Missing F-20 - - Wednesday update

1) Can someone check their valve timing? Per the book, #1 cylinder should close its exhaust valve slightly before TDC, and open the intake valve just past TDC. Though this seems right, my tractor's valve cycles were running about 10 degrees late in the cycle. I adjusted the timing gears 3 teeth to get the cycle back to where the book said they should be.

2) Has anyone ever tested the vacuum on their intake manifold? I ended up drilling and tapping a hole (1/8" NPT) on the forward horizontal leg of the intake manifold and installing a vacuum gauge. Am only pulling 10-12" vacuum at no load speed. Seems low. Can you check yours?

3) During examination of the carburator innards, the die cast venturi has a couple flats cast into it on the outer flanges. It appears one is supposed to lock into a tab protruding from the main jet. Is it critical that this tab locate with the flats in the venturi, or anything else?

4) Some of you guys indicate frequently missing as "the nature of the beast" for F-20s when the spark is advanced and under no load. Are there some of you F-20 owners that have tractors that purr under any condition?

5) Last thing - - My tractor has an older aftermarket gasoline-only manifold with the letters HF122-L cast into it. Others of you have this manifold? Those of you with it, do your engines run smooth or miss when the spark is advanced under no load conditions?

Thanx all. Will keep you posted with my findings.

Pete

I've never disected a tractor magneto, but i've worked on a few hit and miss engines and I have rebuilt distributors. My question is this: Doesn't the F-20 and the other F-series tractors need the "spark advance/retard" lever in order to adjust the timing for various RPM's? Again, i'm not sure if the mag is internally advanced, but i've seen a whole bunch of F-series tractors that were missing the spark advance lever.

Theoretically, you could have the mag set perfectly but it would be timed for a set RPM and therefore would run best at that specific RPM and progressively worse the further you went away from it.

Could it be that your mag is properly set but for a full load RPM and the lack of spark advance is making it run too advanced for the low speeds? I kid you not, this answer came to me in a dream last night and I had to share it. Just my thoughts on a possible fix.

Jeb

JG