I need help! 2003 yz450f

3 replies to this topic
  • kcalb10

Posted January 28, 2014 - 03:34 PM


I just got a 2003 yz450f in a trade. Looks sick and that got me to do a bad thing. I traded a ktm for a yamaha. When the guy brought it he took it out and started it. Its the middle of winter only 10 degrees outaide. It took him a couple 6 kicks. I didn't think much of it because its cold outside. The next day I went out to start it. It fired after 3 kicks not to bad. But a couple days later I was showing it off to my friends by just letting it run. First kick it started to fire then just shut off. Since then can't get it going. We bump started it but it wouldn't run right and died low rpm. We cleaned the carb checked valves. I did a compression test. Only read 30psi! Then did a wet compression test it doubled to 60. I don't know what it could be. Please help and let me know what you think . Also the decompression lever isn't hooked up and there is a wire that is completly fraied going into the bottom of the motor. Please help!


Posted January 28, 2014 - 05:22 PM


I think the first thing I would do is pull the valve cover and check the timing chain marks.  Until you find the problem, I wouldn't start it.  If the chain has jumped a tooth or two, it is capable of jumping further and bending valves and or destroying the entire engine.


Not sure, but the frayed wire may be the wire that sends a signal to the ignition box, that let's it know that you're in neutral or first gear.


Maybe someone can chime in to verify about the frayed wire.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • nuity5

Posted January 28, 2014 - 05:44 PM


2003's shouldn't have a compression release lever - they have auto compression releases. I'm guessing you might be talking about the hot start lever. I'm guessing the wire you're talking about is the neutral switch as previously mentioned. Seems like I read on here all it does is set a different rpm limit for neutral. All it does is complete a circuit to ground when in neutral so it's not like it's shorted and keeping it from cranking. I didn't see a spec on cranking compression and I guess it would be pretty low with auto decompression. However as previously mentioned a quick look under the valve cover would be good. Did you change the plug? After a couple of cold starts without getting it hot it's a possibility and a cheap try. Clay

Edited by nuity5, January 28, 2014 - 05:47 PM.

  • Shadetreeyz

Posted January 30, 2014 - 05:28 PM


Mine did something of the sort o few weeks ago, Mine has always been a two kick start, after just riding it a few day prior I tried to start it and it would not start for the life of me, had to get a quad.. to pull me while dropped the clutch and still took dang near an eigth mile on pavement, I had to adjust my fuel screw because it had become somewhat loose, so 1 half turns out and then she fired up let it idle for a bit killed it and has started first kick every time. the hot start plunger on the carb itself and little boot can get stuck a bit open if you have messed with the carb by twisting it. The wire wont make a difference on starting. I agree with the above ost tho check the chain and marks make sure you dont mess up the valves.

Related Content

WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

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

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

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 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

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.