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340 Rotax, no fire

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  • 340 Rotax, no fire

    After getting out of snowmobiling for a few years I decided to let my brother use my '77 Nuvik. It ran well when I parked it and pulled the motor to redo the top end because it was really low on compression (less than 100 psi). It has been sitting in my basement for 5 or 6 years until last week when I replaced the top end on it.
    When I got it all back together I figured I would make sure it was firing before we put it back on the chassis and had no spark on either side. I tried different plugs and wires but it made no difference. If I unhook the wires coming from the stator from the coil and check them, I'm getting fire but I'm guessing it's not enough. When I check it with a test light, it seems plenty bright but I don't know exactly how many volts there is at that point. However, as soon as I hook the wire to the coil, the test light becomes very dim when I crank it over, which makes me think I might not be getting enough volts from the stator.
    I tried cleaning the points and blowing everything out under with there compressed air (even though everything was perfectly clean anyways) but it made no difference. It's frustrating because firing problems was absolutely the last problem I thought would have since there were no issues when I took the motor off and I didn't touch anything firing related except for taking the wires off the coils when I took the cover off that the coils bolt to.
    The only think I can think of causing the problem could be a weak pickup coil under the stator or it too close or far away from the magneto. How much of a gap should there be?

  • #2
    1) Unplug the engine from the sled. 2) make sure grounds are correct and in good shape 3) try it again - still no spark - points are corroded or condensers have given up. Take some emery to the points and see if that helps. Coil to flywheel distance is fixed. Points engines don't like resistor spark plugs, resistor wires or resistor caps. Copper core wire, spark plugs without an R in the number and NOT ngk plug boots/wires

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    • #3
      Filed the points again and I now have fire. Hopefully I'll get it installed over the weekend.

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      • #4
        I finally got around to getting it installed after stripping a plug hole and having to replace a head. I put a couple miles on it today and it's working fine so far. At this rate, I won't even get it broken in this winter.

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        • #5
          I have a new problem. I put a few gallons of gas through it with no problems but then it suddenly started to want to flood out. I thought it might have been sucking gas through the fuel pump so I replaced the pump but that didn't help. It has a clear line so I can see that there is no gas flowing through the pulse line. Then I thought it might be sucking gas through the primer so I blocked that off but that didn't help. Lastly, I thought a welch plug might have popped out but when I took the carburetor apart, everything was as it should be. It seems to be ok if you're going at full speed but dies as soon as you slow down.
          Also, it won't stay running unless the high speed jet is out roughly 3 turns (the manual says 1 turn +/- 1/4 turn. Could a carburetor be worn out badly enough for it to flood out like that or could it be something else?
          The carburetor setup I have is a Tillotson from a 340 TNT with a blockoff plate on bottom and an external Mikuni pump. I've ran this setup for at least 5 years with no real problems. Maybe it's time for a rebuild?
          Last edited by bvolks; 03-06-2018, 10:04 PM.

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          • #6
            Some additional information. It started right up today and idled for several minutes with no issues. I could rev it up enough for the clutch to engage with no issues but when I raised the back and ran it at high rpms for a few seconds, it would flood out and die when I let it come back to an idle. It seems like I could idle it all day with no problems.

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            • #7
              a wise man once told me " rebuilding a tilliston carb was a **** shoot" on whether it worked after... something about plugs
              out of holes and balls that were no longer blocking passages ......This sounds like one of them things
              Ron

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              • #8
                Swapping out the top diaphragm (the only one in the setup I have) fixed the problem. The one I took out was as stiff as tar paper. I think it's time for a carburetor kit.

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