Farmall F12 Black smoke and engine quits

Rob_D514

New User
Hello guys,

As a Belgian IH collector I'm new here, so first of all: hello everyone!

I immediately have a question for you guys: I rebuilt the engine from my Farmall F12. I also rebuilt the fuel pump and the carburetor. Now, the engine starts really
easily, after one push of the crank. The problem however: the engine doesn' run smoothly and after 10 seconds or so, it starts to blow black smoke. Eventually, after
some more black smoke, the engine dies and gas appears at the bottom of the carb (where it is screwed onto the manifold).

So, it seems that the carb is flooding/giving too much gas. Where do you guys think the problem is situated? What should I do first?

Thanks a lot for your consideration!
Regards,
Rob
 
Rob,

The first thing I can think of is take your carb apart and check your float. Feel it to see if it feels heavy at all. I know I rebuild the carburator on mine and had a similar problem, Eventually when I had the carburetor apart to make sure everything was clean and set properly, I realized that the float felt unusually heavy and it was filled with gas.
Another possible problem could be the drain for the fuel line is clogged. Not sure the proper name for it but it screws into the front top of the fuel tank and has a small drain so when the fuel pump is pushing more gas than the engine needs, it drains the extra fuel back into the tank. If it is clogged, then all the fuel the pump is pushing will be forced through the carb under pressure, and it is enough to force the float down so it continuously flows in.

I would start with checking both of these an seeing if that helps any.

~FarmallCT
 
Rob,Could be your float has a hole in it or your needle jet is not seating.Also sometimes your fuel pump is pushing to much gas,ive shimmed the pump out with a extra gasket,and also I always drill the bypass t at the tank out to increase flow back to the tank,This depends what type of gas system you have.When you start it close your valve on the bottom of your tank until the motor levels out then crack it enough to let the motor run free,this will help trouble shooting it

jimmy
 
Hello Jimmy,

Thanks a lot for this information! I will check my float to see if it has a hole in it. My carb doesn't have a drain/overflow towards the gas tank, is this normal? I will check and let you know!

Thanks again,
Rob
 
Hello FarmallCT,

Thanks a lot for your answer! I will check whether my float is filled with gas or not..
The carb of my F12 doesn't have an overflow drain towards the tank, is this normal? What happens with the extra gas that is not needed by the engine in this case?

Thanks again,
Rob
 
There must be a bypass on a F12,the pump pumps constantly the carb takes gas at different amounts.The extra gas must find its way back to the tank.Most people will disagree with me but a F12 gas system must be gravity feed,from the top of the tank to the carb.Rob,I should of asked,you are working on a F12 with a IH motor,not a flat head Waukesha
 
Rob,your bypass should be at the top of your tank,it is treaded into your tank,one line from the pump connects to it and a line from the carb goes to the end of it

jimmy
 
Yes Jimmy, my F12 has an IH motor. Actually, it is a German F12, called F12G over here. It seems like those German F12s have a fuel pump that is different from the American version. Maybe that allows that the bypass is not needed? I don't know that for sure, I will have to check. It seems like my F12 never had a bypass. The original gas tank is still on the tractor, and has no drain or hole at the top of the tank. :) Still wondering however, how they then could handle the excess supply of gas, though... I'll keep you updated on this!

Regards,
Rob
 
Rob, First off WELCOME! I would think your float is sticking or needle valve is not seating. Go back in carburetor and check it all out. oldiron29
 
Rob,a good friend of mine had the same problem with his F12,and someone hooked the carb straight up to the pump,we changed the lines to bypass and it ran like new

jimmy
 
Rob,

Is there any way to post a picture of yours and what it looks like so we can see how the fuel system is set up? It's been awhile since I saw a German F-12 so I cant remember if they should have it or not, though i'm pretty sure any of them with a fuel pump have some kind of passage to let extra fuel back in the tank.

~FarmallCT
 
Rob
I'm not familiar with your F12(G).

The attached link, however, might help you to diagnose your problem.
The carb in this pic is my Super A's.
Leakage may occur between the needle seat and the carb body.

Hope this helps.

Note: You will find a wealth of information on this forum. You'll be glad you found it!

Hendrik, from The Netherlands
Carburetor diagnosis
 
Thanks for the advice Jimmy! That also seems the most logical for me, as the excess supply of gas has to go somewhere. Otherwise, it would push the float down and the carb would flood again. I'll try some things out and I'll keep you updated!

Thanks again!
Rob
 
Hello,

Thanks again for your answer. I tried to upload a picture of my German parts manual in the Blog/Post gallery. I hope you can see it. This picture shows that the fuel line runs straight from the fuel pump towards the carb.. Seems strange, but it's also installed on my tractor in this way.. I don't quite understand what's done with the excess gas supply though?

Kind regards,
Rob
a212930.jpg
 
Jimmy, this is a picture of my German parts manual. I hope you can see it. This picture shows that the fuel line runs straight from the fuel pump towards the carb.. Seems strange to me, but in this way it's also installed on my F12. I don't quite understand what is done with the excess gas supply though..
a212931.jpg
 
Hallo Hendrik,

Erg bedankt voor je antwoord! Scheelt ook dat ik gewoon in het Nederlands kan communiceren met jou. :) Altijd handig voor in de toekomst. Het ziet er zeker een interessant forum uit, zeker als je de hoeveelheid antwoorden ziet die ik tot nu al gekregen heb!

Interessante foto in die link! Zo kan je inderdaad goed zien of de naald volledig afsluit en hoe hoog het benzineniveau dan staat. Bestaat er een algemene regel voor, voor hoe hoog het benzineniveau mag/moet komen totdat de naald volledig afsluit?

Wederom bedankt, erg fijn om van je te horen!
Groeten,
Rob
 
Hello oldiron29,

Thanks a lot for your reply! I will consider your advice! I will check my carb and keep you updated!

Thanks again,
Rob
 
The vent/return is threaded into the tank UNDER the hood, not on top of the tank. (Assuming its the same as it is over here, and there are 2 different setups for the F12 over here.
 
Rob dont worry about the excess gas. The way the fuel pump works is this when the cam pushes the fuel pump rod the rod isn't directly connected to the diaphragm. There is a lever and spring set up so that the movement of the rod compresses the spring that pushes up on the diaphragm. When the needlevalve lets the fuel into the carb the spring then can push the diaphragm up moving fuel. The rod in other words only resets the spring. If needle isnt open no fuel flows so no diaphragm movement spring stays loaded rod movement is wasted ,does nothing. Hope this helps. Have you turned the main jet screw in yet ? that main jet screw should be able to shut the fuel down and kill the engine
 
You are welcome! (Graag gedaan!)
Indien je wilt, kun je me een e-mail sturen door op de link rechts onder in dit tekstvak te klikken.
 
I also own a F12G here in the USA and the picture he has is right exactly like mine. There is no return line on the German tractors like the ones here. I would say either the float is to high or the float has a hole letting it fill with fuel or the needle valve is not seating right. The german tractor carb is real similar to ours and takes the same needle and seat and float but the pump is totally different.
 
Hello,

Thanks a lot for this information!! It's peculiar that the German tractors apply a different technique. :) Good to know that my German F12 doesn't need a return line, though. I will check my float level and the float itself. The seating and needle are new, so they should be OK.

Thanks again,
Rob
 
Great information, thanks! Special type of technique. :) I will check if my float and float level are ok. I set the position of the main jet screw like advised in the manual. But maybe that needs some more adjusting. Thanks for the advice on that, I will keep you updated!

Thanks again,
Rob
 
Welcome to the forum. Nobody seems to have noticed your impeccable English. Of course, if it is good grammar, why should anyone notice!
 
Hello Andy,

Thanks a lot! I'm doing the best I can to write some understandable English. Happy to hear that this is the case. :) Always good to know, as I will certainly use this
forum again! I got some great information so far.

Thanks again and kind regards,
Rob
 

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