Farmall F-12 Fuel Issues

Hello All,

I have a '36 Farmall F-12 that I rebuilt a few years back and I am constantly struggling with fuel issues. The tractor will start pretty easy but when running, sounds like it misses a cylinder every 2 or 3 revolutions. The exhaust is usially putting out a dark colored mist and after running for a while, the vent port in the exhaust manifold will start dripping black fluid that gets all over the left side of the engine. I have also notices that when running, it seems to be excessively louder than other F-12's in the area. It almost sounds like the engine is under a light load when at idle (which leads me to think it is a timing issue).

The tractor had sat for about 60 years before I got ahold of it. I had the magneto rebuilt, along with all new cap, rotor, wires, plugs. Rebuilt the original carb, correct valve lash, new piston rings. I even bought a new carb to put on thinking maybe the original was the issue, but so far, no luck. I have tried messing with the fuel mix screw, but that seems to do nothing. I have not touched the timing at all because it starts fairly easily.

Does anyone have any knowledge with these to know where I should start looking or continue looking?

Thank you all,

Dalton

If tractor is equiped with the F-4
mag, I presume you know about the
spark advance adjustment? The smaller
lower cap on mag that goes over the
points. Off to the side of that cap,
it has a whole for a lever (lever
might be long since gone). That cap
essential adjusts the timing a few
degrees. All the way up, it grounds
the spark to kill the tractor.
Operator was suppose to adjust the
advance along with throttle RPMs. The
more throttle, the more on the advance
adjustment. If equiped with an F-4
mag, your not by chance running the
tractor all the time with the
mentioned cap just down a tad from
being in the kill setting, are you???
This would actually retard the spark
and give it more of a bark in the
exhaust if ran that way. More so as
the throttle is opened up. People
usually (especially if lever is
disconnected and gone) just run all
the time with spark all the way
advanced (cap adjusted all the way
down). If you know all about this, and
that's not your problem, maybe mag is
perhaps a tad bit out of time with the
engine creating the extra bark.
Either way, it has nothing to do with
your fuel problems on the other side.
Can't explain the messy leakage. Maybe
try to clean it all up, and trace the
leakage back to its source. Find the
problem that way. I actually don't
have an F-12, but rather the bigger F-
20 (same mag, different fuel system).
Always heard tell of the 12's having a
fuel pump, and the pumps are
cantankerous and problematic.

Thank you for the info. This tractor does have the F4 mag and all original levers. I didn't know that the spark advance lever was to be adjusted along with the throttle. The only way I learned how to run this tractor was through the owner's manual, (which I may be misinterpreting) so I advance the lever just a little above 'kill' in order to start, then go to full advance at all times when the tractor is running. I do notice that when running at idle, the tractor runs quietest at full throttle advance, then gets louder as the spark is retarded.

So my next question is: At what spark advance position should the tractor idle smooth? Since the lever only travels from about 10:00 to 2:00 position, should I get a good idle around 11 or 12:00? maybe i'm missing your point completely?

Back to the fuel side, there is a fuel pump which pushes fuel up to where the hood meets the fuel tank. There is a 'T' in the line there, one side runs back into the tank as an overflow for the pump, the other side connects to a gravity-feed line for the carb. I took that T out and made sure there were no blockages, so far everything is clean.

The vast majority of the black fuel/oil is coming out of the exhaust manifold. There is a little open port at the bottom of the manifold that points toward the governor and throttle lever area. This is the area that gets coated with most of the black goo.

Normally my O-12 is run at full advance. The wee hole in the bottom of the exhaust manifold is a drain to let any water etc. that comes down the exhaust pipe to drain away and not go into the cylinders. I have never had any mess come from that hole. The T allows most of the fuel pumped through the fuel pump to go back to the tank, there is about a 1/2 inch head on the line to the carburetor. The kerosene F-12 tractors had a special header tank which fed the excess fuel back to the input line to the pump to prevent mixing of the kerosene and the starting gasoline. The O-12, W-12 kerosene tractors had a starting tank in the hood which avoided the fuel mixing problems and the later F-14 kerosene tractors also had the starting tank shifted from its earlier position in the back of the main fuel tank to a small tank in the hood.

Basically the total time of the spark
to when the explosion actually
happens, remains the same length of
time no matter what RPM you are at.
But changing RPMs (engine speed),
changes the exact point of when the
explosion happens. The spark advance
makes up for this slight difference.
That way the explosion don't happen
when piston is here at one RPM, and
there at a different RPM. Faster
engine speed would move the piston a
little further ahead at time of
explosion, if spark was fixed with no
advance. Make sense?
That said, if timing is set right, the
advance actually can be retarded
further than need be at idle. Some
where around half on the advance at
idle would be about right. They left
some wiggle room between there and the
kill setting. Engine can run just off
the kill setting, but at that point,
it's just a tad retarded for idle.
Since this is all just mannuely done
by operator, there really is no
perfect way of doing it. But
understanding the concept of it, gives
the operator a better idea of what
thier doing.
I'm afraid my advice for you is
somewhat limited to the mag side.
Meaning, I'm not familiar enough with
a 12 fuel system to tell you what your
problem is on the fuel side.
Only responded because I'm familiar
with the F-4 mag. It was used on
numerous models.

I thought that's what you were getting at for the spark advance. I may need to dig the tractor out and play with the timing a little then. I have it set to where the engine idles at full spark advance. To set timing, I was under the impression that unbolting the impulse coupling shaft, and moving to the next closest holes that line up with each other? In this case, I would want to advance the spark correct, since i will be retarding the spark by idling at around 12:00 position? Would it be possible that the mess is coming from unburned fuel spitting out the exhaust when the engine is above idle and running a retarded spark?

I figured the hole in the manifold was to let out any unwanted fluids (rain) etc. I haven't been too far into the head of the tractor, but could it be possible that there is some oil blowing through the valves? I know I still have the original felt in the valvetrain to retain oil, is it likely that the oil is running down the valve stems when the tractor is off or running?

I have a 14, and once its running, I leave the advance alone, idle or not. Theres a procedure to set the coupling, but I dont
recall exactly what it is. If its starting fine, leave it alone.

Thank, John. I was just wondering if I should advance the spark a touch just to knock down some of the exhaust sound. Guy down the road is running 2 F-12s, one with a muffler, and one not. Both of them make mine sound like a Harley. The exhaust seems to have more of a CRACK to it than a normal putting sound.

I wouldnt touch the timing. You run the risk of it not being retarded enough to prevent possible kick back. When I first got my 14,
I set the advance to around half way, 2nd pull of the crank sent me to the ER with a broken wrist.

(quoted from post at 13:34:58 02/17/22) I wouldnt touch the timing. You run the risk of it not being retarded enough to prevent possible kick back. When I first got my 14,
I set the advance to around half way, 2nd pull of the crank sent me to the ER with a broken wrist.

Click to expand...

agree, and only want to change the timing if I'm convinced that I truly have it wrong. I had a similar situation right after I rebuilt the tractor. I had the timing way too advanced... I was taught to always start the tractor on the upswing and never wrap your thumb around the crank.. When I went to start it for the first time it kicked back and the crank hit the top of my left hand on the follow through. It was sore for about 2 weeks after that... So to your point, I really don't want to touch it unless that is a possible cause to my issue.

If you got hurt from a kick back, I'm guessing you were likely hand cranking it in an unsafe manner.
You shouldn't crank in a downward motion. Only upwards. Thats the reasoning for being able to engage the hand crank at half hitches. So, there for you should never hand crank in a continuous circular effort either. Cartoon characters do it that way in the cartoons. That way was wrong, and intended to be funny in the cartoons, but in modern day, the joke seems to go over people's head, because they don't know anything about it, and do as they see in the cartoons. Thumb should be on same side of crank handle as your fingers, and pulled upward with only that one hand. And you should also pretend there is a glass wall in between you and the crank. The only part of you that should go through the imaginary glass wall, is the one hand and arm you are cranking with.
I had to learn some of this the hard way. I got my arms twisted up in a crank one time so bad, it twisted me right off my feet. That's the day I learned about the, not using two hands part.

Actaully, I was doing it correctly. There were several factors in play though. First was lack of experience with the F-14. Npot having my Dad around when I got it back, long story, to know where to set things, and the few people here back then who had the right knowledge to assist me, had me setting the advance just off full advance, instead of OFF. The ujoint was completely shot but it worked so spinnig wasnt going to be an option, but I did have to kinda go longer into the swing/pull than I do now after repairs, and generally not knowing the tractors personality like I do now. Its been a couple of years now since Ive had the stremgth in my hands to hold the crank tight, and it has ran for that long, but I finally got it to where it would start of the 3rd or 4th pull after sitting for months.

Good deal. I think everybody needs that first time kick back just to understand the power of a kick back and more importantly how to protect themselves after that. Unfortunate for you, that you got hurt.
I have an H with a distributor that I hand crank all the time (starter push button don't work, and replacements are JUNK). A kick back is always a possibility hand cranking that. Have had numerous kick backs on that. So, I guess I'm trained on hand cranking the right way. LOL.
Hand cranked my F-20 one time when it was really cold, just to see if it would fire over. Set advance where I normally do. Pulled crank twice with carb on full choke. Released choke, gave crank another pull. It kicked so hard, it ended up kicking the hand crank out of my hand, spun around one revolution and thats when the crank left it shaft, and flew over and hit the H in the hood, bounced off that and hit me in the leg. That was a big eye opener, to not be in the way of a kick back. And also, not to set the spark advance where I usually did.

Dalton, listen up, I many of these tractor been there done that. Had a friend could not get his F-12 to run or start easy
most time we pull started it. Slobber out exhaust and wep hole as you say. After changing the mag the carb, we found that he had a internal
crack in the manifold when running it would push fuel out exhaust and smoke black, no adjusting the carb would help.
After trouble shooting about a year we put on a new manifold and it runs great and start easy. I hope this will save you from all the trouble
we had. Never had a tractor beat me up so bad could not figure it out to a long time as we were not at it steady. oldiron29

Hi Oldiron29,

It's funny that you should mention the manifold being a possible cause to the issue. I had eventually thought the same thing because the original manifold had some hairline cracks around the pipe mount and severe rust where the intake/exhaust portions bolt together. Sometime around getting a new carb, I did also get a new manifold and gaskets to put on. Like you guys, i figured the problem would disappear with a new carb/manifold setup, but no luck. She still slobbers and sends black mist all over the left side of the engine. Seems like the most comes out of the weep hole in the manifold, and the rest around the pipe mount. I'm trying to get some pictures uploaded of the issue.







This post was edited by 14reamdalton on 02/18/2022 at 03:32 pm.

My f=12 (1937) had raw gas leak. Cost a pretty to have it restored. Welding shop had the pros who could weld bevel gears on a Timex watch. That
manifold wasn't like yours & I think it had (distilate) stamped on it.

Led

My M sits outside and rain will sometimes get down into the manifold. When I start it black liquid blows around until it gets dried out. Any chance you have a head gasket leak?

Dalton, I see you have new manifold. you say you installed new rings? original sleeves and pistons? If it has not been run much could it be
you rings are not seated yet? getting some oil by pass? or are you sure its fuel leaking?

Other thoughts, Have had some guys tell me they had over fueling problems. The fuel pump will pump more fuel than the carb can use.
There is a tee fitting at top of gas tank, the tee should allow excess fuel that the carb will not take back into fuel tank.
You must make sure tee is open and flowing not blocked. have heard some guys drill them out so opening is a little bigger, may not clog that way. Also carb float could be adjusted so bowl level is lower, this may help over fueling problem.
Main fuel screw should be screwed in seated and backed out 2 turns. Air screw should be out about 1-1/4 turns, than adjust for smooth idle
when warmed up.

You might want to take care of your rain water issue. It don't take much to get into a cylinder and freeze up the engine.
My M had a loose kind of iffy rain cap on the muffler. Kind of blowed around and didn't always cover the entire exhaust hole when down. It sat for a long spell, and froze the engine. Luckily I caught it before it froze up the engine very bad.

I did put new rings in a coupe years ago, but I don't run the tractor much at all. It's more of a show piece/family history for me, and (being on steel wheels) is kinda cumbersome and damaging to anything it touches. I replaced the rings around 2017 I believe, but the tractor only gets an absolute maximum of about 5 hours run time each year. I run it only in the summer when everything is hot and dry and it can't carve up the yard. So I suppose maybe the rings aren't seated right or could very well be a head gasket. it's hard to tell whether the substance is oil or fuel, though as you can see from the pictures it fades to a grayish black as it "dries". Normally, as is runs, the fluid is jet black and oily to the touch. This kinda steers me away from it possibly being water. I have dealt with my H sitting out in the rain and blowing black mist everywhere when I start it, and this is not the same substance. I have checked the fuel T at the tank and all seems clear. There is still some junk that breaks loose in the tank from time to time, but I have 2 sediment bowls with screens that should catch the majority of the big stuff.

I am going to try re-setting everything on the carb and see where that gets me. maybe just running way too rich? There is also a spark miss about every 3 rpm at idle speeds, could that be bottling up unburned fuel and kicking it out the exhaust causing the issue?

Dalton, Just a question what did you torque the Head to? I use spec. for farmall ABC 113ci should be 75-80 ft.
If you think it could be water retorque the head and adjust the valves again, no cost involved.
Hope if you go through some things you may find your problem.