Gn250 running problems

[jake47]

Hi been a while since ive been here but being a brit where there aint many gn250s i can come here and ask you wisened kiwis for your help.
Btw i upgraded the above to a 300cc with a piston upgrade(chinese)over 18 months ago and til recently its been running real good.Right here we go over the winter i started the bike up every few days and it always ticked over great ,now this summer i was away for a few weeks and i came home pressed the button and it turned over but didnt want to start,bugger that ,checked the spark it was a bit weak so i put on a new coil, not much better but it started but would only run with me giving it plenty of revs on the throttle when i backed off it died.Thought maybe carb was the problem as the choke seemed loose and didnt seem to do much,cleaned the carb and it was no better.So i got a second hand carb wacked that on and it fired up straight away ticked over nicely at about 1200rpm ,gave it a whirl took it upto 70mph and ran it around for 40 mins or so ,power was fine acceleration was as good as it had been at its best(ok its a gn so not brill lol however)came home and at a standstill choke was off it died,tried to start it ,no way turned over but didnt want to start,so i left it to cool then hey presto an hour later when cool it fired up sweetly and ticked over ,i though what the hell is going on here.Now ime no mechanic and cant afford these bloody garages who charge an arm and a leg,so ime not sure where to go.Could it be something to do with the igniter that bloody little black box,i did check it out with a meter on it and it didnt fall into the tolerances shown in the manual,so what do you think/As i say when hot it dies and doesnt want to start any ideas you kiwis, please.HELP.

[Linz22]

This should not be as frustrating a problem as it appears - and sounds very similar to problems I continually have with my GN after left standing.
You put a new carb on it and the problem was immediately solved. So that's where the problem lies, not with the CDI nor anything else electric.
That the new carb was a temporary solution suggests a blockage caused, almost certainly, by dirty fuel. Check the filter at the petrol tap, then the in carb filter, float level and jets - blow them through with an airline...
BTW, if you still have the other carb, I could do with a spare. Let me know what year it is.