Hi Grumpy, did check the chain brake just in case it wasnt coming off in the off position, all good. Runs perfectly without chain/bar on, will rev up instantly and idles no problems. Was having a look this morning and found the bar had a slight bend in it right were it bolts on, thought maybe its touching the clutch ( knew it wasnt, theres to much room) but straightened bar back out and decided to put it back together just to see what would happen. Kicked over straight away, let it run for a little bit, turned it off. Sat down at work bench and could hear a fiant noise coming from saw, listened hard and it sounded like air being sucked into fuel tank. Maybe it wasnt running for long not getting enough fuel due to vacum. Took it all apart thinking it might be the air nipple on fuel tank is blocked,wasnt, put it all back together, wouldnt start so i let it sit for awhile. Kicked over again first go, was running for about 1 minute done a wicked backfire and chewed flywheel key in half. Big lesson learnt, come and read what you suggest first. Will now go check what you suggest, basically chainsaw will run until it hits a certian tempreture then stop due to expansion which will cause loss of compression, yes??
