Coil Insulation Leaking Spark

3 replies to this topic
  • ACM

Posted February 28, 2013 - 12:17 AM


My 2009 YZ450 engine has come back from a rebuild, but will not start.

I've cleaned the carb, and put in an iridium plug, but still no joy. On kicking it isn't completely dead, but never takes at all. It has some backfires, but never anywhere near starting. I tried tow starting it, and nothing at all (worse than kickstart - I'd guess it just became flooded).

I have a question on the coil.

What I did:
To check the spark, and generally draw things through, I took the plug out and pushed it down the road with the coil laying across the top of the frame with the plug in.

The spark was great. Even with the end of the plug held back from the frame slightly, it was jumping at least 1/4 of an inch between the plug and the frame, no problem.
However, when I laid the coil across the top of the frame, with the plug not earthed, at some positions a spark could be seen coming out of the coil itself, about half way up the tube, into the frame.

Is this normal, or does it indicate some kind of failed coil insulation that will be leaking HT when installed in the bike?


  • grayracer513

Posted February 28, 2013 - 07:05 AM


Sounds like the coil is cracked. Replace it.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • ACM

Posted February 28, 2013 - 07:13 AM


Thanks for advice!

  • ACM

Posted March 05, 2013 - 08:47 AM


Having real trouble sourcing a replacement coil locally (Riyadh / Abu Dhabi). Looked into getting one shipped and looks like it will take weeks.
So... Thinking about trying to repair it. Even just to confirm it will start, so I know it's not something else.

Having taken the rubber end off, there is a small crack (see attached)

Would epoxy glue be a good enough insulator?
- Any other ideas?


Related Content


Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

05 yz450f not fast enough by RedeyeYZ

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.