Farmall Cub

I am rebuilding an IH carb for my 1947 Cub. The very small tube, which is about 3 inches long, that extends from the top of the carb into the lower half has broken off of this carb and I do not have the missing tube. Is there a repair procedure for this and if so what is a replacement suggestion. What is the function of this tube?

yes it can be repaired. you will have to drill the old broken piece out. it is best to use a left hand drill bit. go to the search in the top right and enter how to repair broken idle tube. alsh check the how to section

Chet, The idle tube is part of the idle circuit. The calibrated end is the small piece (about 1/4" long) that screws into the carb top. In the past it has been said that the carb will function correctly with just that piece present. If you want to remove and replace it, I'd suggest spraying it for several days with PB Blaster or Kroil. Small left hand drill bits will sometimes cause it to unscrew. The threading is 4-48 in case you need to retap it. McDonald Carbs sells new idle tubes for around $10.00 ( I haven't ordered one recently).

Bob



From Steiner Tractor

What is broken is called the idle tube it controls the fuel when the carb is set at idle. The easiest way to remove it is with a left handed drill bit very carefully. The threads are a 4/48 that is not a standard thread. New tubes are available from Steiner and Case I/H.

I purchased the replacement idle tube from my local IH dealer and saved the shipping. He had them in stock.

Thanks for the info...... left hand drill bit! That's a new one on me, never heard of it. Do you run the drill motor in reverse to drill? Sounds like it?

Am I correct in searching for a #4 left handed drill bit? Is that the same thing as an EZ out?

You want to use 1/16" and 3/32" left hand drill bits (not an ez out) with a hand chuck. DO NOT use a drill motor, it will drill through the bottom of the carb and you will have this.

Chet, To add to what Bill said, the correct size bit for a 4-48 tap is a #42 drill bit which is .0935" in diameter. 1/16" = .06", 3/32" = .0937" which is almost the perfect size. The 1/16 and 3/32 will be much easier to find in left hand bits than a #42. Yes, you do run the bit counterclockwise.

Bob

Barnyard wrote:You want to use 1/16" and 3/32" left hand drill bits (not an ez out) with a hand chuck. DO NOT use a drill motor, it will drill through the bottom of the carb and you will have this.

Bill, I believe the tube is in the top half of the carburetor, not the bottom half.

Yeah, After posting that I got to thinking that was another project I had seen at a CubFest. Thanks! However, Chet, you still don't want to use a power drill on it.

Chet,

When drilling out the idle tube DO NOT USE A POWER DRILL. BTDT. You will put a hole where you do not want it.

Bill

Thanks to all you "Pros"......... now I will go marching "smartly" on.

Come on over to Sneads, FL on the 13th & 14th of this month and we can help you out.

I picked up a set of Left Handed Drill bits at Harbor Freight for $10
http://www.harborfreight.com/13-piece-l ... 95146.html