newbie

Hey all, bit of a clueless newbie here :worthy:

(many) years ago i used to ride 2 stroke mx and then had a long stint on sports bikes. I've just sold it and bought my first 4 banger (04 yz450) with lights and plate to do some trail/woods riding, enduro and maybe a few mx tracks (i'm not exactly track fit).

The problem is when i started it from cold (at night about 5c outside) it started to dump the coolant after about a minute at the most!! I've read on here that they overheat quite quickly but a minute from stone cold...is that normal?

If you're talking about sitting and idling, yes, it's normal. They can begin to push coolant out in as little as two minutes that way keeping the revs up seems to help a little.

Since it's a used bike you may want to check the condition of the cap and the coolant, both of which will contribute to early boilover if they get weak. Have the cap tested, and probably just replace the coolant.

And its also important not to over-fill the radiator. The coolant level just needs to be over the core. If you put much more in it, it will puke it out rather quickly.

cheers fellas, thought i'd bought a dud :worthy:

If i could just pick your brains again until i get to grips with this thing. Unbelievably it starts first kick when cold but after 30 secs when i try to pull away it dies unless i very gently build the revs and slip the clutch. Also when it's hot it's a pig to start, the revs hang a bit high when it should be idling and it pops like a machine gun every time i chop the throttle.

I've done a bit of searching on here and i'm guessing it's running too lean and needs a jet change? Is there a way i can tell what i've got in there as it's all a learning curve for me (although i'm not shy mechanically and have no quarms pulling it apart).

That said it pulls like a train and gave me a bigger grin than i've had with any sports bike when i opened her up on a single track for the first time :worthy:

I've just ordered a FMF Q4 to quieten it down before i get an ASBO for riding it through my village to the woods (road registered). Could this pipe make it run a bit richer and maybe solve the problem?

check the plate on the carb slide.It should be flat side down. I worked on a bike with the same problem and that's all it was.

...it starts first kick when cold but after 30 secs when i try to pull away it dies unless i very gently build the revs and slip the clutch. Also when it's hot it's a pig to start, the revs hang a bit high when it should be idling and it pops like a machine gun every time i chop the throttle.

I've done a bit of searching on here and i'm guessing it's running too lean and needs a jet change?

I wouldn't concern myself with the throttle plate. If that's reversed, the bike would be extremely rich off of idle at less than 3/4 throttle. It could have cracked off a corner of it, but that's pretty rare in '01 and later models.

You probably need to adjust the pilot screw. Your symptoms indicate a leab idle circuit. Read:

http://www.thumperfaq.com/jetting.htm#PJ

Then:

http://www.thumpertalk.com/forum/showthread.php?p=3710599#post3710599

and:

http://www.thumpertalk.com/forum/showthread.php?p=3350613#post3350613

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