[Farmall] F-12 starting problems

Karl Olmstead kolmstead4 at msn.com
Tue Nov 10 20:01:26 PST 2009


I really wish I had a good answer to this question, but hard-starting F-12s are extremely common, and difficult to fix.  I have an O-12 which runs perfectly but won't hand start.  I tow it up a ramp.  It sharts immediately when I run it down the ramp and engage the clutch.  Runs flawlessly after that.  I have another O-12 that starts easily.  It's the prize of my collection, even though it's ugly.

I'm convinced that 90% of the starting problems on these tractors are related to the fuel system.  As I've ranted before, the decision to use a downdraft carburetor was one of IHC's bigger mistakes.

Go through the fuel system.  Make sure that the valve on the bottom of the tank works, and that fuel flows freely when it is open.  The fuel pump must work perfectly.  When you're hand cranking the engine, the fuel pump must fill the carburetor float bowl.  It might be worth building a device that screws into the float bowl drain and has a piece of vertical clear tubing, so that you can check fuel level in the float bowl.  It needs to be correct, which means that fuel pump is working and carb float and needle valve are in good shape and properly adjusted.

The rod that actuates the lever on the fuel pump must be the right length.  Seven inches, as I recall.  The camshaft lobe that runs the fuel pump must not be too badly worn.

The fuel pump, when working properly, puts out quite a bit of pressure.  The fuel recirculation system, which will be either a 'thingey' that sticks out of the hood in front of the fuel tank, or a T that lets excess fuel drain back into the fuel tank, must be in place and working.  Many F-12s have bypassed the recirculation system.  This would be more of a running than a starting problem, however.

I can send a copy of my F4 magneto rebuilding CD, but if the impulse is clicking and the engine runs, the magneto is probably in good shape.

As mentioned below, the carburetor must be in good condition.  That's a whole different topic, and one I'm still trying to understand.  There were so many different carburetors, and so many parts that got broken or lost during rebuilds.

You need to use the choke on an F-12 to get it started.  But if you crank the engine too long with the choke on, you'll flood the engine.  On an engine in good shape, two cranks and it's time to stop choking.

Most F-12 carburetors have a screw in the left side.  Removing that screw gives you a straight shot into the venturi area.  I use a can of carb or brake cleaner from Wal Mart, one with one of those tiny red tubes, to squirt cleaner into the carb just before I crank.  The engine will start without the screw installed, but it'll run roughly until you replace the screw.  On tractors where the fuel pump is weak, squirting flammable cleaner into the carb really helps.  I don't use ether (starting fluid); it can cause damage.

There; that's my list of F-12 starting tricks.  Much as I hate to admit it, the tow rope works better than anything else!

-Karl

--------------------------------------

> Date: Mon, 9 Nov 2009 11:27:26 -0600 (Central Standard Time)
> From: "H. L. Staples" <hlstaples at mcloudteleco.com>
> Subject: [Farmall] F-12
> To: <farmall at lists.antique-tractor.com>
> Message-ID: <4AF850FE.000009.03880 at DAD>
> Content-Type: Text/Plain;  charset="iso-8859-1"
> 
> This is a bit of a re-run, I sent a note the the AT list and am posting some
> of the replies.
> 
> A good friend has rebuilt one of these old girls.  No matter how much he
> Cranks it will not start. Just a little pull with another tractor and it
> Fires right up.
>  
> He says he can hear the impulse snapping but no start with the crank.
>  
> I know compression fuel and spark in the right order. At the right time.
>  
> Suggestions---
> 
> "Talk to Karl on the Farmall list. F-12s are difficult to get to start with
> The crank, often having fuel problems- worn end on the fuel pump drive, etc.
> 
> Guy Fay
> 
> "The plunger for the fuel pump is a good place to check. I ran into that
> Problem once on a F-12.  Sometimes the check valves on the pump can be quite
> Annoying as well.
>  
> My only other thought is you said it was just rebuilt. Is he positive
> Everything is put back together in time and working properly?"
>  
> John Hall
> 
> "H.L.:
> I would check the valves, of course.  However I had this problem many
> Many moons ago, The throttle shaft on the carburetor was loose in the
> Bearing.  In the kits they used to put a seal that pressed into the carb
> Housing and sealed the throttle shaft.  My old mentor mechanic
> Admonished me to no end for not installing that seal..  Put it in and it
> Started right up on the first crank."
>  
> Cecil in OKla
>  
> H. L. Staples
> McLoud, Oklahoma
> USA

 		 	   		  
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