Good Info/History! I feel we are still missing something, BUT WHAT?

1. When it starts from a prime does it run with good power, then as out of fuel vs compression or spark (slow vs instant)?
2. Have you checked your fuel X age/trash/moisture/Stuff and lines/filter X restrictions at connection/compressions/bends?
3. While in the carb, did you check the Carb's H&L Adjs X clear and small screen X restrictions (w/compressed air or carb cleaner?
4. Your info sounds like restriction or contamination due to it being sudden vs a bearing IMO (Opinions?)
5. Do you use stabilizer in your fuel or a dose of carb cleaner on a schedule?
6. Last, should have been first, what were the over-all conditions from extended sitting (tank/carb/lines)?

Good Fire/Fuel/Compression are the basics to running. Good Luck! loger

The problem with diaphrams? It's really hard to tell if they are any good unless you see hole in them. So of use can guest by looking at them and again it just guest? The diaphram is the fuel pump. Gives the initial squirt of fuel for the saw to rev. and unseats the needle against the seat for fuel flow in conjunction with the vacuum of the pistion going up and down pulls fuel up to and through the carb.

Other problem You said you cleaned the carb. But didn't eleborate on how and what you did. Under the diaphrams there are welch plugs this provided a path to clean the three main jets. IF the saw will idle and won't rev up sometimes the mid and full throttle main jet has become blocked with something dirt, gum,or whatever. Most of use don't miss with the welch plugs due to special tool for installation being it's just hammer seal conformed to the opening in the housing.

Mostly likely the main jet is clogged. you can try to spray can carb. cleaner in ALL the little holes when you have the carb. apart, but that don't garrantee it will clean the main jets passages. Again assume you have checked the filter in tank all fuel line aren't cracked and you have got all the air out of the fuel system?

Replacing the small int carb screen was a challenge but learn to leave them in the many piece kits as the welch plugs. I tried to pay to have one replaced and the Shop said they are too simple to install with the correct punch or pencil�s eraser. I d/n find that to be true but with a punch I finally installed it close enough (the old one cleaned). Seeing that the mechanics under the screen was clean was my objective.

The opposite from another mechanic was, "you do not replace it". This is when you have to be the Judge from your experiences. Which leads me to cleaning vs removing/replacing. It looks simple but I c/n find the touch. loger

PS. A very good displays at the address below will show the welch plugs and screens. Plus, this info address installing the welch but not the screen.

http://www.aerocorsair.com/id27.htm