Update on my rough running WD (again)...

Okay, so I've made some progress, but I'm not out of the woods yet. I took apart the carb and the gas valve and low and behold what did I find -- the gas valve was assembled backwards. Previous owner (???) or someone on down the line installed the plug in the out port and the 90 in the in port, so what was happening is that the fuel would come from the tank and bypass the sediment bowl and filter. Obviously it ran quite a few years this way, and I think the only saving grace is someone had apparently stuck a wire mesh filter up above the valve into the tank. So I replumbed the fittings and cleaned them out as best I could. Also cleaned the carb out, since I knew it had all sorts of sediment-style junk in it.



Put her back together for a trial run today but the gasket around the sediment bowl is shot. As soon as I fired up the tractor, the bowl started to weep around the glass and drip down onto the clutch. So I only ran it briefly. I picked up a new gasket and filter on my way home but haven't put them in yet.

The only downside is that even though the tractor did fire right up and run, it still seems to be running rough. Didn't have time to try and tune the carb adjustments though, so we'll see if that makes it any better, but I'm not very hopeful. What throttle position are you supposed to tune the main jet at? Seems like as soon as I crack the throttle open from idle, it starts to run rough, and putting it in gear to move it seems to make it choke and starve for a few seconds before it sputters back to life.

So whether or not this is the root cause of my problem or not, I am at least glad to have this issue that I didn't even know about fixed.

Some of the cobbling by previous owners of these old tractors is interesting. The idle circuit in the Zenith carb on my SC Case kept plugging until I put an automotive in line filter in the fuel line. Sediment screen was In perfect shape but I was still getting tiny junk in the carb. Hated to butcher it with the inline filter but it's worked flawlessly for me for the past 20 years or so. Jim

The fact that it idles good is a very good sign.
That means the compression is good, the other
problems can be overcome.

Before doing extensive carb tuning, be sure the
ignition is in proper order, especially the points
setting and the condition of the distributor
bushings and centrifugal weights.

The off idle stumble could be the idle adjustment
is too lean. With the engine idling, warmed up,
turn the idle mix screw in until the idle gets
rough, then back out so it smooths out, then turn
out another 1/8 turn or so.

The main needs to be adjusted under load. Hard to
do, requires some trial and error. You can use the
choke as a diagnostic tool. With the engine under
as heavy a sustained load as you can get, slightly
pull the choke. If the performance improves, it's
too lean, give it about 1/4 turn rich and try
again. If choking makes it worse or there is black
smoke, it's too rich, turn it a little leaner.

Thank you for the advice guys. I was going to try setting the carb today, but once I put my new sediment bowl gasket seal in and filled everything up and saw I had good flow at the carb (and no leaking), I fired up the tractor. It ran somewhat okay at idle, so I drove it around a bit, but it'd still starve off and such when first taking off in gear and it could barely pull itself up a hill. So I shut her down for lunch and came back out an hour later to tinker with her again. Mistake! I could barely get her to pop off again. It was weird, you'd pull the starter and let it spin for a bit, then let off... And as she spun down slower and slower, she'd occasionally catch and snap crackle pop for about 15-20 seconds then die. Nothing I could do would seem to overcome this. Then she wouldn't even crank over (vapor lock?), so I let her sit for another 30 minutes and finally got her to crank over and put her in the shed. Good grief, I'm scratching my head good on this one. Makes me feel like my carb float may be bad or I've got a serious air leak somewhere. Pulling out the choke when she'd start running rough just made it worse -- in fact I inadvertently killed the tractor a few times. By the end, I couldn't even run the old girl at idle, I'd always have to have the throttle cracked open for her to run. Oye.

I had the carb set at a basic starting point. Idle jet out 1 and 1/2 turns, and the main jet out 1 and 3/8 turns. I got a bit wild trying to set it later on, and had the main jet out another full turn and she seemed to hang on a bit longer but I still lost her.

fixerupper -- Yes indeed. I found quite a few places I expected cotter pins were just twisted pieces of baling wire.

Steve@Advance -- I only had one point when I was playing with it that it started to run rough and choppy and I opened the choke and it started to blow black smoke. Typically any other time I'd open the choke, the tractor would slowly starve itself and die.

Something tells me you have weak spark, or weak spark AND a carb problem. Weird things happen, as you well know. I just went through that situation with a tractor here at home. Gas tank outlet plugged, starving the carb, and the condenser gave out at about the same time. The condenser does this about every other year (thanks to the land of almost right) so I recognized it right away and replaced it. That solved the cutting out and banging. The plugged tank outlet wasn't as easy to solve. Jim

It just seems so arbitrary on whether or not it idles smooth or rough every time I go to start it, and whether it will run for 20 seconds or 5 minutes. So far I've got a list of culprits of the float needle valve and where it goes into for anything that can make it stick or not seal shut (and probably should double check my float for leaks?), weak spark (check condenser), and I am tempted to check the air flow to the carb since it seems to be running fuel rich as apply choke makes it worse not better.

In fact, I ran it again with the carb set at 1 and 1/2 turns out on both the main and idle jets, and just for fun while I had it idled all the way down (and running), I turned the idle jet in... Before long, I had the idle jet turned all the way in, and _nothing_ different happened. How does the idle jet work, exactly?