Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 9:32 am

The carburetor for my IH Cub (1948) is in need of a rebuild. Before ordering any parts I disassembled it. I took apart the top and bottom halves. Then while attempting to remove the stuck idle mixture adjusting needle I grasped the unit incorrectly and ended up breaking off the Idle Jet, that long skinny tube.

Am I dead in the water or can I get the idle jet out and replace it? I do notice that on the top of the throttle body there appears to be a pin head that could be the other end of the idle jet. Do I just tap it out from the bottom or is it time for a new carburetor?
Thanks!

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 10:01 am

The broken idle tube can be removed. I'd start by spraying both halves with a penetrating oil for a day or two. The threads for the idle tube are 4-48 which you probably won't have available unless you order one. I don't have a chart in front of me, but left hand drill bits that are smaller than the drill size for a 4-48 tap will sometimes unscrew the 1/4" threaded end in the top. If not, then it would need to be drilled out and chased. If you're lucky, the longer broken piece in the bottom will pull out with some fine tipped vice grips or the left handed bits. If you're uncomfortable doing it, you can mail it to me and I'll remove the broken pieces for you.

Bob

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 10:10 am

Assuming that your tractor has the IH carburetor, the broken part is 251 331 R1, Idle tube. I would not call it the idle jet. It serves to supply fuel to the idle circuit of the carburetor. The threads are 4-48-- not one of the most frequently encountered sizes. A #42 drill is preferred, but a 3/32 drill is slightly larger than the recommended tap drill. Any wobbling with the 3/32 could damage the threads. Do not dill too deep nor rethread too deep. Remove the idle mixture screw and blow out all chips after drilling and tapping.
If this is your first experience with tapping, better engage the services of one who has experience-- and watch while they do it.

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 2:49 pm

Thank you to Bob and Bus Driver for the replies.

I am not sure if I understand the suggestions, though.
To clarify what I said, the idle tube is broken off right at the base with nothing remaining to grip on to.
I will try to put some photos here.

Am I to understand that the idle tube has an upper portion that has a 1/4" thread and a lower narrow portion that has about a .0935" diameter thread? Or are those two different parts? (see photos).

Are you suggesting that I drill out the narrow end with a number #42 drill (to what depth?) and then carefully chase it with a 4-48 tap to remove any remnants of the tube. Then screw in a new tube?

Or would putting a reverse drill in the upper portion and then twisting it out with an inserted screw be the way to go? I would prefer to try this myself although as a last resort I would take Bob up on his offer. I also have a machinist (retired) friend who I may consult tomorrow.

http://www.flickr.com/photos/kb1awv/13877936974/in/photostream/

http://www.flickr.com/photos/kb1awv/13877543825/in/photostream/

https://www.flickr.com/photos/kb1awv/13877543285/

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 3:20 pm

In your second photo, the little remaining stub is the 1/4" long 4-48 threaded piece. The other two inches is unthreaded and I was thinking that it broke off in the bottom half of the carb body. If that is not the case, then you just need to remove the short threaded end. Left hand drill bits will often catch and unscrew the broken piece. Do this by hand and not with an electric drill. If it doesn't come out that way, then you'll need to drill to the proper size and chase with the 4-48 tap.

Bob

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 3:41 pm

Sounds good, Bob!
I think I can handle that. I'll get myself over to the Home Depot tomorrow to get the tools.

Thanks again.

Ken Carr

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 4:20 pm

You're not likely to find either the left hand bit or tap at Home Depot. If you have a GOOD local hardware store you can try them. Otherwise consider McMaster-Carr. http://www.mcmaster.com

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 5:30 pm

Thanks Don. My local hardware store usually doesn't have odd stuff....we are out in the sticks. I'm going north to the bigger city tomorrow. I do know a good hardware store there. Then I wonder if NAPA has it? We have a great NAPA here in town.

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 5:55 pm

Don McCombs wrote:You're not likely to find either the left hand bit or tap at Home Depot. If you have a GOOD local hardware store you can try them. Otherwise consider McMaster-Carr. http://www.mcmaster.com

I got my 3/32" left hand bit at NAPA. Don't yet own the 4-48 tap. I've done 3 or 4 and have yet to need the tap. Use a hand drill to control the bit if you have one. If not remove the chuck from your drill and hand control it. The broken stub will usually just back out whole or in pieces and you can pick out the residual with a dental pick.

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 6:48 pm

Thanks, Denny. It's off to NAPA tomorrow. Our small town store is really great. They even have stuff like oil filters for my '41 Buick. Real friendly bunch. (Wyoming, RI - in town of Richmond)

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 15, 2014 7:40 pm

I know a lot of people don't like easyouts, and for the most part, neither do I, BUT I have had success with a very small one to remove the upper part of the tube. If you try this, just don't get too agressive because if you break it in the tube, you have just greatly increased your problem and maybe even eleminated the chance of removing it alltogether. Also the lower part of the tube is just extended into the lower portion of the carb. Stan

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 29, 2014 4:34 pm

Success, maybe.
I drilled out the throttle tube with a 1/16" left hand drill just to get things started. I ended with the 3/32" left hand drill. Most of the original threads of the casting are showing. There is still a little bit of brass.

I will order a kit and then attempt to screw in the throttle tube. If it doesn't go I will drill a bit more. Hopefully that will do it. Otherwise I will have to go the tap and die route. Looking good, though.
Thanks all for the help!

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 29, 2014 6:21 pm

Roadmaster71 wrote:Success, maybe.
I drilled out the throttle tube with a 1/16" left hand drill just to get things started. I ended with the 3/32" left hand drill. Most of the original threads of the casting are showing. There is still a little bit of brass.

I will order a kit and then attempt to screw in the throttle tube. If it doesn't go I will drill a bit more. Hopefully that will do it. Otherwise I will have to go the tap and die route. Looking good, though.
Thanks all for the help!

After using a 3/32" bit I wouldn't drill any more. Find something like a dental pick and pick out the little pieces of brass from the threads.

Re: Carburetor Idle Jet - possible to extract broken one?

Tue Apr 29, 2014 7:04 pm

I agree with Denny. DO NOT drill any more. Get yourself the proper 4-48 tap to finish the job or risk a much more difficult repair job.