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TR250 misfire

Our 1968 TR250 misfires and the points are dirty again after about 50 km. Any ideas?

When did you last replace the condensor?

Dirty meaning, burned and pitted? Yes, the condenser.
Dirty meaning, dusty? And the gap is closing up. Check to see if the point cam is pitted. A little point lube wouldn’t hurt.
Dirty meaning oily? The oil seal(s) might be on their way out.

Pitted points can be due to improper gap of the points or the condenser. It can also be caused by using the wrong coil.

If it says Lucas on it, then dirty, pitted and mis-firing is NORMAL…

MANY owners of vintage motorcycles replaced their stock coils with a far more robust automotive coil. That’s fine, but you must replace the CONDENSER to one that matches the new coil…It’s called impedance matching, the coil and condenser must balance each other to avoid arcing at the points…If the coil tends to run quite hot, then you need a dropping resister too…Is the bike 6 or 12 volt?..

The TR250 is a small volume car model, a TR-5 without the fuel injection. More here:

1968…I assumed it was a motorcycle…Not much difference in the diagnosis though…