small 2 stroke engines

[cnelsonplumber]

I mixed up a new batch of fuel at 35:1 but the problem persists. Think I will follow your advice and have the carb off to check the gaskets either side.

 

[Merry]

I'd recommend checking the fuel and impulse hoses for cracks, especially if it's had stale fuel in it. I'm not familiar with the Mac 338 but if it's like most other chainsaws the impulse hose will be a bit of a bugger to check as it bridges the gap between the carburettor/tank housing and crankcase/cylinder and you'll struggle to see anything. You might have to remove it to inspect it properly which can be a bit awkward, but nowhere near as difficult as putting it back on afterwards. It's not unusual for the impulse hose to fail, (particularly if it's had old mix in it) due to the high vibration levels.

If the hoses are all intact then, it could be worth checking the carb for a blockage. If you remove to pump side cover (most likely held on by one screw in the centre) you can check the diaphragm which might need a clean but should be intact and the fuel strainer which is a fine metal gauze. Remove it carefully with something pointed and check it is clean - you should be able to see light through it if you hold it up.

Alternatively, if you've been using it with stale fuel for a while it's possible that the engine has started to seize. This is easy to check for - just whip the muffler off and have a gander down the exhaust port. If you can see vertical scoring down the piston you'd better sit down - it's probably bad news