by red96turbols View Post
    I spoke with the service techs at the Yami shop up here in Denver and all of them said the compression is about right for this elevation, I also didn't hold it WOT while testing,
    Ok, good to know. I'm comfortable with the engine condition then.
    Quote Originally Posted by red96turbols View Post
    would these be a good kit?

    http://osdparts.com/index.php?main_p...oducts_id=3386

    anyone willing to bet money this fixes it?
    I personally wouldn't buy that kit, because I can't really tell if its OEM. No guarantees Mikuni kits will fix it...but you have to start somewhere.
    Quote Originally Posted by red96turbols View Post
    could a bad fuel tank check valve be causing a negative pressure in the tank reducing fuel output?
    Easy to test, loosen up or remove the fuel cap when the ski starts running funny. That'll release the negative pressure if its the problem

  8. #8
    Quote Originally Posted by Cutlass View Post
    Quote Originally Posted by red96turbols View Post
    I spoke with the service techs at the Yami shop up here in Denver and all of them said the compression is about right for this elevation, I also didn't hold it WOT while testing,
    Ok, good to know. I'm comfortable with the engine condition then.
    Quote Originally Posted by red96turbols View Post
    would these be a good kit?

    http://osdparts.com/index.php?main_p...oducts_id=3386

    anyone willing to bet money this fixes it?
    I personally wouldn't buy that kit, because I can't really tell if its OEM. No guarantees Mikuni kits will fix it...but you have to start somewhere.
    Quote Originally Posted by red96turbols View Post
    could a bad fuel tank check valve be causing a negative pressure in the tank reducing fuel output?
    Easy to test, loosen up or remove the fuel cap when the ski starts running funny. That'll release the negative pressure if its the problem

    I re did the compression test just now. 105psi on all 3 cylinders. I checked the pulse lines from crank case, all in good condition and firm, no floppies there or cracks, etc. hit the starter button covering each pulse line with a finger and they all feel pretty firm and equal pressure coming from all three.

    I ordered that kit, they said its all OEM Mikuni aside from needle and seat but i clicked the "OEM N/S" check box for OEM ones. I've read a few people who've used the OSD kits with great success.

    I also pulled off the coupler cover and checked that rear seal - its still in there. no play or anything either (if this is the location of the seal i've read about)

    I used my bore scope, again, to inspect the reeds and they look intact from the outside.

    the plugs were a bit wet with oil, however, i doubt running it rich on oil is causing this as when it started acting up at the lake i swapped plugs and it had no effect on its running. I'm going with carbs on this one.

    I just tried to do test pop off pressure again and the seals on the fuel pumps are leaking at like 14 psi. > this has to be the issue. pulling air instead of fuel.

    I'm only going to rebuild this ski with the OSD kit for now, though i ordered two kits, just to verify the issue is resolved. I'm replacing all the fuel lines too just for good measure.

    On a side note, no one ever answered my question about using an aftermarket, small, inline 100 micron copper core fuel filter vs the OEM yamaha water separator... any one? it looks like this:

    Click image for larger version. 

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  9. #9
    GGG's Avatar
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    Do not use that filter it doesn't flow anywhere near enough fuel. Your compression is too low so you probably have scored up pistons. And I have probably rebuilt over 200 mikuni sbn carbs and have never used a mikuni rebuilt kit. Needle and seat I use mikuni but not the rebuild kit

  10. #10
    the SBT rebuild kits were iffy. they weren't cut properly on some of the gaskets and they are leaking from the fuel pump and yes, the bolts are tight.

    fuel filter axed. thanks.

    again this compression test is done with a cold engine at 5280 feet. 120 psi at 101.6 kpa at sea level (where all specs are derived from) vs denvers 83.4 kpa will yeild a lower result. i doubt the engine is to blame.

    120 * .8359 = 100psi. engine is at spec at this altitude.

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