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  1. #1
    Pro-pulsion's Avatar
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    Running out of ideas here.

    Ok, so my ski won't stay running anymore and it's getting very frustrating. I put in a rebuild kit for the fuel pump (was actually a carb kit but missing the metering diaphragm), drained the fuel and dried up the tank, put in a lower pop-off weight needle valve spring and made a new intake gasket with some premium gasket paper. When I first modified the engine and re-assembled it it ran perfect for over two hours. I ended up having enough for the day and pulled it from the lake. The second time I took it out it ran great for about an hour, hour and a half and started acting up, it would just shut down as if someone was tagging the kill switch. So I took it out on Sunday and it worked awesome for a half an hour or so before acting up again.

    Monday it lasted 2 minutes and started acting up, it did this as well 3 weeks ago at a big freeride event I drove hours to get to! I never had more then 10 minutes of total run time out of it. As mentioned, it acted like someone touched the kill switch and it would shut down. This has happened at various times, high speed, throttling up, blipping off of idle, etc., but all at random times, never the same engine load or speed. Sometimes I could get 30 or more seconds of mid to top end then it would shut down, sometimes it would do it right after a restart and building up to plane. So at first I thought it might be the kill switch. I took that apart and checked everything there and found no problems. Now I'm thinking either there is a lot more wrong with my carb like something movable is in a port and will sometimes flip sideways closing off the port, or a throttle butterfly shaft is worn out, or my crank seals are toast.

    It will run really well and get up to top end with no troubles, then like flicking a switch it shuts down...sometimes I can start it right up while still standing as I coast down to a stop and other times I have to choke it to fire it up. I'm really thinking the carb is the problem. I did notice that the O-rings would swell up and expand a lot...like a quarter of an inch a lot, and go back to normal when they dried, would the original fuel lines swell shut like that cutting off my fuel enough to kill it? I have by-passed the fuel selector valve and taken the one way tank vent out of the loop entirely with no changes, plus it always has a slight bog when cracking it.

    The new needle valve spring seems to have helped reduce the bog but it is still slightly there. The plugs look good and are burning a nice chocolate brown. I have put in a new head gasket, exhaust manifold gasket, reed cage gaskets, cylinder base gasket, intake manifold gasket, carb kit, new fuel, pop-off spring, needle valve and spark plugs. Any idea what else to look into? Anyone have a 42mm carb that will work on my 92 650SX ski they want to sell nice and cheap?


  2. #2

    Smile

    if you have to choke it to start it after it dies its for sure a fuel problem, did you clean petcock out when you rebuilt carb?did you check lines going into fuel tank?The pickups in fuel tank?lots of things to try and not enough info>Marvin

  3. #3
    Pro-pulsion's Avatar
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    The pickups in the tank look good, the lines are the original ones but are still soft and look to be in good condition. I did bypass the petcock the first day it started doing this but there was no change.

  4. #4
    pokechop2006's Avatar
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    how about your homemade gaskets,ive never had luck with that.

  5. #5
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    check all of your electrical contacts in the switch assembly.

    Sean

  6. #6
    Pro-pulsion's Avatar
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    interceptor 150:
    I thought about the homemade gaskets too but it was perfect when I first rebuilt everything. I was using OMC GelSeal (anaerobic flange sealant) with the original gasket after the rebuild and I thought it didn't pan out. After that I re-sealed the original gasket with a silicone sealant and no change in the issue still, and then a homemade gasket and still no changes so I'm pretty sure that the homemade job is holding up alright. I've actually had really good luck with making my own gaskets

    smokeysevin:
    I didn't go into a long drawn out diagnostic of the switch assembly but when the problem first arose I tested it to make sure the continuity and resistance values were good. This past weekend I took the handlebar mounted assembly apart to check the contacting surfaces for anything obvious but all is well there too.

    Thanks a ton though guys, I'm really appreciating the suggestions and please keep them coming. I took apart the carb tonight under a suspicion and I was right, I was wondering if the throttle butterfly shaft had worn out bushings and did it ever. There was at least a milimeter if not two of play between the shaft and the I.D. of the bushings. Would this be the gremlin I've been hunting for? I know I have seen this problem before on a chainsaw carb but it didn't cause this kind of trouble, it just made propper tuning impossible. The saw would still run though. I do know that the ski will idle all day but as soon as I start playing with the throttle it will bog and die. It just seems hard to believe that there is that much air getting past the bushings to drop the engine so easily and quickly. What do y'all think?

  7. #7

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    I would think that since there is a lot less air passing the plate at idle, the air that was leaking from the shaft would give you problems there. When you have the throttle open I'd think that the large amount of air flowing at that point would make the relatively small amount that was getting past the shaft insignificant.

    John

  8. #8
    qbzonk's Avatar
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    Have you opened the gas cap after she shuts down to hear for a "Whoosh"?

    What springs did you go with 65g 80g....?

    Did you measure ure pop-off pressure?

    Does she run hot?

    Have you checked the carb internal filter?

  9. #9
    Pro-pulsion's Avatar
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    I'm not sure what the pop off pressure is, I don't have a tester for it. I went with a spring that has a slightly tighter coiling to it instead of the stock spring. It was one of three springs inside the carb kit I bought. It does run hot, hotter than stock anyway. You can't hold your hand on the engine but it's not hot enough to boil any water that drops onto the head. For the fuel cap, usually I get a bit of a pressure release when I crack open the cap, not an intake sound. I know that if it was the in taking whoosh that I would have to replace the one way valve because it's not allowing air into the tank. But the valve is good and the screen inside I've cleaned out each time I removed the carb. It was never dirty after the first time I cleaned the carb but I figured that since I was there to just do it again anyway.

    Getting back to the temp though, I don't believe the temp would be an issue because it ran at these temps for over 2 hours the first time I took it out without and troubles, and about an hour the second time trouble free. If it was temp related, shouldn't it have shown up at about the same time every time when things came up to a certain degree? This issue would happen at random, on a hot engine after a half an hour of run time (like this past weekend) or even 10 seconds off of the first start of the day.

  10. #10
    qbzonk's Avatar
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    I just paid the money for a pop off pressure gauge myself. It solved my carb problems I was trying to diagnose on my boss' ski. Worked like a champ.

    Here is a do it yourself version: http://www.kartingtechinfo.com/tech/popoff.htm

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