Ferguson TO-35 strains and stalls after an hour of work

I can get it to do just about anything for an hour, but after that the engine starts to strain, with it dropping RPMs for a few seconds, then coming back up to normal, then dropping again, in a cycle. The cycle gets longer and more strained until she drops enough RPMs and stalls out about 20 mins after you first notice the problem. If I let it sit a day I can go out and run it again the same tomorrow. Running the mowing deck on the PTO seems to be the biggest factor. Any ideas?

Is your gas cap vented? Try popping the gas cap off when you notice it start.

How about a little more info? 6V or 12v system?

My gut feel is there is something restricting the fuel flow because you only have the problem under heavy load. But lets not jump to a conclusion.

I always check the spark first. A soon as it starts acting up, stop pull the center wire out of the distributor cap, hold it near a good ground and try to start. You should se a FAT, BLUISH-WHITE SPARK, the color of lightning. If it"s non existent or spindly and blue, reddish or yellowish, there is a problem in the primary ignition circuit (points,coil ignition switch, etc). 12V electrical system conversions either require a 12v coil( 3.2 ohms primary resistance) or a resistor in series with the 6V (1.6 ohm) coil. If it has the requisite FAT AND BLUISH-WHITE, then look to the fuel system.

Open the plug at the bottom of the fuel bowl on the carb. You should have an immediate and CONTINUOUS gush of fuel. If it"s just dribbling or is intermitent, then something is restricting it. The tank vent could be clogged, the tank valve may be clogged, the fuel line restricted, the screen at the carb inlet elbow clogged or the float valve partially clogged or misadjusted.
Do these checks sytematically and you"ll find the root cause of your problem.

It's a 6v converted to a 12v. I don't think the gas cap is vented. I'll give your suggestions a try tomorrow and post the results. I appreciate the help.

If you have a VOM check the reistance of the coil primary. It should be ~3.2 ohms. If it"s ~1.6 ohms look for a resistor. If you can"t find one, that"s your problem

Ign coil getting over heated.
It"s how old? Or made where?

I have had a similar problem in two of my TO's. One had a lot of crud in the tank. On a full tank, there must have been enought preasure to push the gas. The sloshing of the gas while driving would sometimes keep the gas flowing. I took the tank off and found dirt,rust, hay chaff,even a lead fishing anchor, plus things that are unknown. The second one was I think was a combination of electrical and fuel. I flushed that tank after seeing the first one. That one also had a lot of crud in it. When you have a 60ish year old tractor, who knows what is in it.

Do you have an inline fuel filter? If so, replace it or remove it.

swap out the coil, but if it's spitting and spurtering and you pull the choke and it gets worse then it's the condensor.

I checked the center spark plug on the distributor cap. The arc is bluish-white but not really fat, it's fairly spindly. I'm fairly new to fixing my own tractor. Can anyone tell me what the resistor should look like if I'm dealing with a 6v coil? Or the inline fuel filter? Here's a shot of the left side of the engine in case it helps:



It ran for about an hour today before the problem started again. I popped the fuel cap but didn't notice a difference. Here's a pic of it:



I also started unscrewing the bottom of this bowl (circled in red where I was unscrewing):



But it started gushing all over my hand so I tightened it back up. It's all clear and smells of fuel, I don't think there's any water in the bowl.

The resistor is needed if you have a 12V electrical system and a 6V (~1.6 ohm coil primary resistance) coil, It should be on the wire that goes to the coil from the solenoid or the key switch.

Before you remove the sediment bowl, you need to turn off the tank valve.

I have a 1957 TO-35 with 12 electrical system.
I have attached pictures of my fuel tank cap, note it has a vent hole in the top, original cap.

also i replaced my coil, with a bit hotter coil, made the tractor start and run better.

also installed a metal inline fuel filter, between fuel cutoff and carb, that has been a big improvement in good clean fuel to carb. There is bad stuff living and growing in those oll fuel tanks.

also, only use non ethonal fuel and autolite 386 plugs, i never had much luck with champion plugs.

Next time it does it, open the drain at the bottom of the carb and see if gas comes out quickly, like a man peeing after two beers. If it dribbles, like prostate trouble, remove the inline filter and try again. Even if new, it might be the problem.

Thanks for the helpful info guys, I'm going to pick up a new ignition coil, fuel filter, spark plugs and oil filter and try to swap those out this weekend, the last guy who owned the tractor didn't take good care of it and it likely needs all of these.

Also going to pick up the service manual but it's a little steep ($85). Anyone know what size fuel filter I need for a gasoline engine? (1/4", 3/8" or 5/16")

Probably you want to do all the work at once, but it would be really interesting if you could make one change at a time and check it.

Was finally able to get out and run the tractor for awhile (been raining). Swapped out the starter coil and spark plugs and she seems to be running better. Ran it for about 1.5 hours with no problems. I'll run it another couple hours today and see how it goes. Thanks for the help!