Chainsaw Repair

This is a 1991 model that has been sitting up for a while.  I put some fresh gas with staybil in it but did not remove the roughly one third of a tank of mix.  Might this be an ethanol issue?  Dump out all fuel and try again?  Thanks.

If it was running normally when put away then the most reasonable assumption would be something fuel-related issue. Another possibility is the fuel tubing could have deteriorated over time. When that happens, the tubing walls become soft and prone to partially collapsing. Is it possible to pull the carb apart? Good luck with all that, let us know if you make progress. 

It's not unusual for a saw to develop problems with the crankcase seals and exibit the same type symtoms  .

The seals do just fine until they run a short while then heat up because they've lost their resiliancy .After it sits a bit and cools some it will fire back up and run for a short period of time then once again die on the vine after a short .

Some can go for years and some cannot .

I suppose I've worked on ten series McCulloch more than any other combination of saws .In all that time until recently I had never seen a seal go bad .Then out of the blue two saw started leaking and ironically it was the very last year of production of the model 10-10 which looked for all intents as if were brand new .The other was a later model 700 .

Conversely I now own a Stihl 038 Mag that I nursed back to health so many times I've lost count .It  spent a hard life of 22 years in service for a tree service company .I know in a ten year period I changed those seals at least 3 or 4 times .In those years that saw never sat idle more than 3 months in a row and that was only when I was scrounging parts to repair it for the umteenth time .

Most recently it was a seal problem on a Stihl MS 200T which I submitted a thread about .It had  basically the symtoms you suggested  about the saw in question .It got progressively worse as time went on .I had blamed the carb but that little pot licker fooled me on that one .

Thanks for all the replys and sorry for taking so long to get back to my own post....  I'll try to dump and replace all the fuel.  To get to the fuel pick up do I have to open up the tank assembly?  The line that is easily accessable seems in good shape.  And not to be dim, but where is the tank vent?

I should also mention that a number of years back when I was using the saw more, it leaked after doing a good amount of cutting.  It may not have been pushed as hard since, but that problem has not happened again.  Heat/seal related?