Yeah, I suspected the gas too. I also read in the user manual that Stihl recommends high octane gas for those big saws. Trouble is, where I am you can't get high octane gas. The manual also recommended running the engine dry if you were going to leave it sit for 3 months or longer. Trouble is, if you can't get the @#!%! started, how to run it dry?Hey, Gary!
The biggest problem for any 2-stroke is old fuel. Not that which you mix fresh, but that which remains in the carburettor after running. If it sits for a month or longer, you can be sure that the volatile part (the fuel itself) has evaporated, which leaves only the thicker 2-stroke oil behind. This residue becomes sticky and gums up the insides of your carb.
As a rule, each time I put my saws away for longer than 2 weeks, I will religiously empty the tanks and then run the saws dry. When they stop, I choke them and run them again. Sometimes I can get them to start 3 or 4 times "after" empty. (It is this residual fuel which is normally left behind in the carb).
You mentioned that once they are running they are fine. This is consistent with "gummed up" carburettors, which, when warm, allow the gummy goo to be dissolved and flushed out.
Maybe you could try this method too?
Hope this helps!
Mike
P.S. Stihl recommends not using any fuel older than 6 weeks from the date of mixing. No part of the fuel may be older than 6 weeks, since the lubricating properties are severely reduced.
I bought two drums of gas that came right from the refinery and got them up to my village. Then I mixed the with Stabil to stabilize the gas. I also have a product called Octane Booster, but I've been advised by someone here not to use that on 2 stroke chain saws. I also got me some metal "Gerry" cans to keep gas that I've mixed, you know, the ones that are illegal in California for gas. With those cans you can't even smell any gas scent which means it will keep the gas longer. But these plastic "approved" cans nowdays are a bad joke.
What's troubling is that I have a Stihl MS 651, and it never gives me any problems. I also used to run two Stihl 090s for years sawing lumber and felling and never had any issue starting them either. Never. But these new saws are a different beast.
I downloaded a service video from Walbro's website on servicing their carburetors. I'm also stocking up on parts and new carburetors in case I have to go to that extreme. If I can just get these saws running, with all the advice here, I should be able to keep them running, Lord willing.
Thanks for your advice Mike. If I can get them started, I will surely run them dry before sitting them down for any length of time. Just as soon as I finish any sawing job and going to something else.