well the fuel should be alright, its the same mix that my mates gasgas is running and theres definately mix as its coloured, and had just filled up.
the bikes are stored in a mates workshop so you never use a random can, but we keep 3 5L cans mixed up for the trials bikes, though its probably nearer 50:1 as thats what the sticker says on the bike (noticed most people on here run 80:1)
from the rest of the suggestions,
the exhaust is slightly creased so could be a restriction, probably quite gummed up to as its mostly slow put putting about that the bike does
so will clean it and try and straighten it or drill an extra hole to make sure theres no restriction (new exhaust will have to wait)
ignition, i dont trust the stator, the bike can be a real pain to start when cold (fine warm) and ive always thought weak spark
so will probably get this rewound while the bikes in bits (not 100% sure if its needed but i dont trust it)
fuel starvation (running lean), will give the carb a good clean out and once over
whats the easiest way to set the carb, ie how do you tell if its rich or lean?
banjo - what do you mean by plug readings??
in general the plug has been pretty black, but only had it off to clean it when the bikes been reluctant to start (though the day it went bang it started really easy)
thanks for the input guys, the cylinders away to get replated so will be a couple of weeks untill i can get it back together