SawTroll
Information Collector
To OP,
pull the muffler and look at the piston through the exhaust port. if the piston looks like below pic it's lean seized.
If piston doesn't look like above you'll have more poking around to do. 90% of these saws torch themselves on a lean condition. You don't need a bigger venturi carb so don't let Troll scare you off the saw. They just need carb adjusted properly to get more fuel through to help keep the saw cool. Most good Dolmar shops (like Ford150) know to make this adjustment right out of the box. Some don't and you end up with a torched saw. I know tree services running 5100/5105's with richened up carb settings for several years and they beat the snot out of their saws.
Pull the muffler off... it will take you 5mins to check for lean seize. If you look good there come back and will work you forward from there.
You are right that sub-standard dealers was a large factor in the unusually high failure rate of those saws (5100S and early 5105) - they should have corrected the lean factory setting of the carb when selling the saws, but way to often failed to do so.
The reason for the lean factory settings was that the saws were borderline vs. EPA regulations, so they had to be set that way to be allowed in the US.
I wouldn't be afraid to rebuild my 5100S if needed, you just have to keep a close eye on the carb setting - and avoid prolonged cutting in hot weather.
A larger carb or not is a moot point to most users, even though it might be a good idea with ported saws.
