Vintage Dirt Bike Q & A

Hi all, have just finished rebuilding/restoring an MT 250 in the style of a CR250M . Both models are rare beasts here in England . Its been a long slog in between racing and restoring a couple TZ Yams.

Finally reached the point of firing up my little silver and green beauty this evening.Five kicks and nothing Wet plug and good spark indicated that the timing needed resetting.When I checked it,it was trying to fire at appoximately 35 -40 degrees BTDC. Way too avanced!
The really strange thing was that there was just too little movement in the stator to allow it to be retarded off anywhere like enough.

Whilst taking time out to ponder the problem I realised what might have happened..... I had rebuilt the motor from 2 very rough ones to produce 1 good one. Had I inadvertantly mixed the rotors and stators? I rumaged around and found the "spare " ignition. I simply swapped out the fitted rotor for the "spare" one and.... HEY PRESTO I had myself one sweetly runing Elsinore on the first kick

I really wouldn't have believed that Honda would have produced ignition components that were partially/completely non-interchageable. I have thought about this an wonder if my motors were different years. I will check this out tomorrow and let you know what I find. Hope this little story saves somebody a bit of grief.

Mark.

Well, I've checked out my engine numbers.The engine in the bike starts 200_ _ _ _ and the spare engine starts 100_ _ _ _ I believe this makes them 1976 and 1975 respectively. I really thought that there were no differences between these years. Perhaps somebody will be able to tell me differently?
Mark.

A way to double check is to go to a place that has a parts list on CD and double check the part numbers for different years. My Haynes manual doesn't show any difference between models but it isn't exactly an exhaustive source.

Rick

I checked my source material and the engine serial beginning with 1000 is a 1974 MT250KO.
The 2000 serial is a 1975 MT250K1 and 3000 serial is a 1976 MT250.

The ignition components have the same parts numbers for all three years and are completely
interchangeable.

Just a guess, but maybe that first rotor/ignition you tried wasn't OE on that "rough" engine.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

Is the MT like the MR, where the only timing change you can really make is by adjusting point gap??

That is certainly the case for the MT250. Certainly makes ignition timing a doddle to set......unless like me you mix rotors!

Mark.