Richard get yourself a temperature indicator fitted like I did!
When io went out on the 2 stroke weekend a couple of weeks ago we ended up on a bloody dual carriageway and yes bit by bit I saw the temperature rise to an all time high of 264C...I wasnt too pleased but pt didnt heat seize and at least it makes you aware of whats going on
as far as jetting goes I would do this
First oil your filter well...I use 120 viscosity oil on mine I'm not keen on using thin oil here!
Find a main jet thats too big and runs rough on full throttle, then fit whichever smaller one stops the rough (4 stroking) running
once this is done do the same with the needle clip position, ie clip to the lowest clip position (highest needle posn) that it will run sweet with
check your ignition timing is bang on and if you find it is then dont be afraid of setting it a bit more retarded...ie 1.5 mm BTDC
Rub marks on the piston either side of the pin are classic heat seize
Have you ever done any jetting tests and set up? mine was standard at 130 and is now fitted with a 155 , may even go to 160 yet if it doesnt cock it up...(I do have a gianelli pipe on though)