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Super C - Carter UT Carb Rebuild


wjohn

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I'm fixing up my girlfriend's SC. Supposedly the tractor was running decently and used with the Woods L306 mower up until about 1 year ago, when it suddenly died. That ended up being a broken distributor rotor button. Now I'm onto the Carter UT carb because after getting the ignition back into shape, the tractor ran like crap under load.

Upon disassembly I discovered that the bowl/body gasket had shrunk in from the sides and was shriveled up, and one of the screws was missing from the choke plate. Guessing that probably got sucked up into the engine. The choke shaft is also twisted/bent, presumably from someone yanking on the choke lever when the plate had slipped out of place and was binding up. Who knows how long ago the screw fell out. Most of the screws in this thing were barely tight. This is one of the versions with the cast iron upper half and aluminum lower half.

I know the consensus is generally to replace with a new Zenith. For $50 for a kit and free labor we figured it was worth gambling on this carb first. I untwisted the carb shaft as much as I dared and put the aluminum lower half of the body on a piece of sandpaper on a flat plate and sanded it down. The corners where the screws are were high and likely contributed to the gasket failure (you can see this by the shiny spots where I just started sanding in the first pic). It's much flatter now.

Any other things I need to watch out for when rebuilding one of these? This is my first time inside a Carter that isn't on a K-series Kohler.

SC Carb Before.jpeg

SC Carb After.jpeg

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@2+2 Guy rebuild my Carter UT for me about 9 years ago. We used a kit from TISCO. This spring I had to change the needle valve as it wasn't sealing. I got the new part from Mike's Carburetor Parts. They shipped it very quickly. I was very pleased that that it has a Viton tip, which works with modern gasoline. Here is the link to the rebuild kit from Mike's: https://www.carburetor-parts.com/ut-carburetor-rebuild-kit-k4429

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You will be fine ,trust us ,you can rebuild that carburetor , I took one look at it and it will be fine. 
 

I suggest you go to mikes carburetor for kits and advice . https://www.carburetor-parts.com/ihc-carburetor-rebuild-kits
also trust McDonald carburetor for parts kits and advice also.https://www.mcdonaldcarb.com/category_s/378.htm

your explanation tells me you must rebush the throttle shaft bore in the upper carburetor so it has minimum clearance for free rotation so to maintain maximum carburetor adjustment for maximum performance . Sounds  like this tractor has had a hard life. Things need to change for the better. 
ask more questions . 
 

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Thank you for the feedback. I had already ordered this kit from McDonald which showed up this week: UT Carb Kit

My only concern with this kit is that the picture on the website showed the conical Viton-tipped fuel inlet needle valve, and what I got is something I've never seen before. Anyone have any concerns with using this type of inlet valve (pic attached)?

I also included a picture of the slightly twisted choke shaft that I'm reusing. I was able to hunt down screws for the choke plate today at a hardware store.

SC Fuel Inlet.jpeg

SC Choke Shaft.jpeg

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Got it all put back together tonight. I did use the new inlet valve and throttle shaft. For some reason the screws and threads in the old throttle shaft were larger than the choke shaft screws, and the parts book says they should be the same. I'm guessing the throttle shaft I removed was already an aftermarket one, or someone drilled and tapped oversize. I also did some trimming on the gasket as it wasn't quite the right one.

I did put the choke plate in backwards on the first try, then fixed that.

We'll find out if this was successful this weekend.

SC Refurbed Carb.jpeg

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I got that needle and seat  for my super C from McDonald and it works great .

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Never met a Farmall c carburetor that could not be save. 
make sure the inlet screen is clean or replaced on the inlet fitting ,change screens on gas glass strainer and rubber gasket at tank ,more advice .

if you use gas with a lot of alcohol might want to change the float setting so it will close a bit sooner . 
 

also the new throttle butterfly shaft can’t have to inch  wobble wobble in it ,that means air will be pulled around the shaft ,changes the suction on fuel vaporizer , carburetor won’t perform well if to much leakage. I’m a a bit of a fanatic on this . My old C needs all the help it can get. We will machine shaft clearance to top plate to the minimum for free movements of shaft .0005 inch . 

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I put it back together yesterday. The tractor started fine, and ran fairly well, but the throttle shaft linkage from the governor wasn't letting it idle down. The bellcranks on the sides of the old and new throttle shafts were slightly different lengths so this wasn't totally unexpected. I followed the procedure of placing the speed control lever in the full speed position and then adjusting the yoke on the linkage to line up with the governor arm and with a fully opened throttle plate. Then it idled great and I took it out into the pasture to put it under load.

I set it to full speed with the throttle/speed control lever, and it did the same thing it was doing before the carb rebuild - runs like crap at full speed, bouncing RPM up and down a little very rapidly.

If I manually operate the throttle shaft bellcrank with my hand, it goes to higher RPM just fine and sounds great. Let go and try to let the governor control the throttle shaft, and it does that rapid fire bounce bounce bounce of the RPM. I'd describe it as a slightly slower machine gun rate of fire - still very fast. At that point I figured it was probably the governor and called it a night. I'll dig into the book to look up all of the adjustments to try first, but I'm bracing myself for taking governor parts out of the front of the engine. The carb did need to be gone through so I don't regret doing that - it just wasn't the main issue.

We also replaced the alternator as it would squeal for 10-15 seconds after startup. The new one spins great now and per the gauge is charging properly. It's a couple steps forward and then you find out there are still more steps to get to the top! It's a pretty good looking old tractor.

SC Overall.jpeg

SC Carb Linkage.jpeg

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Does governor resist you if you try to change the carburetor rod speed by hand?

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26 minutes ago, 560Dennis said:

Does governor resist you if you try to change the carburetor rod speed by hand?

It does - you have to fight it just a little bit. And it will pull it back to low idle no problem when you either move the speed control lever down to slow, or if you manually rotate the throttle shaft to rev it up when the governor is set to low idle. It's not like it's completely blown up inside... I know it's highly unlikely it's skipping teeth or something, but that's almost how I would describe it. Like the governor mechanism is trying to keep it at full speed, but slips/skips trying to do so and keeps trying over and over again.

Thanks for all of your help so far, by the way!

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Couple of things

Does the fan hub have the screw in the side that you fill half way with oil ? -- my want to check the oil level
not sure what year they went to the sealed bearings in the fan hub

Back the bumper spring adjuster screw out -- remove it to check the spring condition -- the spring can get gummed up or rust

Did you set the carb linkage with the throttle in the high speed position - so that the pin just slips in the linkage ?
adjusting the WOT position of the carb and governor

then turn the bumper spring back in to "settle" the governor action

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18 hours ago, HydroTek said:

Couple of things

Does the fan hub have the screw in the side that you fill half way with oil ? -- my want to check the oil level
not sure what year they went to the sealed bearings in the fan hub

Back the bumper spring adjuster screw out -- remove it to check the spring condition -- the spring can get gummed up or rust

Did you set the carb linkage with the throttle in the high speed position - so that the pin just slips in the linkage ?
adjusting the WOT position of the carb and governor

then turn the bumper spring back in to "settle" the governor action

I will have to look for that on the fan hub next time I'm out there, thanks.

Noted on the bumper screw. I had been finding that as a fairly common issue when searching online - sometimes all rusted up, or even broken. I'd love it if it was that easy but I won't hold my breath.

That is exactly how I readjusted the governor/throttle linkage. After changing throttle shafts, it wouldn't low idle. I could even tell where the yoke and jam nut used to be on that shaft because there wasn't any paint, so someone had to have adjusted it when they put that previous throttle shaft in. This adjustment moved it back to where it was covering the unpainted portion of the threads, so everything is lining up there.

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  • 4 weeks later...

So this has been interesting. I messed around with the bumper spring and got rid of the surging. It looked to be intact and functioning when I removed it for inspection. Went back into the pasture to mow some taller grass and it still wasn't running great under load.

I swapped out the condenser with a new spare, tightened the points gap slightly, and swapped in a coil from another tractor. I also adjusted the valve clearances. It ran better, but still didn't sound right at full load. I strongly suspected the ignition timing at this point.

Checked the timing with a decent light I bought a couple years back. I think there may have been a pointer in the flywheel (referenced in the manuals but not very clearly) that is missing. I am fairly certain that #1 piston at TDC is with the "1-4 DC" mark on the flywheel pointing straight down, which lines up with a stiffening rib in the metal cover in front of the flywheel. I verified that the #1 and #4 pistons were at TDC by looking through the spark plug holes. Started the engine up and the timing was 55 degrees advanced! I adjusted the distributor to get it down to 15 30 degrees at high idle per the data in the I & T manual, and under load it sounds like I think a tractor should. (Make sure you read the fine print in the I & T manual - for some silly reason you have to double the numbers in the table to get the actual degrees advance and RPM at the flywheel! I initially messed this up).

I'm not sure how the timing could have jumped 40 degrees. I can only guess that the tractor has been like this the entire time this family has owned it (maybe 15 years?) and they just never realized it. I'm still not 100% sure what caused it to all of a sudden run like garbage under load, so I'm holding my breath a little, but maybe the coil or condenser were on their way out. The governor is maybe a bit too sensitive but I can tweak that down later. It runs well under load.

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On 8/13/2023 at 10:34 PM, wjohn said:

Started the engine up and the timing was 55 degrees advanced!

I had that happen to me several years ago, on my 300. The guy I bought it from hauled it up to me, and we unloaded it and it ran fine. Took it out to work it later that day, backfired and died. Come to find out, the distributor bolts had come loose and let the distributor turn to the point it wouldn't run. Retimed it and it runs fine now. I also had a similar problem with my Cub having no power; did all the things that you said, and still couldn't get it nailed down. Then I put in an electronic ignition module and that solved the problem. You might try that if the problem comes back. 

Mac

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12 hours ago, MacAR said:

I had that happen to me several years ago, on my 300. The guy I bought it from hauled it up to me, and we unloaded it and it ran fine. Took it out to work it later that day, backfired and died. Come to find out, the distributor bolts had come loose and let the distributor turn to the point it wouldn't run. Retimed it and it runs fine now. I also had a similar problem with my Cub having no power; did all the things that you said, and still couldn't get it nailed down. Then I put in an electronic ignition module and that solved the problem. You might try that if the problem comes back. 

Mac

Interesting. The inner distributor bolt was loose, but the outer was rock solid so I hadn't figured that would've let it move... but who knows as I didn't try to wiggle the distributor first before loosening that bolt. I'm not a Farmall guy by background but thanks to this forum I can get answers to my obscure questions! Fingers crossed the SC is good now.

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