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This information was given to me by a giifted young Mechanic from QLD whom diagnosed my bikes issues across the internet, so full credit goes to him..Onya BO
Does your YZ idle erratically?
Does it stop for no reason at times?
Does it seem to “break down” and stutter at higher RPMs?If you answer yes to any of these please consider the following
as the coil and associated hardware get a bit of age on them they start to loose a bit of insulation, this is not normally an issue except if you have an ECU, CDI or the likes nearby, mine was stopping inexplicably at low revs, and occassionally stuttering at high revs, I replaced jets, cleaned the carb 4 times down to bare body, redid the float dozens of times, checked needle & seat with a magnifying glass, checked the floats and stop tangs, rerouted the hosing, fuel tap & filter, kill switch you name it……….until I asked young Bo.
His response was that he has had a few in with the same problem, the first took two weeks a handful of mechanics and a lot of headscratching… finally he nailed the problem with an oscilloscope and discovered the CDI going nuts and then his genius brain deducted the rest. Now he has had to rewire quite a few “99-’05 model Yz250s to relocate the CDI up onto the headstem away from underneath the Coil where Yamaha in all their wisdom had changed them to. This had cured all matter of ills such as mine, in the later models yamaha has returned to mounting them on the steering head again, possibly for this very reason. On my particular bike this is not an option as I have all the WR electrics behind my headlight (’03 YZ250WR) and there is no room, so I rewired mine into the airbox area, not the prettiest wiring loom now, but secure and tucked up out of the way and even better the bike has a stronger idle with a constant “Ding DING, Ding, DING, rather than a “domp DING domp DING” and doesn’t seem to have the intermitent stutter at revs anymore.
So my hats off to the man who gave me the heads up on this as I would never have worked it out myself, probably would have torn the engine down first.Mr Blue
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