2010 - Volume #34, Issue #4, Page #35
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Farmall Cub Runs Great On Chainsaw Carburetor
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"As far as I know I've got the first Farmall Cub in the world with a chainsaw carburetor," says Peyton. "I came up with the idea because the carburetors on Cub tractors are famous for being unreliable, leaking fuel, and starting hard. I had to rebuild the carburetor on my Cub 3 times over a 2-year period but it still didn't run well," says Peyton, of Huntsville, Mo. "I know people who have junked their Farmalls because they couldn't make the carburetor work and couldn't find a good replacement.
"I priced a newer replacement carburetor, but the $249 price tag encouraged me to seek alternatives. I'm a retired engineer and mechanic and have a lathe and a Bridgeport vertical milling machine, so I figured I could come up with something better. I decided to use a chainsaw carburetor because it develops a lot of power for a small engine, and because it's designed in such a way that it can operate in any position. The Stihl carburetor's bore is larger than the Cub's, so I knew it would have adequate airflow."
Peyton says his homemade carburetor has worked even better than he hoped. "The tractor now starts instantly, is more reliable, has more power, and doesn't leak fuel. Also, it's more fuel efficient because the Stihl carburetor does a better job of atomizing gas."
The tractor's original air filter was under the hood and the air intake above the hood. They were no longer needed so Peyton removed both of them. The chainsaw carburetor originally was equipped with a built-in fuel pump connected to a small fuel line, with fuel pumped by pulses in pressure from the chainsaw's crankcase. But on the tractor, the carburetor had to work with a gravity flow system, which required modifications. "The fuel pump side of the carburetor had to be altered, sealed and tapped so I could run a standard 1/4-in. fuel line and fuel filter to the tractor's gas tank," says Peyton.
He machined a new governor linkage bellcrank and pivot, as well as an adaptor plate and air filter mounting plate, which were machined from aluminum bar stock. The carburetor's adjustment screws were shortened and re-slotted to allow for the bellcrank and governor link. Linkage from the bellcrank to the carburetor was fabricated, and the governor linkage was modified where it screws onto the carburetor.
"I wanted to use a modern paper filter and found one that was designed for a Tecumseh engine. But in order to make room for the air filter I had to shorten the tractor's oil filter tube," says Peyton. "I also had to discard the tractor's large, breather-type oil filler cap. I fabricated an O-ring sealed oil filler plug with a folding handle and a dipstick that threads into the center of the plug."
The tractor didn't have a "breather" cap on the oil pan, so Peyton fabricated a positive crankcase type of vent system. A rubber hose allows blowby from the engine crankcase to vent into the carburetor's intake airstream.
"I paid $2.49 for the fuel filter and $4 for the air filter. I also bought 2 clips to secure the governor linkage to the carburetor, 2 long screws to mount the carburetor, and 2 brass fittings that are part of the positive crankcase vent system. I got the carburetor free from a man who used to own a chainsaw dealership. I already had the fuel line. My total out-of-pocket cost was only about $11.
"The Cub's original carburetor wasn't adjustable, but the Stihl carburetor has 3 screw-type adjustments, one for high speed, one for low speed, and one for idle speed. I use the tractor to plant and cultivate a 1/2-acre garden where I raise watermelons, potatoes, sweet corn and beans. The beauty of the Cub is that the planter and cultivator mount between the tractor's front and rear wheels so the driver has a good view of everything."
Contact: FARM SHOW Followup, Paul Peyton, 4373 Hwy. D, Huntsville, Mo. 65259 (ph 660 998-4204; peyton.paul@gmail.com).
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