Farmall F-20, It lives!!

Hi everyone,

Some of you probably know that I have been working on a old F-20 that I got this past fall which had some spun rod bearings. I am glad to say that thanks to the help and advice from many of the members on here, this F-20 lives again!

After cleaning up the crank, finding a set of new bearings, and reassembling the engine, it pretty much started right up this past weekend! Just changed the oil today for the first time since doing the work and it didn't show any bad signs. Now it has some fresh 15w-40 in it and runs pretty good. The only downside is that after I changed the oil and brought it out today it decided to spring a rather large leak at the bottom of the radiator. Thankfully I have a spare which (I hope) is good and usable.

Attached is a picture and a link to a video of it I posted on Youtube.

The only questions I have are related to it running a little rough. Mainly the fact that when its idling it seems to run best in the "Start" or the middle position on the magneto. If I put the magneto in the "Run" position or all the way down, it seems to sputter a lot more. The only difference is when it is on the road in the road gear, if I throttle it up and switch the Magneto to the "Run" position it seems to throttle up much more and get a lot more power, but it does still sputter and backfire a little through the carburetor and sometimes seems to cut out a bit but other than that it runs like a champ. Not sure if this would be a carburetor problem or magneto problem since I didn't touch the mag and for the most part it runs great in the run position at higher speeds. Someone did mention that F-20s were known for idling rough but much better at higher speeds so not sure if thats it or it needs some tuning. If anyone can please advise that would be appreciated.

Also, I might as well ask while I'm posting about it, which jet is the idle and which is the main jet on this carb? One is right above the other and the top one is smaller than the bottom I think. Might try adjusting it once I know which jet is which.

Thanks and enjoy the video,

FarmallCT

Farmall F 20

Nice looking F20. Changing the spark advance between idle and full throttle is normal. A little more fuel might help but I bet just actually running the tractor will be the best thing for it. Are you going to paint the tractor or leave it its work clothes? Good luck, Mike

Tweaking the mixture might make it smoother, but with no muffler, the sound is going to be rough for one thing. Another idea is that when at low speeds, a retarded timing is going to be smoother than advanced. At higher speeds advanced timing will be smoother, and produce much more power. It is th reason centrifugal advance in distributors was easily accepted by farmers. You just need to do it manually. Jim

very cool!

That makes sense. I haven't ever really run these bigger F series before now so I wasn't too sure if it is okay to leave the mag in that position at idle and change it when at higher speeds and under a load. Thank you. If you know which jet is which on the carb that would be appreciated too so I can try and tweak that a little more. Thanks again.

~FarmallCT

Thanks! Ah okay, I haven't run these bigger F series much so I wasn't too sure if it was okay to run it in a position other than full run for longer periods of time such as letting it idle. You're right, I've been trying to run it and work it a little and the more the run it the better it seems to run. Once I figure out which jet is which I will probably mess with the fuel mixture and try adding a little more like you suggested.

As far as painting I am not sure yet. The tractor is in pretty solid condition and the rust isn't too bad so for now I think I will leave it in it's work clothes. I am thinking about painting it sometime in the future or if I have to take it apart again just doing it while its apart. I will admit, I do like the look of it as it is in it's work clothes and I am hoping to take it to a few fairs and shows as is before I eventually get to painting it.

Thanks again,

~FarmallCT

She would run better with a gas manifold on it.

A clear coat of semi-gloss acrylic would stop further loss of that fine original paint. It would look pretty much the same.
At Idle, one of the screws will do little or nothing. (probably the top screw) at work, the other screw will make a difference. Jim

You ask about the carb adjusting screws, the small one on top is the idle mix screw, the lower one is the main.

Before adjusting, make sure the air cleaner is clean (not just the oil cup, but the upper portion also). Be sure there are no vacuum leaks, the fuel is clean and good fuel supply to the carb.

To adjust the idle, get the engine up to operating temp, mag in retard position. Note the position of the screw slot, make small adjustments, remember which way you turned it so you can go back to where you started.

I believe on the Zeniths, turning the idle mix screw IN makes it richer, OUT makes it lean. So, back the screw slightly out until it runs worse, then back in to best idle, then about 1/8 turn more. Just play with it until it idles best, then slightly richer.

On the main adjustment, turning it IN leans the mix, OUT for richer. This is best set under load, which is near impossible to do. The next best is to set it by observing the throttle response.

With the engine running at full governed speed, mag advanced, manually pull the throttle linkage to idle. Release the link and the governor will full throttle back up to speed. While it is coming up to speed, listen to the engine, watch the exhaust. Again, note the position of the mixture screw. Turn it in 1/2 turn, try the throttle response. Keep turning in until the engine stumbles on acceleration. Then start backing the screw out, testing at each adjustment. When it is right, the engine will come up to speed without hesitation. A puff of black smoke is a good indication it is right.

Don't be afraid to play with the adjustments, each carb and engine is different, you will know when it's right. The carb needs to be in good working order to properly adjust. If it's flooding, or has clogged passages, or if the idle screw makes no difference, it will need to be repaired first. If this tractor ever gets worked, a plug check will tell if it's right. They should be clean, not black. If black, it's too rich. Any change to the exhaust will change he mixture. If you put the muffler on you'll need to readjust the main.