Worn out battery...

[His Dudeness]

An update:

I Araldited a sheet of tough plastic onto the side that was showing signs of electrolyte seepage and the battery still squeezed into the bike OK.
The bike has been running poorly for a while… lots of misfiring below 5000 rpm, so as a fix I swapped in a clean set of carbs. After 3 on-off cycles of the ignition the float bowls were filled, but pressing the starter button did nothing. After a few more tries the starter relay got the idea and clicked… after a dozen more tries the contacts managed to clean themselves and the starter motor churned the engine over. Another 20 seconds and it fired up. 
First time it’s run since November… not bad for a battery that by rights should be knackered. 
Unfortunately, the misfire is only slightly better. Maybe some fresh petrol will help, but swapping the engine is the next step... no 2nd gear is such a PITA.

Have you still got the original spark plug caps? A new set of NGK caps and trim the ht lead might cure the misfire under 5k