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bewitched WR426F, jetting changes automagically

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2001 Euro model of a buddy of mine. ran fine,

fouled a couple of plugs until he got the idle

mixture right. when i bent my wr400f's shock

rod he loaned my his 426 for next day gravel pit

WFO hill climb extravaganza. all ponies very

alive and well, sweet throttle response.. :D

*a couple of weeks of neglect*

buddy and me drive to italy, break out the bikes

and his is a popping mess that won't pick up gas,

big, ugly hole when going from 1/4 throttle to

3/4 in a turn etc. :D

we ended up disabling the accelerator pump and

dropped the needle two notches => A#1 throttle response, no popping, first kick

starting, killer topend, super fine tricky

terrain throttle control blablabla. :D

*a couple of weeks of shed time*

he gets to a party and reports that he has to

have the choke on all the time, no idle and lotsa

hesitation w/o choke. :) Next day we set out for (last weekends) "riddle-ralley" so

instead of doing something ingenious we simple

take the carb apart, find all surfaces and jets

super shiny clean raise the needle back to center

clip and bike runs beautifully, again.

next day he stupidly fires her up for a minute

before setting up tent

Next morning, guess whose bike needs a fresh

plug. Furthermore turns out his 426 eats muuch

more gas than mine.

Later that day i decide to pass a rolling road

block going 90mph and buddy Nobs goes WFO too.

talk about killer acceleration..

but then...

all of a sudden right after the passing maneuver, his 426 is back in popping land,

banging the villages to kingdom come, loud enough

that Karin on the 1100GS can hear him detonating

while going +50 in the light drizzle. :D

The strange part is that vienna, Tuscany and the

Lower Austria area all are

- on similar elevation (within 1200 feet)

- the temps were at most 15°F apart

- my WR400F was around every time and ran

absolutely peerless w/o any adjusting


- his 426 is a low mileage bike, the carb to

cylinder head boot feels fine and looks

uncracked, carb slide is uncracked, too.

I'd have suggested he put the needle between the

.it and the stock pos, if it weren't for that

change in behavior after a short WFO section,

especially as we umm.. had an enormous WFO ball

on the twisty road catching up to our buddies BMW

and Transalp tankers after refueling w/o his bike

starting to pop again.

any clues how a bike can display such a Jekyll

and Hide personality?



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This plug fouling - mystery jetting has been posted before. The cure was a new carb if I remember correctly.

Consider swapping carbs with the trusty WR400 that runs good. If the problem follows the carb to the other bike that will confirm it.

Is the bike still under warranty???

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:) don't shock me like that! The carb as a spare is almost two grand without tax, over here!

Bike ain't under warranty anymore, so we'll try

that carb swapping test.

Anyhow, thanks for the suggestion


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