MAC 120 Chainsaw won't idle


Old 05-22-07, 05:26 PM
Thread Starter
Join Date: May 2007
Posts: 1
MAC 120 Chainsaw won't idle

I have an old mcculloch MAC 120 chainsaw that I'm trying to start (without the bar or chain attached.) It has been sitting for over a year, properly stored. I have cleaned the carburetor fairly fully taking it mostly apart and getting spray carb cleaner on everything I could spray it on.

The chainsaw will start if primed in the choke hole with a little gasoline and will then run as long as the rpm's stay up fairly high. As the rpm's fall down, the engine seems to just stop firing as opposed to slowly puttering out.

My two guesses are that the fuel filter is too clogged. Some gas is obviously making it through as the engine will run as long as the throttle is fairly open and the rpms are up. I'm not very sure how to gauge how clogged the filter is, gas will get through the filter due to gravity, but not much more than a quick drip.

The second guess is that my carburetor is goofed up somewhere, either in the diaphram or some other place, maybe the low speed adjustment screw. I have tried playing with the screw from stand adjustments to just about anything i can think of with no avail.

Any suggestions would be appreciated.

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Old 05-23-07, 02:22 AM
puey61's Avatar
Join Date: Apr 2004
Location: Upstate New York
Posts: 3,224
It sure seems to be a fuel starvation issue related to the carburetor and you'd then want to soak and recondition the carb with a rebuild kit. Since McCulloch parts are near impossible to obtain but, since, the carburetor is aftermarket and likely either a Walbro or Zama, you can find a local repair shop that has such parts and take the carb, in hand, and purchase the manufacturers rebuild kit for your carb.
Old 01-26-11, 01:21 PM
Join Date: Jan 2011
Location: italy
Posts: 1
Mac 120 carburetor rebuild

I too have a Mac 120 & am in need of a carburetor rebuild.
Is there any way to tell which make/model I have - short of dismantling it?
(e.g.: based on the serial #?)
I live in Italy & the local shop has already told me it's impossible (and that I should throw it away!)
Thanks in advance, Wm./

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