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IH Carb Inlet Threads

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Don B.
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IH Carb Inlet Threads

Postby Don B. » Tue May 16, 2017 6:56 am

So when I bought my '48 Cub in pieces, the carb was literally just handed to me. There was no fitting in the inlet. It looked to be in decent shape so I cleaned it up, put a kit in it and set it aside. A couple days ago, I went to put on the fuel line and realized the inlet threads were way too big for the compression fitting. Turns out they are 9/16-18 rather than the 1/2-20. :? I suppose they were changed at some point but they must have done a good job because you can't tell.
So far I have not found a fitting that will connect the 9/16-18 inlet to the 5/16 steel tubing.
Does anybody know of a source or another option?
Thanks.
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Don B.
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Re: IH Carb Inlet Threads

Postby Don B. » Tue May 16, 2017 7:11 am

Would this fitting be the easiest fix?
Hopefully, the text is readable.
fitting.PNG
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Re: IH Carb Inlet Threads

Postby Slim140 » Tue May 16, 2017 7:15 am

I would say they are 1/4"-18 pipe thread, that puts you close to 9/16". Depends on what tap was used rather they are straight or tapered though. If a tapered tap was used you have to grind the end of the tap off to get better threads because the hole isn't deep enough, I have a ground off tap :) You have to take about 3/8"-1/2" off the tap if it's tapered. Here's the tap, a new one on the left and ground one on the right.
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Re: IH Carb Inlet Threads

Postby Gary Dotson » Tue May 16, 2017 7:28 am

Don, I have to agree with Chipmaker. I've seen a lot of Cub carbs, where a 1/4" pipe fitting has been cobbled into the inlet, usually because the owner did not know the difference. If it's trully 9/16 x 18, you should have little problem finding a brake line nut that will thread in. It will be either 3/16" or 1/4" tube and could be drilled & champfered to fit your 5/16" line. I'll look to see if I have one.

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Re: IH Carb Inlet Threads

Postby Ken (48 Cub) » Tue May 16, 2017 8:21 am

Usually they are boogered up by screwing a fitting made for a rubber gas line, mine was. Helicoil it.
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Re: IH Carb Inlet Threads

Postby Don B. » Tue May 16, 2017 8:45 am

I'm curious. If it was changed to the 1/4-18 pipe thread, why not stay with it?
I suppose there is a reason.
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Re: IH Carb Inlet Threads

Postby Slim140 » Tue May 16, 2017 9:00 am

Don B. wrote:I'm curious. If it was changed to the 1/4-18 pipe thread, why not stay with it?
I suppose there is a reason.

Both of mine have been converted to 1/4"-18 pipe thread and I've had no problems with them. Whoever owned them before me tapped them that size, I only cleaned them up and sealed them good. I don't care what size thread is in mine as long as it doesn't leak :D
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Re: IH Carb Inlet Threads

Postby staninlowerAL » Tue May 16, 2017 9:24 am

Agree with Chipmaker. If the 1/4" pipe fits well, a 5/16 compression x 1/4 pipe adapter fitting can be installed with sealer and you're back to the correct size steel line with a ferrule. Makes it easier to remove the line later without having to deal with the possibility of cross-threading into the soft metal of the carb.
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Re: IH Carb Inlet Threads

Postby Don B. » Tue May 16, 2017 12:21 pm

Alright, the threads are, in fact, straight 9/16-18 size. Definitely not a pipe thread even though I had convinced myself that they must be.
So now my plan is to take a brake line fitting which matches the threads and modify it. The closest brake fitting that NAPA had included a short piece of 1/4 inch flared tubing. I will remove the tubing and drill it to 5/16. Then I will "countersink" the end so it can receive the 5/16 ferrule.
Although I am no Chipmaker, I think I can make that work. :|
I will let you know what happens.
Thanks.
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Re: IH Carb Inlet Threads

Postby Bob McCarty » Tue May 16, 2017 4:17 pm

If the fitting looks the same as the 1/2-20, you can probably just cut the flare off, enlarge the hole and use a 5/16" ferrule that seats inside the carb inlet. I don't think you need to countersink anything unless I'm misunderstanding what you have....
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Re: IH Carb Inlet Threads

Postby Matt Kirsch » Wed May 17, 2017 2:31 pm

I think I used a double-ended compression fitting to fix mine. Take the nut and ferrule off one end and it had 9/16-18 straight threads as I recall. The threads were pretty much gone so I ended up JB Welding the fitting into the carburetor.

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Don B.
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Re: IH Carb Inlet Threads

Postby Don B. » Tue Feb 05, 2019 4:04 pm

I guess I never followed up with my fix.
the threads are, in fact, straight 9/16-18 size. Definitely not a pipe thread even though I had convinced myself that they must be.
So now my plan is to take a brake line fitting which matches the threads and modify it. The closest brake fitting that NAPA had included a short piece of 1/4 inch flared tubing. I will remove the tubing and drill it to 5/16. Then I will "countersink" the end so it can receive the 5/16 ferrule.

One NAPA store was overthinking it and I didn't get any where with them. While travelling an hour away on business, I stopped at another NAPA and they had me come into the back and find whatever I thought would work. The small "countersink" in the end of the drilled out fitting was really just to put a nicer surface in contact with the ferrule. Worked great. No leaks. The only problem will be when I completely forget everything I did and try to switch carbs with another tractor. I have to remember that the carb and the fuel line are a matched set. :)
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Re: IH Carb Inlet Threads

Postby xraycajun » Tue Feb 05, 2019 4:24 pm

Could you post a picture of that setup? That would go a long way in helping me get to the right part, if it's not to much trouble. Thanks!

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Don B.
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Re: IH Carb Inlet Threads

Postby Don B. » Tue Feb 05, 2019 5:43 pm

I don't have a great picture of the fitting. I need to take some.
20190205_173610.jpg
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Re: IH Carb Inlet Threads

Postby Bob McCarty » Tue Feb 05, 2019 8:02 pm

If the 1/4" NPT fitting is leaking, and you don't want to helicoil it, you can JB Weld an Edlemann 168540 fitting into the inlet. You'll have to cut off the existing ferrule, place the female nut on the gas line and then add a new ferrule. I've used this where the opening was already too big for the helicoil to work. The down side is that you can't remove the inlet screen and the carb isn't interchangeable on a Cub with an OEM setup.
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