Idle jet solved for F12/F14 carbs

I am getting close to sharing a solution for the idle jet on the F12/F14. Looks like the idle jet for the H/M will be the right solution, but I have a couple of more things to figure out. Hopefully by the end of the weekend, I'll have the specs and procedure to use the H/M jet.

I edited my previous post because I found an additional metering hole in an original part that I need to figure out.

WOO HOO, good job !!
I am sure this will help just about every F12, F14 owner !!
Even those who may be working on them in the future.

Ok, here is what I have so far.

The idle metering jet for a Farmall H/M will work, part # 49798D75, and has the same size orifice, and is the correct length. The top end of the metering jet should be 13/64" above the gasket surface on the lower part of the carb.

The #75 after the part number 24677D-75 is the drill size for the metering orifice. A #75 drill is 0.021 The thread size for the H/M jet is 5-40, and takes a #39 drill. Now, the hole in the carb is a whisker too large. So, you have 2 options. If the brass is really stuck in the base, you will be fine, just thread it in place like an insert. If the broken off tube comes out, you will need to apply either a VERY small bit of JB weld or Locktite to the threads on the jet. either should work fine depending upon your situation.

What I found was a small port in the side of a broken original jet that I was able to get my hands on. It is 3/16" below the carb base gasket surface, and from what I have been able to see in the cleaned out hole, there is a horizontal port in the carb base. I need to measure that hole in the tube to determine what size to drill. I suspect it is also a #75, but will know more when my #75 drill bit arrives. I don't have a pin gauge that small. IF you leave the original in place, it will be important that you drill out the top portion, and leave just the lower portion in the carb base. I'll try to get measurements on that soon. The small port in the side of the original tube could be oriented 360 degrees when installed, because the machined port in the carb base is larger than the tube.

So, long story short. you can replace your F12/F14 idle metering jet with one from an H/M, part number 49798D75. You will need a #39 drill bit, a 5-40 tap, and probably a #75 drill bit. If this all works out, I might consider making a few of these up if enough people are interested.

I'll update this post when I determine the size of that port in the jet tube.

My #75 drill bits showed up today and I can confirm that the port on the side of the idle jet is a #75 drill, or .021 The fit is not tight or sloppy. so while it may not be exact, I believe that using a #75 drill to create the port will be fine.

Also, my posting error. tube height above the bottom gasket surface is 13/32".

so now the ultimate test will be to actually do a carb with the Cub jet and one with the H jet and see what the results are.

In any case, I think either will work just fine.

I have purchased all the tooling to make exact reproduction of the idle jet. I should have the tooling within a week.

If I am successful in machining these, anyone interested if I can make a few extras?