Random sparking from spark plug

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kevingkruse

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I have tried searching around for this problem but couldn't find anything to help, sorry if I missed a thread that contains my problem somewhere. My bike was working fine until one day I was pressing my killswitch randomly to make it backfire (I think it sounds funny :p, but probly not good for it?), then it wouldn't fire anymore. I would try to start it back up but would only backfire once or twice without starting. I thought maybe I blew my head gasket cas it was making that high squeaky noise so I replaced it, fixed the squeak but still backfires and doesn't start. So i thought it wasn't getting a spark, so I unscrewed the spark plug and turned the wheel while holsing the plug and it seems to only randomly shock me instead of a consistant flow of sparks. I replaced the plug and still same thing. I looked at the plug after each try and its very slightly moist but not drenched. I wouldn't think the CDI or magneto is broken or else it wouldn't spark at all. I also unplugged my killswitch to see if it got stuck but still same thing. All other gaskets seem good, I'm stumped on this one. Any thoughts?
 
My spark was weak and intermittent when the engine was brand new. I bought a new CDI and magneto. The CDI was bad. I replaced it and that was it. Runs great. Now I have a spare magneto.
 
well...duhhhh. the spark plug is supposed to only spark "randomly"....like this : spark, no spark, spark, no spark, spark....etc.
There is a magnet on the magneto and the spark plug will only spark when that magnet is in a certain spot as the crankshaft rotates (this is called spark timing).
are you sure it's getting fuel?
 
motorpsycho said:
well...duhhhh. the spark plug is supposed to only spark "randomly"....like this : spark, no spark, spark, no spark, spark....etc.
There is a magnet on the magneto and the spark plug will only spark when that magnet is in a certain spot as the crankshaft rotates (this is called spark timing).
are you sure it's getting fuel?
Click to expand...


LOL good one...You may of sheared the woodruff key (in the magnet) when you backfired it. When the piston is a TDC (top dead center, all the way to the top of the cylinder) this is the proper magnet alignment. Notice where the cutaway for the key is located.
 
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theres also the boot of the plug itself. i find after a few hundred km or so that the little brass fitting inside shreds, leaves nice brass powder down the insulator, and the spark decides brass is far more appealing than attempting to jump the plugs gap!

usually signified by a strange popping "crack crack" sorta sound when starting.

when it gets wet (rain) i have to dry boot, plug and wire before i can start. once its warm, tis ok.

depending on how your killswitch is wired, you probably burnt out the magneto :)

cut the white wire off.
 
@motorpsycho
Well its not sparking every other rotation, more like every 10-20 rotations. And I'm sure the fuel is not an issue.

@Al.Fisherman
I removed the magnet and looked at the woodruff key, I'm not sure how to tell how if its sheared or not, it looks ok to me but I don't know. I also checked the alignment for TDC and its looks right.

@HeadSmess
I replaced the boot with an NGK and same problem. I had my killswitch wired green to black and yellow/red to blue. Would I just cut the white all the way to the coil solder?
 
a sheared key is obvious. if it pokes out above the crank by 2 or 3 mm then its fine.

have fun replacing the magnet (superglue the key in place or use a screwdriver and some determination)

yep. take the white off at the source! saves later frustrations.

so. it sounds like your magneto has fried.

multimeter, ohms...i think its around 300 or so between blue and black. anything majorly different = fried.

check the lil blob of solder up on the top front corner of the magneto coil. often the internal wire fuses right there and can be resoldered...
 
kevingkruse said:
@motorpsycho
Well its not sparking every other rotation, more like every 10-20 rotations. And I'm sure the fuel is not an issue.
Click to expand...

Sounds like the problem I had. I saw a few sparks, then nothing, then a few more. The engine wouldn't run but I got a backfire now and then. Bad CDI.

kevingkruse said:
@Al.Fisherman
I removed the magnet and looked at the woodruff key, I'm not sure how to tell how if its sheared or not, it looks ok to me but I don't know. I also checked the alignment for TDC and its looks right.
Click to expand...

Sheared means it's broken and cut in two. If it's one piece it's good.

kevingkruse said:
@HeadSmess
I replaced the boot with an NGK and same problem. I had my killswitch wired green to black and yellow/red to blue. Would I just cut the white all the way to the coil solder?
Click to expand...

Cut the white wire off at the coil or tape it and tuck it away. Don't use the white wire. Eliminate it so it doesn't cause a problem.

Can you afford some spare parts? A magneto coil, CDI and new spark plug are good to have in the tool bag when you ride any distance. My vote says if you replace the CDI you'll be happy. Get back and let us know.
 
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