Yes, full warm up

personally i would bother adding a 2nd washer..persistent blowing of plugs can be many things,you really need to look at the plug element after its blown and tell us what shape the plug element is in..

is it all distorted,is it still shiny and new looking or gray coloured and dull.

Yes, as above

have a look..see if this helps

http://www.rccar.fiberworld.nl/images/glowplug.jpg

carnt see it being fuel, as you have 2 engines doing the same at 4 mins there is only one thing in common, at 4 min your fuel must be at one level in the tank, si id say tank/fuel line problem, if you stop and refuel at 3 mins what happens?
what temp is the engine running at at 3&1/2 mins?

Good thinking Mark, not tried re-fuelling at 3 mins but will try it.

It is difficult to say what temp its running at when it cuts, ordinarily it runs at about 105C, thats after staring it in the pits, keeping it running, and then doing about a minute and half of installation laps. But by the time we have recovered the car from the track its well below that, depending on whereabouts on the track it cuts.

Gonna replace the fuel tube, however when looking through it appears there are different bores, so what size tube should I use?

Anybody

any should be fine..i tend to use a big bore on the fuel line and a thicker walled pipe on the exhaust pressure line,just get some thats a good fit on the carb and tank nipples.

It varies quite a bit though, from 2.1mm to 3mm. Is it different for say a .12 engines as it is for a .21 engine. I dont want to starve it of fuel, but again I dont want to flood it.

the stuff i have on is just under 3mm,dont have my sizing pins to hand but a 2.9mm drill shank just fits in nicely and just flexes the sidewall.

Cheers Dave

you may find your nipple holes (ooo eck) are smaller than the pipe bore any way

you never told me it was a rossi engine you were having problems with!!! try another carb sounds silly but a few people have found the carb to be dodgy forget about your old GO engine i tried to make it run at Notts and got Pi55ed off with it

Anyways you have GRP Power now!!!!!