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Snowmobile driving me crazy!


WyattFarmall
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I know this isn’t the right forum to talk about a snowmobile but you guys are pretty smart so I figured I would ask.

I dug a 1971 Sno Jet snowmobile out of the woods and I am trying to get it running. Problem is I only have spark to one cylinder. I replaced the spark plugs and ignition switch, still only one cylinder has spark. I replaced the condenser and points on the bad side, no spark. I made sure it had a good engine ground, no spark. I tested the coil on the bad side with the good side hookup and both coils work. Using a DMM I see both sides get the same voltage and the circuits have continuity. the ONLY thing different is that the bad side has higher resistance. I’m stumped! 

If I missed something, I would appreciate the help.

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Both coils and plug wires work, if I swap the power supply from the left coil(which sparks) to the right coil(which doesn’t), the right coil will spark. Theres a problem somewhere in the power supply to the right coil, which baffles me because I replaced the components (points/condenser) and the voltage on the DMM shows up the same in both circuits.

There is 2 sets of points and 2 condensers because its a twin cylinder.

I’m starting to think that everything is working, but because of the higher resistance in the bad circuit there isn’t enough voltage to cause a spark. 

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Where is your high resistance? The coil? The magneto windings? I'm thinking you have a bad wire going to the coil or a bad winding. What's the resistance difference between the windings? I rigged up an automotive l.e.d. light on a wire and alligator clips. It doesn't use much current to light up, because it's l.e.d., but it will flash on and off if you have good points and windings. Test before the wires going to the coil, right off the condenser and points. One end on engine ground, the other on the power coming out to the coil. Don't connect them on the coil end of the wire, that way you won't be able to tell what is the matter. Also, wires may show continuity with a meter, but not hold voltage. Unhook the wires and use a batter to apply voltage across the wires. Put battery on one side and a good load, i.e. old incadecent test light on the other. If it doesn't light up, you have a bad wire, if it does, you have a problem on one end of it or the other. Make sure to test both wires with a load, otherwise you will always have a continuity test even if it really is bad. Had this happen to a lot of N14 Cummins engines to supply power to the ECU. Wire would read good, but be bad because of corrosion inside of the wire connector. 

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1 hour ago, MinnesotaFarmall said:

Where is your high resistance? The coil? The magneto windings? I'm thinking you have a bad wire going to the coil or a bad winding. What's the resistance difference between the windings? I rigged up an automotive l.e.d. light on a wire and alligator clips. It doesn't use much current to light up, because it's l.e.d., but it will flash on and off if you have good points and windings. Test before the wires going to the coil, right off the condenser and points. One end on engine ground, the other on the power coming out to the coil. Don't connect them on the coil end of the wire, that way you won't be able to tell what is the matter. Also, wires may show continuity with a meter, but not hold voltage. Unhook the wires and use a batter to apply voltage across the wires. Put battery on one side and a good load, i.e. old incadecent test light on the other. If it doesn't light up, you have a bad wire, if it does, you have a problem on one end of it or the other. Make sure to test both wires with a load, otherwise you will always have a continuity test even if it really is bad. Had this happen to a lot of N14 Cummins engines to supply power to the ECU. Wire would read good, but be bad because of corrosion inside of the wire connector. 

When I tested each coil they had 16,000 ohms and 17,000 ohms. (secondary side) Each one works. When I put one lead at the ignition switch connection and the other at the primary coil connection the working side gets ~10 ohms and the non working side gets ~24 ohms. When I tested from the condensers to the primary coil connection I got right around 0.2 ohms on both. When I put a lead on an engine ground and one on the primary coil hookup, when I pull the cord it fluctuates between 0 and 3 volts, which tells me the points are working. Since each side is producing voltage I think the windings are ok.

I think I’ll test resistance in the wires at every connection to see if its just a wire.

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Harley coils have either 2.8 ohm electronic ignition or 4.2 ohm for points so your resistance is off especially if you compare coil to coil.

This era likely is a Sno jet engine, they then used Yamaha a couple years later and finally Kawasaki.

Your plug wires should be solid core.

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Well it must be your coil. If the bad side magneto will fire the good side coil, it has to be the coil or the high tension lead(plug wire). Also, make sure someone didn't put a carbon core wire on it. Some of the older stuff doesn't have enough power to spark through the carbon wire. It should be a copper wire core in there. If you unscrew it from the coil, it will be obvious what one you have.

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I have a 76 Astro 340 with that same engine, I will see if I can take readings off the coils for you today.

Side note my buddy has 2000 Summit that would single cylinder at times and it turned out the be an intermittent wiring issue in his kill switch.

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On 4/27/2020 at 2:50 PM, WyattFarmall said:

When I tested each coil they had 16,000 ohms and 17,000 ohms. (secondary side) Each one works. When I put one lead at the ignition switch connection and the other at the primary coil connection the working side gets ~10 ohms and the non working side gets ~24 ohms. When I tested from the condensers to the primary coil connection I got right around 0.2 ohms on both. When I put a lead on an engine ground and one on the primary coil hookup, when I pull the cord it fluctuates between 0 and 3 volts, which tells me the points are working. Since each side is producing voltage I think the windings are ok.

I think I’ll test resistance in the wires at every connection to see if its just a wire.

If you try to ohm out a condenser the resistance should climb because the voltage put out by the meter energizes the condenser. If your getting a steady reading you have a bad condenser. Digital meter should climb and read OL.

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I ended up removing the recoil and I looked at the points, and the points were set too close and weren’t opening, so after setting the points it sparks on both. I should have realized that was the problem from the beginning. It sputters but I ended up flooding the engine and I haven’t been able to get it running steady yet.

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