Low beam on engine dies

[bikemonkey]

Haven't tried high beam yet, but on the way to work earlier I started with sidelights on then switched to low beams on the move and the bike mis-fired.

Will take it for a little run after work and investigate some more.

[magg]

If high beam gives you a similar engine running problem I would start by checking the charging system. Ensure you have 14-15 volts at the battery at 5000 rpm and also load testing battery.

[bikemonkey]

Small update on this, bike checked out fine after I fitted the new relay, worked well.

But earlier when I set off for work it was back to its old tricks. Bike died when I flicked the light switch, cutting the engine and lights. Yet when I got to work it all worked perfectly.

[magg]

Sounds like the battery is not getting sufficient charge or is stuffed, and after start-up has insufficient stored energy to support the load of the headlights until the charging system has been running for a while, like by the time you have arrived at work.

Suggest you check the battery voltage after start-up and after turning on the headlights. Should get 13-14 volts at idle after a few minutes engine running, no lights. Any less suggests a dud charging system. Lights on should require approx. 2500 rpm to get 14-15 volts at the battery.

[bikemonkey]

Hmm battery is brand new, and cranks hard even after the engines been cut by the lights.

I'll get those tests done tomorrow, but I can't see it being the charging system as its fully sorted. Or at least I think it is.

[bikemonkey]

Hmm funny thing is I stopped off at my mums after work for a few hours and getting back on the bike to go home it behaved perfectly, flicked lights on just before I reduced the choke (like normal) and it didn't cut out or anything.

I'm beginning to think its an intermittent short, but I'll still check everything tomorrow.

[magg]

Problem may not be an intermittent short, could be an intermittent fluctuation of electrical power. Do any other electrical bits perform poorly when the engine begins to run rough i.e. headlights (both hi or lo beam), running lights, turn indicator etc flicker.

All fuses making good contact, including the main fuse in the starter relay. If battery voltage is stable when the problem occurs try measuring the voltage at the black/white wire on either ignition coil when the problem occurs. This wire is the 12 volt feed from the battery to the ignition control unit and should also remain stable at all times.