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mCculloch FR2.0


LawnSite Member
I inherited a Mac chainsaw. FR2.0 - it runs, wide open. If you let off the gas at all it dies. I took the carb out of it, didn't find any major debris or anything questionable. I put it all back together brought the H and L needles about 4 turns out. I got it goin and adjusted the high till it sounded like it was doin okay. The low needle wont change the saws performance, even with it closed all the way up.

What do you guys think? Weak pump/diaphram?

Fuel filter is new - plug is good.

Thanks in advance.



LawnSite Member
los angeles
Did you ever get that chain saw working? I have one and the little rubber bulb you press to prime it has torn away. How do I get another, or fix this?

Not very good with tiny gasoline engines.


LawnSite Senior Member
west Texas

About the bulb?

Below is a copy of a post a few days ago.


I have had problems with the "so called" primer bulb on echos and other small 2 cycle engines.

The bulb does not prime the carb, it just loads it with fuel if it is empty. To do this, it has 2 rubber valves (duckbill valves). With age they quit working.

I remove the bulb, cut a piece of plastic (freezer bag), place between the bulb and carburetor housing, then put the bulb (and metal plate) on.

This disables the primer(actually purge pump) and you will have to depend on the choke to start (cold start only) just like it was in 1990 and before.

The duckbill valves allow air to enter the carb irratically (when bad).