Two Stroke Motocross Forum > Technical

CR 85 loses spark

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Ribs:
I've got a spark issue on my 2005 Cr 85rb, here is my problem--the bike runs great then all of a sudden it will stop running(no spark) if I let it sit for 10-20 minutes it will start and run just fine,it does not do this all the time ,it's only happened twice in the last 2 months, is the coil or something overheating..?

Stusmoke:
Does it consistently do it after 10-20 minutes or is it fine some days? What sound does it make when it dies?

Ribs:
It sounds like it is running out of fuel,but it is not the fuel if I pull out the plug there is no spark,if I let it sit for 10-20 minutes the spark will magicaly start working.the bike will run great for days,sometimes weeks.ive gone through all the wiring no loose connections that I can find..

eprovenzano:
I'm working through a similar issue on an old XR100 I'm rebuilding for a friend...  Test all electrical components when the bike is cold...   (Google how to test the electrical components.)  Test the coil, stator output, and output through the CDI, and write down the results.  Take a heat gun / blow dryer and heat up each component, and retest.  Hopefully you will find the the one that's failing. 

rlaj1004:
Sounds most definitely heat related. You probably already know this but heat increases resistance, resistance can fault a component or wiring to the point that you lose spark. Have you noticed does it do it quicker on hotter days.

You can improvise on testing procedure eprov recommended. Make sure the bike starts, has spark. Pick a component, heat it up, fire the bike up, turn it off, move to the next one.....
I friggen hate going through electrical test procedures personally.

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