Main beam surge

[brucewayne]

So if I'm riding along and put main beam on and it decreases the engine slightly,
would that be alternator or buggered battery?

 

[Colban]

Probably nothing to worry about.How old is the battery?.
Does the bike start from cold OK?.Any hesitation/ABS lights stay on?.
Easy to check alternator belt tension.Any signs of slipping?.
Check charging voltage across battery.Should be about 13.6V ish with engine running.
Check leads for grot and tightness.

 

[brucewayne]

Battery history is not know, bought bike 4 mths ago and have been doing it up (off road) for 3mths so battery not used. Took 2 nights of trickle charge ok and starts fine with no ABS probs, so seems to hold charge.

Will have to get me multimeter out and learn how to use it too!

 

[motobiker]

I've always found the most reliable test of the battery is the abs... failure to set properly always seems to be the first symptom of a bad battery.

 

[PIGGLET]

I've never noticed main beam causing a noticeable reduction in power while riding, even when I had FF50's wired into main

It's slightly noticeable when the bike is stationary at tickover and you switch the lights on but not on the move for me. Have you checked how much current main beam is pulling? Is the wiring to the bulb hot?
Or are you just super sensitive

 

[brucewayne]

Or are you just super sensitive

Will ask the wife

 

[buellzebub]

I say it's probably normal. As the drain on the battery increases, the current output from the alternator increases, this in turn raises the electro-magnetic resistance in the windings which takes more effort from the engine to turn; hence the drop in engine speed.
hth,
Mick