story of two carbs both IH

[oldiron29]

I had a 1955 cub that ran like cr:: Could keep it running on half choke was in it 4 time cleaning could not find the problem.
This carb had a broken idle tube and had been drilled out and retapped new tube install.
I removed a none good carb from another good running cub, While off took it apart and clean all before install on 55 cub.
The metering tube on 55 cub was open at the bottom and you could put a wire down the length and out the other end.
On the good running carb the metering tube was closed at the bottom end brass not dirt. This is the only thing I can find different.
metering jet, float setting, idle screw and needle and seat are all the same. So I am guessing the tube open on both end is wrong?
what say you? The 1955 runs great with the none good donor carb. Not sure if just changing part will get the bad carb working right?

[oldiron29]

sorry for the spelling Known not none. As in known good working carb

[Don McCombs]

No, it is not wrong. The discharge nozzle (what you called the metering tube), the main metering jet and the air bleed (non-removable) are a matched set for each of the different versions of the carburetor. You can use mis-matched components together. But, you may not get optimum performance.

[oldiron29]

Ok I should get the part name corrected. I must have mismatch part in the bad running carb.
so will a good rebuilt kit get matched parts for good running carb for cub?

[Don McCombs]

When you cleaned the carb, did you include the screen in the inlet coming from the sediment bowl?

[Bob McCarty]

The rebuild kits are basically "one size fits all". They are not based on the part# of the carb which tells you which bleed, discharge, and jet it should have. That being said, I've seen lots of carbs rebuilt with the same kit that seemed to run ok. After checking the inlet screen, you might measure the orifice of both jets and see if they are the same. Needing the choke to run normally means there is a fuel flow restriction somewhere in the system.

[inairam]

There are 4 major cub IH carbs part number families ( PN starts with a 2, 3, 4, or 63) and as Bob said the rebuild kits are one size fits all. Your 1955 I think should have a carb with a part number that starts with a "3".

[oldiron29]

I will look for the carb part # and post back. this not my first rodeo I have cleaned and rebuilt carbs form 1929 model A up through just about all of the IH letter series tractors. So simple things like screens and passages are always checked, carb cleaner, wire run through and compressed air blown out.

[oldiron29]

Carb part # is IH 355712 R91
I would like to rebuilt it so I have a good spare on the shelf.
I would need to know what the correct parts would be to put in it?

[Glen]

Hi,
Below is a page from the Cub service manual showing model numbers of IH carburetors, and some of the specs for the jets inside them.
The one on the right is a Zenith, so disregard that one.

http://www.farmallcub.info/manuals/gss- ... 002-02.jpg

The 251234R91 - R94 carbs were used through the years on Cubs, up to Cub serial number 192113,
I think, which was made in late 1955.
The maximum engine RPM was raised then, and other engine changes were made, Raymond Durban's database shows.
They started using carb number 364579R91 at 192113, I think.
It is the number my 1956 Cub has.

You didn't say the serial number of your 1955 Cub, if it is the older or newer.

They don't show the carb number you posted in the table above.

It says the spec sizes in the table above are drill sizes, for the IH carbs, so you can measure what you have.

The manual page above was made in the 1970's, so the info for engine maximum RPM is for engines newer than Cub serial number 192113.
The earlier Cubs were 1800 RPM max.

[oldiron29]

I am not original owner of this tractor so can't say if this is original carb either.
tractor serial # 198489 so this would be an early 57' not 55' and it no longer has the 355712 R91 carb on it, as my donor carb from another cub is working fine and I will leave it on. But would like to get the bad carb straighten out for future use on another cub.

[oldiron29]

Well guys i got my carb kit today and went right at it. Took the carb all apart and clean everything and ran wire through every passage.
Install new needle and seat and new float pin along with other parts. removed the idle tube as that is what I replaced last time around.
Found the idle tube had small open on threaded end like it was pinched, so I ran wire through and got it opened up as the other end was.
Not sure if it came that way or I over tighten it and damaged it? Put carb all back together and install it on a 1950 cub as i did not want to mess with the 57 because it runs good now with donor carb. Install my small starter gas tank as the hood was off this cub. Hit the starter and gave it just a little choke and it fired right up and ran good an idle good after open the air screw 1/4 turn idle sounds, have good full throttle.
No need for choke when running so what ever was wrong with this carb is no more. Very happy I was able to get it straightened out.

[Jim Becker]

. . . Found the idle tube had small open on threaded end like it was pinched, so I ran wire through and got it opened up as the other end was.
Not sure if it came that way or I over tighten it and damaged it? . . .

Came that way. I understand that the opening in the upper end of that tube should be 0.021".

[indy61]

Having to keep it running on half choke indicates a fuel restriction. The likely causes are partially clogged main jet, inlet screen at carb and outlet port at tank.
The idle tube should not matter. My Cub runs fine without one.

[oldiron29]

Yes I no the idle tube was not the lack of fuel problem I had, but it was the only thing I found to be an issue.
All mentioned screens and so on have been cleaned and were in place. The drain tube was not changed.
anyway all is good now. thank guys for all your help.