My carbi is a mess wheres a good starting point of tuneing

Well my story is a long one lol here it is

A few months ago brought this bike 03 WR250F it had a slight miss when i brought it i fugured that i would be able to tune it out (WRONG). After makeing the mix richer it would be ok, 3 weeks down the track it would be missng and craping on again. This happend a few times and i started to think this is really not correct, so i explored a bit further and found the valves wer absoluly stuffed out.

I just finished rebuilding the head everything is to spec i have checked 5 times, the drama now is, it is now missing and coughing more than ever. I am now looking at the carbi , the carbi is a mess. due to me trying to tune the untunable

this is what i have

03 wr250f

full staintune system

stage1 YZ250F hot cams

stainless valves

high rev valve springs


Main jet: 180

Pilot Jet: 45

Fuel screw (turns out): 2

Needle model/Clip position: OBEKR 4th

leak jet: 90 ( only getting .26sec of AP squirt duration)

Temp: 15~40 degrees

Altitude where i ride:0~1500 feet

Spark plug: is balck and sooty,the porcalin is a really dark brown neally black

i dont even know if wats happening is the carbies fult

any advice is good advice

cheers to all

Jetting looks pretty good. Could try the clip on position 3 from the flat/top. Unless all you ride is fast MX, you might want to try a smaller leak jet, perhaps even a 40 or 45.

Did you try a fresh plug?

Did you confirm all electrical connections are sound and no wires are chafed?

yes new plug

the wireing is a mess, so i will strip it down and start that from scatch i think

Good man.

Best to ensure everything is right before you waste time chasing your tail!

unplug the tps before doing any more jetting.

is $312 AU the correct price for a TPS

As Eddie suggested, is it better with the TPS unplugged? If so, fif you check the radings from it with a meter?

unpluging the TPS made no diferance i also pulled out the multi meter and all TPS readings are in spec

also a funny update

I jumped on yesterday whent down the road and it was running supreme. I pulled the front wheel up in the air, and the split second the front wheel touched the ground (with a bit of head shake) it started missing realy bad again , so i started comeing straight home, just around the corner form my house it died in the ass and would not go, i got it home pulled the tank off litualy touched a couple of wires and it fired up againe but with the MISS still present.

I whent through all the wireing this arvo, I tieded up wat i could and did not find any dramas , i didnt put the multi meter on any of the diodes or watever though ( i dont now which one do wat yet lol). after all this there was no diferance.

NOTE miss is after 1/4 throtel

would i be advised to post this in a diferant forum lol


Read your shop manual, test the ignition pulser (spark timing sensor) and source coils.

Read your shop manual, test the ignition pulser (spark timing sensor) and source coils.

can do cheers buddy

Read your shop manual, test the ignition pulser (spark timing sensor) and source coils.

looked through the manual and searched around abit , i have not found much info on either of these specificaly is there diferant names for these

LOL, yes, Yamaha named them the pickup coil and signal coil.

I have a feeling your issue is with the pickup coil. Typically, as these get ready to fail, the problem manifests itself as a high rpm miss first.

pick up coil is in spec reading :287 ohms resistance

Ac magneto im not sure i am borrowing a better multi meter with more decimal places tomorow night

William my father told me to hold the ignition coil inslator beside the head and wind it over, sparks came out the insulator with no spark plug in, so i put a spark plug in and it would spark across to the head , but when i slowly moved the spark plug away from the head it would then spark out the insulator again. (By insulator i mean the plastic shaft (the mid section) )

If this means its stuffed then alot could be answerd for , except the question "why did it run great all day monday until i puled the when up in the air "

Do you have any thoughts on this

I will test the AC magneto in a couple of hours after work

really really apreciate all this help


just thought i would let you guys know , i took it to a good bike shop and 3 weeks later they tell me its the CDI and they have tested a new one in it ,

So thankyou verry much for your helps

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