2003 WR450 weird running problem

Friends 2003 WR450F. I am a decent but no genius mechanic. I have a 2006WR and have been its mechanic...great bike.

2003 bike was stock when he bought it. (looked hardly ridden) Ran very poorly overall.

It has the stock carb, with new jetting mods by me (jetted for 4k altitude-basically mirrors my 06 WR, which is very good.) Float seems ok, i checked as best i could. Float bowl had a hairline crack where drain seats..fixed (JB weld) and not leaking. replaced accelerator pump diaphragm which was corroded (weird!). Put in a throttle stop (it did not have one...used my old stock one that is cut to 22mm). bike did NOT have the warranty mod on the flywheel. Had that done by untrustworthy local yammie shop recently. i did not check valves yet. stock pipe, with aftermarket tip (pretty quiet)...

Bike now starts GREAT, with or without button. 0-1/2 throttle..thing pulls fantastic! probably stronger than mine. .5-.7 throttle..pretty good, but sputters somewhat. .7-full throttle, thing sputs and sputters and is generally pissed off. Have been pulling my hair out with this. Tried removing exhaust tip..no difference. Tried disconnecting throttle sensor..no change. Tried different gas...nope. I tried other things i am not remembering i am sure....still nothing. New plug..no difference...grrrr

Drat! Yamaha shop is no help. It is as tho it is bad gas, or being starved for fuel (float?) at high rpm or ? perhaps i should check valves...(I adjust my own-easy as you know) bike is at friends house so i cannot get personal with it to find this darn problem...maybe i should borrow for a month.

Any thoughts or ideas are greatly appreciated. My (and many other friends) WRs really do run fantastic at all rpm, here, or on the top of the highest trails we ride 9000' + I personally think WRs are some of the best bikes out there, and would be THE best if they were not so darn heavy.

Thanks for any thoughts.

Friends 2003 WR450F. I am a decent but no genius mechanic. I have a 2006WR and have been its mechanic...great bike.

2003 bike was stock when he bought it. (looked hardly ridden) Ran very poorly overall.

It has the stock carb, with new jetting mods by me (jetted for 4k altitude-basically mirrors my 06 WR, which is very good.) Float seems ok, i checked as best i could. Float bowl had a hairline crack where drain seats..fixed (JB weld) and not leaking. replaced accelerator pump diaphragm which was corroded (weird!). Put in a throttle stop (it did not have one...used my old stock one that is cut to 22mm). bike did NOT have the warranty mod on the flywheel. Had that done by untrustworthy local yammie shop recently. i did not check valves yet. stock pipe, with aftermarket tip (pretty quiet)...

Bike now starts GREAT, with or without button. 0-1/2 throttle..thing pulls fantastic! probably stronger than mine. .5-.7 throttle..pretty good, but sputters somewhat. .7-full throttle, thing sputs and sputters and is generally pissed off. Have been pulling my hair out with this. Tried removing exhaust tip..no difference. Tried disconnecting throttle sensor..no change. Tried different gas...nope. I tried other things i am not remembering i am sure....still nothing. New plug..no difference...grrrr

Drat! Yamaha shop is no help. It is as tho it is bad gas, or being starved for fuel (float?) at high rpm or ? perhaps i should check valves...(I adjust my own-easy as you know) bike is at friends house so i cannot get personal with it to find this darn problem...maybe i should borrow for a month.

Any thoughts or ideas are greatly appreciated. My (and many other friends) WRs really do run fantastic at all rpm, here, or on the top of the highest trails we ride 9000' + I personally think WRs are some of the best bikes out there, and would be THE best if they were not so darn heavy.

Thanks for any thoughts.

sounds like it is running rich to me.

It wouldn't hurt a bit to start with fresh fuel though.

Do some runs at the RPM range where it is having issues and look at the plug.

1/2 to full throttle are effected mostly by 2 things needle clips settings and main jet.

Sounds like you have the correct pilot jet and the AP is working, as it starts easy and idles well.

Just because jetting works in your 06 doesn't mean it will work in your 03.

I would look through the jetting D-base for 03's that run in the same altitude and temp range. (use the search feature to narrow things down)

Make sure the hot start is not partially engaged.

we worked hard on the hot start, it seems to be seating...hot start threads had disintegrated, so replaced and cleaned and cleaned carb many many times so think it is clear...

thought choke..no..it seems to be seating too...i still wonder tho

adjusted accelerator pump per manual...no effect

i have yet ANOTHER friend that has a 03 that runs well with the jetting we have. agree with the notes tho. he is running, (from memory) a 48 pilot and 165 main, stock needle i think, as it has no marks on it but IS adjustable and in second to last groove. we are at 4k feet.

thanks for thoughts!

if the other 03 was in town, would love to swap carbs. i just feel it has to be the carb somehow

Another thing you could check is the flat plate on the slide in the carb.

Sometimes these get put in upside down, flat side goes down.

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