2003 YZ450 hard to start

9 replies to this topic
  • egsmith2

Posted January 12, 2009 - 07:18 AM


Hey guys, I've searched the forum at length and can't seem to find the help I need. I have a 2003 YZ450F that I just got back from a local shop. I originally took it in because I tried messing with the fuel screw as it seemed to have a high, hanging idle. It still ran fairly strong, but just wouldn't idle. After adjusting the fuel screw in and out, and then back to the original position, it had no power and also bogged off of idle. I took the carb off, attempted to clean the jets and everything, and also replaced the spark plug. When I put everything back on, it wouldn't start at all :thumbsup:. It would backfire occasionally, but never run. The guy at the shop said that he adjusted the valves, cleaned the carb again, and checked the compression. He also said that when he kept it in the shop overnight where it was warm, it would fire up pretty quickly, but when it's kept in the cold (where I keep it), it takes forever to start. His response is that it's just a really "cold-natured" bike. I'm not willing to believe that because I never had this trouble last winter, used to start in 3 or 4 kicks, no matter how cold it was. Also, when I do FINALLY get it started now, it seems to not have the power that it did before. It runs alot smoother now than it did before when I'm on the throttle, but it seems to back fire alot on deceleration. Any suggestions before I think about taking to another shop? Thanks everybody.

  • work sux

Posted January 15, 2009 - 10:20 PM


Sum 1 help the poor bloke

  • egsmith2

Posted January 16, 2009 - 06:59 AM


Ok, looks like from the "similar threads" at the bottom of the page, I might try adjusting my fuel screw again, then looking at my jet sizes. Do bike shops normally sell individual jets? Which one is the starter jet, and which one is the pilot-circuit jet?

  • Ogener

Posted January 16, 2009 - 09:21 AM


Someone correct me if I'm wrong but excessive popping on decel usually means a lean condition. If that Is the case, you may need to richen your jet sizes a notch or two to correct the lean and to help the bike run better in the cold. If it gets cold there like it does here in Iowa rejetting is needed in winter when the temps get near freezing to get the bike to run properly.

  • egsmith2

Posted January 16, 2009 - 09:55 AM


The temps here range from 35-55 in the wintertime. So I figure I need to richen up the jets to get it to run. I'll try richening the fuel screw to see what kind of results I get, then I'll move on to the jets.

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  • toner

Posted January 16, 2009 - 10:04 AM


how are you doing,toner here tell me this did the bike run and start ok before /all it had was a high idle,

  • egsmith2

Posted January 16, 2009 - 10:10 AM


Thanks Toner, before the high idle it ran super strong, and seemed like it was pretty smooth. It revved quick and didn't bog. The high idle seemed to come around when the weather started getting cooler.

  • grayracer513

Posted January 16, 2009 - 10:54 AM


The high idle seemed to come around when the weather started getting cooler.

That sounds like the weather pushed it lean. If you ride a lot in very cold weather, you may also want to bump the starter jet up a size or two in addition to the pilot and main.

  • egsmith2

Posted January 17, 2009 - 07:28 AM


Thanks everybody. It's WAAAY too cold to think about working on the bike right now, but I'll try out your suggestions once it warms up. Ahhhh, wouldn't it be nice to have a heated garage....

  • BC3

Posted January 17, 2009 - 09:45 AM


[COLOR="Blue"]I also have a 03 450F I was having trouble with the compression just going away for no apparent reason? I heard about a product called "Sea Foam" which removes carbon build up on valves and piston tops....Thinking that the valves were not sealing from carbon build-up.
I went to my auto parts store and they knew what I was talking about and sold me a can.....I read the instructions and was totally blown away at how good my bike started and ran after the treatment. Not saying you will get the same results but it's cheap and I think by now your 03 is probably suffering from the same deal...Try it out and get back to us... [/COLOR]

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