1978 Yamaha ET 250 - Spark Issues - HELP!
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1978 Yamaha ET 250 - Spark Issues - HELP!

This is a discussion on 1978 Yamaha ET 250 - Spark Issues - HELP! within the Vintage forums, part of the Snowmobiles category; Hello, New here and i am stumped on this sled.. i really need some help or input from you guys.. I have a 1978 yamaha ...

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Thread: 1978 Yamaha ET 250 - Spark Issues - HELP!

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    Exclamation 1978 Yamaha ET 250 - Spark Issues - HELP!

    Hello,

    New here and i am stumped on this sled.. i really need some help or input from you guys..
    I have a 1978 yamaha ET 250.. and i'm having spark problems.
    This is the scenario... Sled will run fine.. all day long until you shut it off... when it is shut off it will not start again. the plug is internally shorted - wont spark grounded - sparks from everywhere on the plug in air - install new plug.. runs fine until you shut it off.. plug internally shorted. I have replaced the points - same situation - replaced condenser - same situation - replaced coil.. new coil does not generate enough spark to fire..
    so i have run the old coil which seems to be throwing alot of spark - possibly too much
    wondering if the new coil i got is not the right coil (only identifying numbers on new coil are e9rv- the original coil is CM61-20)
    wire harness looks fine and the situation is the same with teather unplugged the key unplugged and the kill switch unplugged.. only ground is a wire from stator to coil.. have tried extra grounds - motor and frame - same issue.
    Anyone had an issue similar or know what the problem could be.. it keeps pointing back to the coil.. i was told the coil i bought will work.. i took it back and exchanged it for another.. maybe a bum coil...same thing.. weak spark from the both new coils and strong spark from the old coil. i dont have the equipment to test coils.
    the stator looks to be fine - lights work so the internal lighting coil should be good - internal source coil looks ok.. if it was no good the sled should shut down by itself then start again when the coil cools should it not?

    any help or ideas would be appreciated..

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    Not sure about this sled but generally...Check the resistance on both the new and old coils and the stator. The old and new coil resistance should be in the same ballpark. You will need to know the tolerances to accurately test them. I have had coils and stators test fine until the sled has been run a bit. Test both cold (room temp) and warm, letting the sled sit at idle might not get it warm enough. I generally have spare CDI's or coils to swap and will buy a used coil from a reputable seller either locally or on Ebay before I pull a flywheel. Electrical problems often times require the mundane process of elimination and its usually something simple, like a poor connector or bad ground. I had a Bearcat that was driving me nuts and it turned out to be a loose connection where the CDI plugs into the coils. It looked fine, I must have missed it a half dozen times when I was inspecting the connectors. I only found it because it was dark and I saw it arc inside the connection when I shook the harness. Are you shutting the sled down with a key or kill switch? Try both.

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