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Discussion Starter · #1 ·
I have a 1993 Yamaha EX570, it was rebuilt. When i start it (after a few pulls) it backfires then dies. What could be causing this problem???
 

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is it an exciterII? if it is we have the same sled! your timeing could be off...im not to familure with the timeing on sleds....but thats what it sounds like to me.But first try replaceing your spark plugs and if that doesnt work replace your cylanoid and plug wires...if that doesnt work then it could be your timeing....im no expert on these things but thats what i would try.
 

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line up the crankshaft timing dot with the camshaft timing dot
 

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2 strokes don't have a camshaft...

Your manual should state how many degrees before TDC your igntion should fire and at what RPM. Then you need a timing light. Then follow your specific manufacturer's instructions on how to check the timing.
 

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Discussion Starter · #5 ·
i noticed that one of the spark plugs has spark but not from tip to tip. its from tip to more towards the inside of the top. Could it be that?
 

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Discussion Starter · #7 ·
it was running fine before, now all of a sudden one day it desides to do the backfiring, so could it still be the timing? i dont think the bolts could have gotten loose,
 

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If your spark plug isn't firing to the electrode, then the plug is fouled out. Replace it, and all should be well again.
 

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Yeah, most definetly replace the plugs, thats always the first thing I do when trying to diag running issues. I keep 3 extra sets in my sled for "Just in case" I usually end up handing them out like halloween candy to my buddies.
 

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im surprised triumph didntsay this, Make sure your choke isnt sticking as that can cause similar problems as well
 

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Bobinwi, thanks for that one, the materials engineering class was approaching very quickly when i posted, didnt have much time, but wanted to try and give a quick response before i left.

Anwyas, Bobinwi is correct here...if your choke is sticking, it could be the reason the plug fouled out in the first place.

TOU
 

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Snively Trader sounds like you might have water in your gas try puting a little Isopropyl alchol in your tank don't use methyl hydrate it's not good for for aluminium engines.If it seems to clear up somewhat put a little more in and run it for awhile see what happens don't use more then a 3ounce bottle Good luck hope this helps
 
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