TSX-241-B main needle seat

zuhnc

Member
Location
Macks Creek, MO
I have two TSX-241-B carburetors, one from each of my 8N's. The current in-service one is running rich, as evidenced by soot on the spark plugs. Jets were replaced per recommendations of JMOR, HOBO, and others. 0.032" idle jet, 0.046" main jet, and 0.046" economizer jet. Main nozzle has to be about 4 turns out to even get to run; at three turns out won't even start, much less run. The idle nozzle has limited effect on idle, most noticible between 0 and 1 turn out. (Yes, I know IN for rich and OUT for lean.)

I have disassembled both the in-service carb (we will call this one the "new" carb) and the not-so-clean one on the being-rebuilt 8N (we will call this one the "old" carb). I have noticed two differences, other than the jetting (not pertinent at this time). The pointy end of the main adjusting needle on the new carb is not as tapered as on the old. The second difference is, with the new carb, the needle goes into the little brass bushing at the bottom end all the way to the shoulder, and with the old carb, the needle stops about 90% of the way up the taper.

The question is: should the needle go all the way into the bushing, or should the taper seat on that bushing. Since the needle goes all the way up to the shoulder on the new carb, I think this is why that needle needs to be 4 turns out; at that point the taper is starting to control fuel flow.

Here are some images of the old and new needles, and close-ups of how the needle fits into the brass bushing.

Needle overall
20240722_152748.jpg

Tapered end
20240722_152929.jpg

Bushing in new carb
20240722_153045.jpg

Bushing in old carb
20240722_153107.jpg

Definite difference in size.

Needle in new carb bushing - needle goes into shoulder on straight portion
20240722_153411.jpg

Needle in old carb bushing - needle is still on taper prior to straight portion
20240722_153441.jpg

Close-up - needle in old carb bushing; seating on taper
20240722_153820.jpg

Close-up - needle in new carb bushing; seating on shoulder, straight portion inside bushing
20240722_153915.jpg

Any thoughts on correcting this? I can swap carburetors, but that still leaves the issue for the other tractor engine. zuhnc
 
I have two TSX-241-B carburetors, one from each of my 8N's. The current in-service one is running rich, as evidenced by soot on the spark plugs. Jets were replaced per recommendations of JMOR, HOBO, and others. 0.032" idle jet, 0.046" main jet, and 0.046" economizer jet. Main nozzle has to be about 4 turns out to even get to run; at three turns out won't even start, much less run. The idle nozzle has limited effect on idle, most noticible between 0 and 1 turn out. (Yes, I know IN for rich and OUT for lean.)

I have disassembled both the in-service carb (we will call this one the "new" carb) and the not-so-clean one on the being-rebuilt 8N (we will call this one the "old" carb). I have noticed two differences, other than the jetting (not pertinent at this time). The pointy end of the main adjusting needle on the new carb is not as tapered as on the old. The second difference is, with the new carb, the needle goes into the little brass bushing at the bottom end all the way to the shoulder, and with the old carb, the needle stops about 90% of the way up the taper.

The question is: should the needle go all the way into the bushing, or should the taper seat on that bushing. Since the needle goes all the way up to the shoulder on the new carb, I think this is why that needle needs to be 4 turns out; at that point the taper is starting to control fuel flow.

Here are some images of the old and new needles, and close-ups of how the needle fits into the brass bushing.

Needle overall
View attachment 79935

Tapered end
View attachment 79936

Bushing in new carb
View attachment 79937

Bushing in old carb
View attachment 79938

Definite difference in size.

Needle in new carb bushing - needle goes into shoulder on straight portion
View attachment 79939

Needle in old carb bushing - needle is still on taper prior to straight portion
View attachment 79940

Close-up - needle in old carb bushing; seating on taper
View attachment 79941

Close-up - needle in new carb bushing; seating on shoulder, straight portion inside bushing
View attachment 79942

Any thoughts on correcting this? I can swap carburetors, but that still leaves the issue for the other tractor engine. zuhnc
I have parts and pieces of those carbs laying around in my shop. By the way
 
Try the old needle in the new carb. If it goes in too far then you know the seat (bushing) has too big of a hole (not obvious from pictures) and the seat needs to be replaced (or carb). Needle should seat on the tapered part, not shoulder. You are correct when you say "I think this is why that needle needs to be 4 turns out; at that point the taper is starting to control fuel flow.".
 
The three needles I have are basically the same, other than the taper. Length to the shoulder is the same. All drop into the bushing on the new carburetor, and seat on the taper on the old carburetor. Picture 5 is the needle taper seating on the bushing in the old carburetor. Picture 6 shows the straight portion of the needle inside the bushing in the new carburetor. Might have to enlarge them to see clearly. Both of those images were taken with the cell phone through a borescope (from my old safe and vault servicing days!)

I have rebuilt the old carburetor with a new throttle shaft bushing (none originally, but I have a mill and the appropriate bushings), new choke shaft, and seals around the shafts. Reused the original jets (idle, main, and economizer). Installed on engine, and now have some control of fuel with the main needle. Have to increase the size of the idle jet; screw turned all the way in doesn't do much for the idle; no change in RPM from full out to full in. Should go from too lean (out) to too rich (in).

My only (not really!) issue now is fouling spark plugs. Using B6L (3112) NGK's, and if one fouls, it doesn't ever work again. I have not been successful in cleaning one. Seems the ceramic absorbs soot or oil and then the spark tracks over the ceramic instead of the tip/electrode as it should. Going to try either Autolite or Champion (or maybe both) next go round with the plugs.

Time now to get tools to pull that oversize bushing out of the carburetor and replace it. McMaster-Carr should have some brass tubing that is suitable. If not, I also have a mini-lathe to fabricate one, and plenty of brass stock. zuhnc
 

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