[Farmall] Bad K-5

[Robert L. Holtzer]

Nice info, Karl.

Bob Holtzer

At 09:09 AM 6/9/2005 -0700, you wrote:
>Some of you will remember the fun I had a year or so ago when I took my 
>'31 T-20 crawler to the Tulare, CA antique tractor show.  Basically I 
>never got more than ten feet from the trailer, despite many hours of 
>trying.  Water in the gas and a major flooding problem kept the engine 
>from running properly.
>
>Now that I have successfully rebuilt the Zenith K-5 carb on my F-20, I 
>decided to re-visit the carb on the T-20.
>
>When I rebuilt the carburetor about five years ago, I failed to completely 
>disassemble it.  I couldn't figure out how to pull the cast zinc venturi 
>out of the cast iron carb body, and I didn't pull the throttle shaft 
>because it is secured with tapered pins through collars.
>
>The venturi was easy this time.  I sprayed penetrating oil around it and 
>pushed it out using the hydraulic press and a rounded brass rod.  The 
>penetrating oil had wetted nearly the whole interface of the venturi in a 
>minute or two; I don't think it took more than 50 pounds of force to push 
>out the casting.
>
>The throttle shaft took longer, but drilling out the tapered pins went 
>very well using my mill.
>
>As expected, the economizer valve port was completely plugged with rust. 
>Worked away at it for fifteen or twenty minutes before I got the port 
>opened up.  All by itself, that undoubtedly made the engine run rich 
>throughout its midrange.
>
>As I was cleaning up the bore in the main carb body where the venturi had 
>been, I spotted some pits.  Closer exam revealed that they were probably a 
>combination of casting porosity and rust pits.  And when I squirted carb 
>cleaner into the pits, it ran out the fuel intake port of the carburetor.
>
>So what I had was a passage that bypassed the needle and seat entirely, 
>and let raw fuel drain into the passages surrounding the venturi, some of 
>which dump right into the airstream.  I was puzzled before by the very 
>high leakage rate I had observed.  I couldn't understand how most of the 
>one gallon starting tank managed to run through the carburetor and down 
>into the air inlet pipe in about fifteen minutes.  There's no way that the 
>fuel should have gone past the (brand new) float bowl needle and seat that 
>quickly.
>
>I dabbed some epoxy on the 'pits' and sanded it flush after it cured. 
>Hopefully this weekend I'll get a chance to finish rebuilding the carb and 
>try out the T-20.  Somehow, I think it'll run a LOT better.
>
>I've pulled the throttle shaft on four K-5's now.  Every one of them had a 
>plugged economizer valve port.  I'm convinced that is is pretty much a 
>universal problem.  And now I know that you MUST remove the venturi and 
>check out the main carb body behind it.
>
>-karl
>
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