2008 yz450f SM conversion won't start

3 replies to this topic
  • ryanlee450er

Posted October 18, 2015 - 06:07 PM


I have a 2008 yz450f super moto NY street legal bike. The bike has some questionable electrical work/connections. I can't get it to start.I bought the bike fully converted about 3 years ago. I don't ride it very much. For the past couple years i've only taken it out a few times for few hours each time. I most recently tried starting it after it sat for about 4 months and it wouldn't run. So i started with draining the carb and gas from the tank and still wouldn't run with fresh gas. I then removed the carb and cleaned the jets and sprayed the carb out well with carb cleaner and compressed air. Reinstalled the carb and it still won't run. Then I checked for spark and it appears to be ok. I plan to get a new plug and try that. The bike ran fine when I last parked it and that's why I assumed it was just bad gas but the questonable electrical work has me concerned that something happened to a wire or connection. The bike has a key installed by the gas tank and no kill switch. I'm not sure where to go next. The bike has a battery custom installed in the air box that is suppose to charge and power the bikes lights although the lights have been very dim and the horn barely works pretty much since i've owned the bike. I'm not sure that would be related to the bike not running but figured it was worth mentioning. So who can tell me what I need to start looking into next to figure this out? Thank you for any help.

  • Krannie McKranface

Posted October 19, 2015 - 04:37 AM


Check for spark, check for fuel, check for compression


Were any of the carb parts noticably corroded?


Did you clear the passage above the pilot jet? It has a sharp bend the compressed air won't be enough

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted October 19, 2015 - 06:25 AM


More than likely the pilot jet itself.  The jet doesn't have to be clogged to the point where it's closed off, either.  If no more than a .001" film of varnish forms in the metering orifice, it will make a #45 pilot the same effective size as a #35; way too small to run.  


Read:  http://www.thumperta...o/#entry6879695

  • ryanlee450er

Posted December 03, 2015 - 06:35 PM


Thanks for the replies. I'm just seeing them now. I got the bike running and am not exactly sure what the problem was. I think it was bad gas bc I feel like the spark plug cap wasn't pressed all the way on causing the bike to not start after cleaning the carb. I did replace the plug though so either it was a bad plug or the cap wasn't firmly pressed on the last plug and or bad gas.

Related Content



Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  30 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
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 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.