[:@] I have a well broken -in OS .91 four stroke that became hard to start and when it did start it wouldn't accelerate without quitting. This happened suddenly to a normally great running engine. Any help would be appreciated. I am going to re-adjust the valves, check the fuel system in its entirety and I wish I knew the factory settings for the low-speed needle.That info would be helpful. Thanks

You might try a tank of fuel from another flier and try a new plug before doing all the extra work.

When you've got the rocker cover off, check that the valve springs are OK.

I replumbed the tank put in fuel from another can and reset the valves. The springs are OK