362173r91 carb

I got the carb number off the carb that i was having trouble with the idle air screw being effective. it is 362173r91. It"s on our 400 gas.
Could someone tell me more about that carb? what should have been done to it to make it a r92 as mentioned earlier (difference in r91 and 92)? should i bother with the upgrade if it has not been updated?
what should the idle air screw look like? someone said the gas had a different taper from the older but more commonly found kerosene carb screws.




thanks in advance for the info. will be away over the weekend but will check back, and check email and eventually get back to tractor. i do plan on total disassembly and thorough cleaning, but want to get it right. Carb is mechanically like new, there has to be just one detail wrong--junk in a small port, wrong screw, or float/main jet relationship not stock are my guesses.

Rich idle and poor start were reason for dissasmbly first time. (found one side of float was 1/16th inch high, set both to 1-5/16 and governor was way out of sync!)


karl f
ps to clarify from last time the only changes in idle quality are when creating a leak.

IH made enough changeover kits to change all tractors sold with R91 over to R92 in early 55 I think. All evidently didn't get changed because a new changeover kit shows up once in a while. Even if you have a R91 it should run and idle okay. Changes were in size of main seat or jet, discharge jet and a high speed ajusting screw and nut was added. Also a passage was pluged in bowl. Your carburetor has some change added. R 91 ones came with a plug were you have a high speed adjusting screw. The correct idle adjusting screw has a straight round section about 2/3 to half the thread size for a short distance on end then a taper to point. Main seat for a R92 carb has a .051 hole size. Main discharge jet has all three holes .055 size and tip size is .136 .

You need to inspect this carb to properly ID a "Triple Port" carb. They are different from your typical 300-450 carbs, they have an extra fuel passage to help fuel delivery and keep a high quality idle at the same time. Best of my knowledge, they were only made from January 1955, thru July of 1955. There is a stamped date code, in the gasket surface of the carb flange, but have not seen theis on carbs that were older than 1949 on the M-450 carbs that Ive been into.

Only reason I belive this style of carb existed back then,, was for a gasoline conversion,, for when someone wanted to take an LP tractor and convert it to gasoline and still use the LP engine componets. The carb requirements to deliver fuel, kind of exceeded the stock design to do that kind of conversion without suffering idle quality.

To ID a triple port, your looking for the location of the third passage in the 300-450 style throttle body. When you look at the throttle body upside down, (float and needle removed) your looking at the holes that are right behind the float,, close up by the venturi bore,, not inside the venturi bore, on the outside, where they have acces to the fuel bowl,,,, On the plain jane 300-450 carbs wit the R92 part number,,, you will only see 4 holes for passages. If you see 5, you have a triple port carb.

Follow this passage up into the throttle body,, you will find, it exits right below the throttle butterfly, and only gives fuel when the throttle plate is more than half open. It operates by throttle position,,, when vacuum hits that passage, it draws fuel right out of the bowl, up, into the passage and exits above the venturi, but right below the throttle plate.

I have seen R92 carbs with the hole below the throttle plate, and the passage from the bowl plugged by a brass plug, or the passage not drilled, or completed, but the top exit hole was installed, for if any reason someone wanted to convert the R92 carb into a R91 style carb.

Info on the typical 300-450 carbs, they are twin port carbs. Here is what they did,,,, this goes back to the M, which is a single port. This means, the carb has only one passage (besides the idle circuits) to deliver fuel, in the M, it was thru the main jet and metering stem, and during a certain postion of the throttle plate,, the idle passage has a circuit that does pull fuel right out the bowl too,,,,, but that circuit exists in most of these carbs, and is not tunable unless you really get into the carb, and know what your doing. When the 300 and 400 was built,,, they changed the carbs internal passages, and created a second port,,, or they redesigned the passage mentioned abou the M idle passage,,, either way, they gave the idle circuit its own exit passage way up high above the venturi,, but they kept the location of the secondary passage, pretty much the same location as the M carbs idle passage. Still operated off the throttle position, but routed entirely different,, either way, fuel delivery now had 2 ways of fuel delivery,,,,, other than the regular main jet/metering stem single delivery.
Hope this helps,,, Id go cleaning on that carb you have,,,,, a tiny set of drill bits help clean,,,, a passage Ive found thats blocked when the idle is acting up,, is located when you remove the tiny brass idle tube in the bowl,,, once that stem is removed, run a tiny drill bit down the hole,, it sould go deep to the main jet,,, dont drill, just see if anything comes out,,, you might find it plugged in tat location,,, and it will make for bad and erratic idle condtions. Need help, call me. 574-893-7437, or email [email protected] ChadS The Tractor Shop.com

think the screw is wrong, i believe it tapers all the way to the thread. will look again though next time i'm home.

thanks
karl f

there seemed to be an extra dummy hole next to the idle jet and the other hole, similar sized. Looked like a well made plug or undrilled casting. There were passages sideways but the straight up one was definitely blocked.

I may buy a digital camera just because of this!

the tractor has z casting codes in many places.

when i tear into it again i'll ask more questions.

karl f

Idle air screw end has very little area before taper starts then a long taper, around 3/8 inch long from threads to end of taper. You probably have the right one, I think the ones with idle air adjusting screw lower on carb have a bigger thread. In the earlier post I mentioned 2 holes in throat above venturi area for a R92. Since you have a R91 you have another hole. If your carb was changed sometime to a R92, and if you look at the 2 holes in throttle body that match the idle jet and air bleed there is two holes to one side of those holes and one on other side. If it was changed the hole close to the 2 middle holes on side with 2 holes will have the passage plugged. Change over kits had a new ID tag that was supposed to be installed on carburetors when changed. My experientce on working tractors is the R91 had more zip in some RPM ranges than a R92 and the R92 was better in other RPM conditions. One IH bulliten indicated the changes to R92 were made to try and help fuel use. Although Parts books don"t show it I"m pretty sure a R93 was sold sometime, but never had one apart.