i am having a problem keeping my mgt .21 running properly.
it starts and idles fine and sometimes runs for several minutes without fault and then will just suddenly stop.it will always restart ok and will sometimes run on again for a while before stopping again whilst other times will just stall as soon as you try to pull away.there is no pattern to it but on average it is doing it about 7-8 times per tank.
i have both the lsn and hsn only a quarter of a turn in from stock and it is perfect when running,if only it would stay running.
the only thing that i have noticed when looking is the odd air bubble now and again in the fuel line.is this likely to be the cause or are there other things that i should be checking.the truck is almost new and has barely had any use but this is spoiling things as it is very annoying especially if it stops when it isnt near you.
please help

its not tuned properly.

get it warmed up, over 200 degrees:

HSN should be so it gets optimum performance at full speed but you still get smoke from the pipe. You shouldnt tune by temp but it is an indicator. Make a couple full speed passes and temp it. somewhere between 230 - 260 is good.

pinch the fuel line 1 inch from the carb. Should take 4-5 full seconds for it to die. If it takes longer, LSN is too lean, if it dies sooner its too rich.

If its not idled up high enough it wont stay running either. I always take the air filter off when I install/reinstall an engine just to be sure that the servos are set correctly that carb just opens all the way up at full throttle and that the idle isnt set so low that hitting the breaks will kill it. Generally, there should be about a 2mm gap in the slide opening in the carb. Check this with the engine off obviously and the servos turned off.

i really appreciate that advice thanks
i think that my hsn must be pretty close as at the stock setting it would splutter before changing into 2nd gear so i gradually leaned it off until it ran cleanly,which ended up being a half turn in from stock.
as for the lsn i had heard of pinching the fuel line and counting how long it takes to die but wasnt sure of how from from the carb to pinch it so that has answered that one
cant do the temp reading as a thermometer is the only thing that i need to get now and that will have to wait as i am skint after just forking out on a receiver battery hump and a fail safe
many thanks.
jas.

ok just did the pinch test,first run was about 6 secs so i opened the lsn up by about 1/8 of a turn and the second run was spot on 5 secs.did another couple of runs to be sure and again spot on 5 secs so hopefully all will now be ok
speaking to my local hobby shop owner earlier and he said that i may have a few problems in the beginning as the thunder tiger .21 engine that my mgt is fitted with takes a good gallon of fuel before it is run in properly and mine has done nowhere near this amount yet.does this sound like good info or not.