The cylinder on the mower is reminscent of the drone engine or the engines McCulloch was building for Reed Prentice before they went into chainsaws on their own.
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Dave86 - if you happen upon a stash of carburetors for the BP-1 saws I am in need of three.
I spent most of the day yesterday trying various things on these two, one is my runner from years ago and the other was put together from a large parts lot I picked up a few years ago. Both saws will run with the one good carburetor that I have, the other carburetor will seem to work for a while then the saw floods out. Either the material they used for the carburetors was low quality, or the carburetors that I have were stored in less than ideal conditions as they all seem to leak along the seams even with new gaskets and diaphragms. I can live with a little bit of seepage but fuel running out does not work.
At one point I even tried to use the carburetor from a 170 welder which looks the same externally, but when I tried to swap the throttle shafts (the arrangement on the welder is different than the saw) I discovered the welder carburtor has a much larger throttle bore.
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One reliable runner, one almost runner, and one really bad carburetor.
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I found it interesting that on several of the McCulloch/MAC carburetors (flat back and the BP-1) they opted for a fine screen rather than a more conventional high speed check valve. I know for some of the flat back models McCulloch offered a coversion kit to add a check ball in place of a sintered metal screen.
Mark
Brian Genrich sent me some additional gasket/diaphragm sets after the first round of testing. The updated parts worked much better, we were even able to get the second saw running and cutting today. It still has some issues as the primer is quite sticky, and it will tend to flood out if it sets and idles for too long, or comes down too quickly after a hard run. None the less, I now have two runners and pretty happy about it.
Mark