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skeeter178

Farmall 460 Running Rough...Any ideas?

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Hi all, great forum!

I'm having problems troubleshooting my 1961 Farmall 460 that suddenly started running rough while I was plowing. Sounds like it’s missing, both at idle and under load. There’s also a bit of black sooty smoke coming from the exhaust.

I started first with a thorough carb cleaning and rebuild; that didn’t help. It sounded to me like maybe water in the fuel or bad gas, so I drained and cleaned the tank, cleaned out the strainer bowl and fuel lines, and cleaned the carb again. Still no difference. At this point, I replaced rotor/cap/wires/plugs/condenser/points. When I removed the plugs, all 6 were covered in dry soot. Still no better. Pulled the new plugs to check compression, all cylinders were even (the exact value escapes me at the moment) When I pulled the new plugs to check compression, they were all covered in soot again (had maybe 10 min of run time on them). Running out of ideas, I tried another carb. Still doing the same thing. Finally, I replaced the manifold gaskets and I’m still having the same problem. The tractor starts up quick but within about 30 seconds starts loping and missing.

Any ideas? I’m thinking either a bad coil or a cracked intake manifold, or worse case a valve job/head gasket. I just would like some advice before I throw more parts at it.

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If the carb was rebuilt and adjusted correctly then you have to look at things like timing.

Try dumping a can of Sea Foam in the tank.

It still seems to me that there is a carb related issue tho like the choke is stuck or closing? Is the linkage OK?

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Thinking about this. It sounds an awful lot like something that happened to me a long while back.

I had my M on the blower and it sputtered and smoked until it got hot and then it actually did OK at full throttle and working hard.

Then I figured out that my new fuel delivery guy put diesel in the gas tank!

Must have been a 50/50 mix.

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Thinking about this. It sounds an awful lot like something that happened to me a long while back.

I had my M on the blower and it sputtered and smoked until it got hot and then it actually did OK at full throttle and working hard.

Then I figured out that my new fuel delivery guy put diesel in the gas tank!

Must have been a 50/50 mix.

That would do it.... Definately not diesel though. Since I first suspected water in fuel, I drained the tank and put fresh gas in. After it kept doing it, I took the tank off totally and cleaned it out. Then went and got fresh premium and put that in. No change. It seems to get a bit worse as it gets hot.

If the carb was rebuilt and adjusted correctly then you have to look at things like timing.

Try dumping a can of Sea Foam in the tank.

It still seems to me that there is a carb related issue tho like the choke is stuck or closing? Is the linkage OK?

Choke is OK. Linkage was disconnected for troubleshooting but I verified the choke butterfly operation. I swore up and down that it was a carb issue at first but after rebuilding the original carb then buying a replacement carb (and subsequently re-building that one just in case) I can't think of what else would be wrong on the carb side. It would be quite a coincidence if 2 carbs were bad at the same time, especially after 3 rebuilds.

Also, I checked the timing with a light. Looks like its very close to factory spec (according to the manual)

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Well that doesnt leave you much, does it?

Bad spark? Are the points malfunctioning? Bad condenser?

Only other thing I can think of are the valves or a blown head gasket?

Hows the oil and coolant? Anything unusual?

Cracked head?

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How about a cracked intake manifold or possibly a bad gasket?

If its sucking extra air it might do that.

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Try pulling plug wires one at a time to see if you can isolate the problem to a cylinder.

Only thing I can think of is a burned valve. Burned valves run good for a short amount of time until they warm up then they start running bad. Had it happen on a Cub Cadet. Did the ignition and carb 12 times, took a compression reading. The thing would fire right up and run like a top for about 90 seconds, then quit like you turned off the switch no matter what. With a 460, you've got 5 other cylinders to keep the engine turning, so it stays running.

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Well that doesnt leave you much, does it?

Bad spark? Are the points malfunctioning? Bad condenser?

Only other thing I can think of are the valves or a blown head gasket?

Hows the oil and coolant? Anything unusual?

Cracked head?

How about a cracked intake manifold or possibly a bad gasket?

If its sucking extra air it might do that.

I changed the manifold gaskets but that didn't fix it. A cracked intake is definately on my list of suspects here. Were there any known problems with the manifolds on the 460s? It looks original. I'll check for oil in coolant and vice-versa tonight when I get home. I wasn't initially thinking head gasket because of the even compression between all cylinders but I guess anything is possible. The condenser is new (that doesn't mean that it's good these days, unfortunately) and so are the points. Spark looks good, is there a good way to check spark quality? What about a weak coil?

Try pulling plug wires one at a time to see if you can isolate the problem to a cylinder.

Only thing I can think of is a burned valve. Burned valves run good for a short amount of time until they warm up then they start running bad. Had it happen on a Cub Cadet. Did the ignition and carb 12 times, took a compression reading. The thing would fire right up and run like a top for about 90 seconds, then quit like you turned off the switch no matter what. With a 460, you've got 5 other cylinders to keep the engine turning, so it stays running.

Would that cause all of the plugs to foul evenly though? It seems to me that if it was one bad cylinder the rest of the plugs would look good. I'm relatively new to old tractor engines though. I've almost resigned myself to an engine teardown at this point, I just want to make sure I don't miss anything obvious.

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That might be the case if it was only happening on 1 cyl but all 4? Kinda doubt it.

Unless maybe the rocker arm assembly is loose and the valves are not opening properly? Long shot I think.

Id look for a problem with the manifold first.

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How's the governor? Is it hunting to keep it running? If you are not sure try running it with your hand on the rod between the governor and carb.

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How's the governor? Is it hunting to keep it running? If you are not sure try running it with your hand on the rod between the governor and carb.

The governor looks ok, the rpms stay pretty consistent and I don't see any excess movement on the governor arm. I also ran it with the air cleaner disconnected from the carb to rule out a clogged pipe, it still ran the same way. The one thing that I noticed was that there was liquid fuel seeping into the air intake opening of the carb. I checked and adjusted the bowl but it still seems to be doing it. Was this typical for these downdraft carbs?

Otherwise, unless anyone else can think of anything, I'm going to blast the intake manifold and look for cracks. Thank you very much for the advice so far.

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Would that cause all of the plugs to foul evenly though?

What plugs are you using? Autolite 386 is the correct one.

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I had similar with a bad coil, but on a Case. Out of curiosity, when it's smoking and you turn in the fuel mixture screw, will it lean out and run smoother?

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How's the governor? Is it hunting to keep it running? If you are not sure try running it with your hand on the rod between the governor and carb.

The governor looks ok, the rpms stay pretty consistent and I don't see any excess movement on the governor arm. I also ran it with the air cleaner disconnected from the carb to rule out a clogged pipe, it still ran the same way. The one thing that I noticed was that there was liquid fuel seeping into the air intake opening of the carb. I checked and adjusted the bowl but it still seems to be doing it. Was this typical for these downdraft carbs?

Otherwise, unless anyone else can think of anything, I'm going to blast the intake manifold and look for cracks. Thank you very much for the advice so far.

Is this while its running or after you shut it off?

Ive seen gas come out the intake but only after shutting it off.

If its doing this while its running it sounds like gas is pouring into the system uncontrolled.

Maybe that carb rebuild job failed in some way? Something came loose like the float seat?

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Swap out the coil.

Those heat up over time when running and can short out, giving you less than the voltage needed.

Borrow a known good one and give it a try first to see if this fixes it.

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