03 Yz450 Exhaust/pipe/fuel issues

I live in Michigan and have a 03YZ450 I bought in 2005 from a guy who only rode it in few times. The bike is all stock. I have ridden it one season (2005) and it seemed to run great. All my riding is single track stuff. The bike seemed to have a cold. When in neutral and I gave it gas it would kick out black smoke. I took the muffler apart and the packing was solid black. The plug was black and loaded up. I repacked it and cleaned the spark arrestor, air filter and put a new plug in it. The tail pipe itself was loaded with black carbon, so I cleaned the head pipe and exhaust out too. Before I did all this, the gas mileage I was getting when I first got the bike to now is decreased substantially. When starting hot I would have to give it full throttle to start it, but it would start with one kick. I haven't ridden it yet but I am wondering if it could need the valves checked? If the values were off would it cause the gas mileage to decrease? My first thought is no I just need to adjust the air/fuel mixture screw and give it a try. Anyone one have similar issue or suggestions? : Confused:

Sounds like your very rich. Did you happen to buy and ride it when it was 20 Deg outside? J/K I'm no expert but my 03 is very finicky with jetting. 10 Deg change in temp is an 1/8 to 1/4 either way.

It once ran great now very rich :thumbsup:


Thanks for the response. I have been running this summer. The temps have been about 40 to 90 degrees. It does run better when it cooler out, but that is usually the case with all the bikes I have had.

Check the jetting - sounds way off on the rich side -

Go back to stock - and start over

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