Couple days ago while warming up in the cold it never started firing on all four. It would usually spark and putter a bit while choked then finally purr on all four after 10 or so seconds. But it never did that.

I've since:

1)pulled and sprayed nearly a whole can of carb cleaner in every hole in the carb. 

2) cleaned the bowl, and filled with fresh new gas (it was nearing empty when it started doing this so I thought maybe some gunk I hadn't gotten out had clogged the carb)

3)Seafoamed the valve train and changed oil.

4)Pulled and cleaned suspect plug (#4? the one by the steering wheel). It was oily, but, that was also after a week running on 3 cylinders so I didn't think too much. 

5) Let it run at max RPM and at low RPM and while pulling a small load moving snow, for various amounts of time each. 

6) Cleaned and sandpapered the rotor, cap and points. 

It is very clearly only #4 that is not firing, and sometimes it sounds like it might be. It is getting spark, and the other cylinders are clearly getting gas. Pulling a wire from them while it's running it's clear they're running fine.

My question is: Is valvetrain/compression my only next option? I'm not very good with the governor or points ignition. Could there be an issue with either of those? Would points/condenser only affect one piston? 

I suppose I could try and flip the cap around and see if #1 starts having the issue. I DID NOT adjust valve lash at the beginning of last year when I was doing the tune up. I didn't want to ruin what was already running good. It has good strong spark - felt through my winter leather gloves and the plug wire. Probably a good 1/8"-1/4" clear white light spark. When it's warmed up the carb is tuned right as I can tell any adjustments or choking cause it to stall or run weirder. 

Thank you guys in advance for any ideas to try next. I have a feeling it's a weak spring, but I wanted ideas before I go flounder about. 

Might want to look at plug itself, New plugs can be bad too.   or plug wire... or a wet streak or crabon or oil in the cap...

 Caps don't turn 180 degree, one way only.

JC-WI wrote: Might want to look at plug itself, New plugs can be bad too.   or plug wire... or a wet streak or crabon or oil in the cap...  Caps don't turn 180 degree, one way only.

Let this be a warning to those that, like me, struggle with acute onset of dumbness on occasion. Check for spark THROUGH the plug, not just to the plug. 

I feel like a leach on this forum, always with dumb questions I'm bouncing around, never helpful. 

Thanks Doc! I don't know why I wouldn't have tested compression when I had the plugs out, but I don't remember specifically doing it. So Probably was just lazy at the time. 

1)  swap sparkplug. if #4 still doesn't fire....

2) swap sparkplug wire, if #4 still doesn't fire

3) buy NEW distributor cap and install.

MadCow wrote: ...Would points/condenser only affect one piston?...

Rarely.

It is possible for the distributor cam or the shaft bushing to be worn unevenly enough to cause the points to not open correctly.

Glad you got it running

Madcow, got a story to tell you about sparkplugs, actually have a few.

1.  My uncle had a bought a 1968 Chevrolet Impala brand new and drove it for 60,000 miles before he had the local dealer do a complete tune up. He went to picked up the car and it was gutless. Called the dealer up and told him the car was coming back in because it wasn't running good. The dealer tried passing it off that it was all right. Uncle told him he was stopping the check. The dealer had him bring the car in and my uncle was irrate at the fact the car had AC plugs from factory and they put Champions in it.  Then made them run a pressure check on the spark plug testor and found 3 of the 8 plugs would not fire when they got up under pressure. The dealer was going to put in 3 new champions and Uncle said NO. you put in AC plugs like you took out. and check them before putting in. The dealer finally agreed and sent the mechanic after the AC plugs. The new AC plugs were checked and none of them failed and my Uncle drove that car for years and then my nephew bought it and drove it to near 200,000 miles.

 2.  I was going to a auto tech school at the time and stopped at the parts store and bought new plugs, points, condenser and rotor for our D17. It was spring time and dad had started plowing. Must have been a sat. or Sunday when I did the tune up, because otherwise I would have still been at Pine Tech. Dad had come in from plowing at noon to gas up and get a bite to eat and I had a few minutes and did a 'tune-up' on the tractor, even using a timing light instead of tune by ear. lol  Well, he went back out and I figured I wouldn't be seeing him until after dark or he was done. He was back in one round and was he mad. Had some words like, 'What the HELL did you do to the tractor it runs like CRAP !!!!'  I told him I put in new champion plugs, points, condenser, rotor and tuned it. He gruffly said, "put the old plugs back in" and I did. He left and didn't come back until after dark.  He stopped at the barn to see how far along I was with chores and I asked him 'how did it go?' and he replied "Got the field plowed. ".

3. Third story.. Neighbor bought a D17 with a loader on it. You could here that tractor missing and barking when pushing snow out of his place. He broke his loader and called to see if I would weld it. Said I would and when he got here, I said 'lets see if we can get your tractor to run right first'.  Blew the engine off to get as much of the grease and oil gone, then I pulled the dist cap and plug wires off and took out the plugs and clean the points and reset the gap and put the cap back on. Noticed the air cleaner was plugged, took that off and shook gas around in it and blow it with the air hose. Then took off the valve cover, gasket was inside, washed the gasket and cover, set the valves and put the cover on. Found a new set of AC plugs for it and put them in, and put air cleaner back on with new oil. Told Bill that it was time to see how it would run and he started it. Music to the ears running on all four and no more oil coming out from under the cover and no smoke out of the exhaust. Handed Bill the champ plugs and told him to throw them or bury 'em, just don't keep them. Then we went and welded up his loader.

He later said he never thought that tractor would ever run or sound so good.

OK, Nuff of them past memories.

90% of the time, carb/fuel issues are actually ignition related. Get a good, strong and well timed spark FIRST off & tune the rest of the engine around that and you won't go far wrong.

Swap the plug and see if it moves.  Just went through that with my D17.  Good spark and compression, valve train good, no manifold leaks.  Swapped the dead hole plug to another hole and the dead hole moved.  4 new plugs and she's good to go.

AaronSEIA

Mike,  You were just lucky. You got 4 that worked........ 

Steve@B&B

Yup.

So naturally, it's the LAST thing I do

HudCo wrote: seams like everyother gas tractor that comes here that runs crappy is a valve issue bent push rod stuck valve no lash .          brought a cute little 404 farmall home saturday for the neighbor it ran crappy had a bent push rod and a stuck valve he got the valve working and he straightened the push rod now it sounds and runs good

I opened up two locked-up B-125 power units this winter; both had a stuck valve and a bent pushrod.

The redneck B started running a little bit crappy the other week, compression felt uneven on the crank so went back into the valvetrain expecting to see one of my fabricobbled rockers or pushrods had failed. Turns out a few of the valve clearances had closed up as the valves bedded back in/knocked crud off the seats & just setting the overhead sorted it. Some of the valves had "negative" lash at that point, surprising how much crap can build up over years sitting, I even had them set loose (.060") to begin with to account for this!

Amazing how they even sealed enough to run in the first place, thing runs great now!