2003 wr450 only runs with choke pulled

Hi I need some advice on my 2003 wr 450 It will only start if the choke is pulled fully out it coughs alot and misses and backfires when I hit the kill switch the exhaust gas is alot hotter than usual if I wind the idle up heaps it will run with the choke in but is idling very high and misses when I push against the choke grommet and choke housing the rpm seems to drop a little I am not very familiar with this bike as it is new. The bike has vortex ignition i fitted the stock unit to tshoot but no luck I dis connect the Tps but no luck any advice would ve appreciated

http://www.4strokes.com/tech/4sjetting.asp <for tuning; have you cleaned the carb ? is the fuel old ? valve's in spec ? do you have a leek between carb and head ? (a high idle cause)

Replace the pilot jet. Make sure the fuel screw is there, that the spring, washer and oring are in. Ensure the slide is not cracked.

the bike went in about 2 weeks ago and they replaced the neeldle and lapped the seat as t was allowing fuel to pass through the carby had a full clean and treatments i had an inline filter put in before the carby and i noticed there was a couple of rock fragments i pulled the top off the carby and moved the slide up and down and pullde off the bowl but it seemed clean the rubber around the carby to cylinder looks reasonable condition if you wind the idle right up it will start but runs rough i am still trying to familarize myself with the carby set-up could the choke be causing a problem? fuel is about 1 week old it just happened as i pulled up from a ride. the bike has about 3500 klms on it and has been well maintained i bought it off my brother-inlaw this is the first time it has ever had a problem but it did sit there for a few years with lack of use

also i had the valves done 200 klm ago the mechanic said they were well with-in limits.

+1 pilot jet. Classic symtoms.

the bike went in about 2 weeks ago and they replaced the neeldle and lapped the seat as t was allowing fuel to pass through the carby had a full clean and treatments i had an inline filter put in before the carby and i noticed there was a couple of rock fragments i pulled the top off the carby and moved the slide up and down and pullde off the bowl but it seemed clean the rubber around the carby to cylinder looks reasonable condition if you wind the idle right up it will start but runs rough i am still trying to familarize myself with the carby set-up could the choke be causing a problem? fuel is about 1 week old it just happened as i pulled up from a ride. the bike has about 3500 klms on it and has been well maintained i bought it off my brother-inlaw this is the first time it has ever had a problem but it did sit there for a few years with lack of use

You need to pull the slide from the top of the carb and check the flat plate that installs on the forward (toward cylinder) side of the slide to ensure the little hole is at the bottom, not the top. This piece is deceiving, as it looks like it should go in the other way, putting the hole at the top and will cause your bike to RUN EXACTLY AS YOU DESCRIBE. Ask me how I know this.....:thumbsup::busted:

i just pulled the pilot jet out i'l need to pick something up to clean it it does appear you can see a light through it and the pilot air screw is wound in full tight is this correct the bike has been running reasonably well about 200 klms without a drama since the carby was pulled and cleaned and new needle then suddenly she stopped and then i started to get the above problems

hey guys removed the pilot jet and replaced it with a new one it had a #50 without a speckle of light visible i swaped it with a mechanic he gave me a #48 and told me to wind the pilot screw out 1 3/4 turns out and :busted: it is running reasonably well but it is missing under constant rpm when i have the time i will pull the main jet and get it cleaned and maybe it will fix the problem

also the bike was getting the speed wobbles and the front wheel was washing out really bad as the ride progressed it seem to work a little better or i was getting use to it? if any one has any thoughts on how to fix this problem and a big thankyou to the people that responded to this thread all information helped me rectify my problem

regards mitch

Just a thought. I had a similar problem with my Hot Start cable sticking, the plunger wasn't closing fully. I chased the problem all over the carb first before I realised it was the Hot Start. The symptoms from memory were, the bike would start fine with full choke from cold but when warmed up and choke off - RPM high and exhaust/engine hotter than normal . Bike wouldn't start from hot unless using full choke again, Carb was near impossible to dial in to compensate to fault.

It's hard to gauge whether the Hot Start plunger is closing fully as you can't see in there, but probably a good idea to eliminate it by taking it out for a clean and lube the cable. I replaced the cable after a local MX shop told me it was quite common for these cables to shrink.

Worked for me, just an idea.

i just pulled the pilot jet out i'l need to pick something up to clean it it does appear you can see a light through it and the pilot air screw is wound in full tight is this correct the bike has been running reasonably well about 200 klms without a drama since the carby was pulled and cleaned and new needle then suddenly she stopped and then i started to get the above problems

guitar string works great to clean jets with. FYI

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