problem with M3414 chainsaw

Gidday,

Got problem with a M3414 chain saw.

It runs for about 3 to 4 minutes then cuts out and will restart after a minute or so.

I put a spark tester on it and watched it run, there was no problem with the spark and it was still throwing sparks as it died.

Tried changing plugs, no difference

Fresh fuel no difference .

Pressure test crankcase all fine, vacuum tested same, again fine.

Pulled the carb off & it pressure tested OK.



Now here is the interesting bit, the fuel supply line squirted fuel every where when I took it off as if the fuel tank was pressurising and forcing the fuel out.

So I tried it again and same thing, the tank seems to be presureizing.

Even just pumping the remote primer for long enough pressurizes the tank



Now I know very little about specific chainsaws and even less about this model.



So does the fuel cap on this model have a two way vent ? an one way vent or no vent ?

Any one have tis happen to them ?

Any ideas ? I am totally stumped on this one.

I even put a pair of kits through the carb ( cheap Chineese Walbro/ Zama hybrid ).