03 wr 450 carb question

the bike is an 03 wr450, mechanically stock. no engine mods and stock pipe. only mods are a Baja designs street legal kit.


took the carb to a Yamaha dealer to have them use the ultrasonic cleaner on it and have the guy who's owned multiple WR's re-jet it to make it work like our 07 w/ AIS removal.


the 07 is easer to start cold mornings and runs a fair bit cooler on tight trails. figured it was lean jetting like one reads all over the internet.


phoned them today and it's ready, the tech there said that the carb did have some gunk in it, and the stock jetting should be fine for a stock bike?????   I've read all over the place about these things being wrong from the factory.


I'm not convinced that cleaning was enough... is it possible for a somewhat gunked up carb to cause a certain amount of a lean condition and cause these symptoms? so cleaning it and engine ice should help it out a lot? or does this tech not know his stuff?


the bike runs great and had a few hundred miles on this year since we bought er'. just gets real hot on tight trails (feels stupid hot on legs but never reached boil-over) and is a real pain to get going on a cold morning and needs a ton of choke before it'll idle cold no matter the outside temp; where the 07 isn't much warmer then my old TT-R 225 in the tight trails and fires up pretty easy no matter the temp and only needs a few seconds of choke.


we bought both bikes the way they are now but the 03 did sit around for a little while and the owner of the 07 seemed like a pretty serious rider who took good care of stuff.  so I believe there being some crap in the carb of the 03 but research shows they all needed different jetting.


thanks in advance just trying to arm myself with the info for when I go pick this up and talk to this tech in person.

Edited by essonlaker

Stock jetting is fine for a stock bike. It is a wives tale that 'that factory jets them all lean'. Really ridiculous if you take a moment and think about it. Why would a manufacturer sell something they know does not work right, deliberately. You change/adjust jetting if the bike does not run right. Fuel is not a coolant.


Hot has little to nothing to do with jetting. More to do with the speed (airflow) and the bike gearing/rpm/clutch slipping by the rider.


There is no such thing as 'magic coolant' either. Fresh coolant, coolant with a higher boiling point. You may want to ensure teh radiator cap is good and consider getting a slightly higher pressure one (raises the boil over point). Perhaps too, a change in final drive gearing may help.

okay thanks I will see how it runs, it seemed strange they would sell something that's not right, I figured they may have been some myth to the concept. the 03 bike is just as good power wise as the 07 so i'd call it running right. I know lean will run hot but maybe it was just gunked up, but clean enough to run ok.


I try to hurry on tight trails for the sake of airflow. the gearing is stock and I keep the revs low when possible, and the trails I ride aren't that ridiculous, clutch is either in our out. sometimes lots of shifting but no feathering/ slipping.


im going to use the engine ice because it cant hurt because at the very least its a coolant change. and has a high boiling point. the bike has never boiled over. it is just a hell of lot hotter then the 07. if I can tell by feel on my legs its way hotter, then its too hot. 

Edited by essonlaker

got my carb back in. our garage was about 60* and the bike only needed a few seconds of choke, thought it was pretty good  since she hasn't run since November. and runs at least as good as ever, probably a bit better. stalled once right after it went out in the cold but another shot of choke and it was fine. went for a tear down our road, hope the neighbors loved it as much as I did.  



it never got boiled over last summer, just hotter then the other bike so we will change the coolant and see how it is next year. good to know that my local dealer does good work as well.

essonlaker: How warm is the climate where you ride? One thing I know from my '06 (last year with a carb) is that it is more sensative to temp changes than any other bike I have. In 80 90 degree weather fine. A little stubborn all around when its 50 or 60 deg outside. Very finicky when it comes to outside ambient temperature is my experience


I live in new england and in the summer time it seems to run hot. I am looking into jetting it a bit fatter in case it is running a bit lean (yes, lean will make a bike run hot). I have no idea how the guys deal with this bike in a hot climate like the south west. One thing I have notices is a higher flow water pump by Boyssen (the reed guys). I bet that would help alot. Others take computer fans and put them in the radiators. I think its safe to say this bike runs hot


All this said, sounds like your main prob is with cold starting so I'd confine any rejetting work to the choke circuit. Typiclly, in years past the factory favored the rich side to avoid warranty claims with blown engines although they also have to meet EPA requirements today so I dont know what to say. look at plug first and see if you are running majorly lean or rich to begin with though.

last year with a carb? our 07 is carb'd? maybe FI came out partway through the year. anyways, I've ridden slick muddy trails including some 1st gear crawling type stuff in the summer with temp in the 80's without it boiling at all so i guess its not THAT hot. the bike starts better so im assuming dirty carb wasn't helping as far as lean



mine just took a ton of choke before it'd idle, like a couple minutes at least. it started easier in the 60 degree garage after reinstalling carb then it did in 80 degrees this summer, and i was able to start it without getting the starter hot the next morning at about 40 degrees so much better that way.  so that carb was indeed dirty as the dealer tech said. he ran it through an ultrasonic cleaner, verified the jets were stock and made sure float height was set right. and it started better.


the plug looked great, it got a new one (tank was off already) NGK CR8EIX, iridium version of factory plug, and what was in it already. 

Carb till 2011

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