Hello everyone, Boo here.
Today's story is about the regulator failing on my XR250 BAJA.
One October, at about 6 pm (around 18°C, I think), the engine speed stopped matching the throttle.
When I opened the throttle the bike lost power (misfired), but if I held the throttle at a certain opening it ran at a steady speed.
That day, I nursed the bike home by holding the throttle slightly open at a steady speed.
After that, the symptom came back now and then (some days the bike ran with no problem at all), so I suspected the carburettor (fuel supply) and left it, thinking "I'll clean the carb in the winter".
But one day, about 40 km from home, the engine suddenly stopped.
After that, nothing would get it started again.
This was the situation.
- The kick-starter went down
- The starter motor turned
- There was a nasty, acrid burning smell
- There was still fuel in the tank
So I suspected an electrical fault and checked the fuses, but none had blown.
It was getting dark, so I left the bike at a friend's house nearby and somehow got home.
Later, when I took my time checking the bike, I found the burning smell was coming from around the regulator.
I took the seat off and found that the resin (or silicone?) part of the regulator had melted, and that was where the smell was coming from.
So I replaced the regulator, and the engine started and ran as if nothing had happened.
From this I concluded that the regulator was the cause.
I think what happened was: the regulator was faulty, so as the engine revs rose it couldn't regulate the voltage properly, which caused misfiring and loss of power.
Until I replaced it, I wasn't confident the regulator was the cause, so I fitted a cheap one (about 2,000 yen). Seven years on, that regulator is still working.
Still, it worries me, so I now carry a spare MOSFET regulator with my on-board tools (it was cheap, so it may not actually be MOSFET inside...).
Since then I've also fitted a cooling fan to the regulator and carry a spare: