Tractor Engine Quits After A Couple of Hours

[Rubintropfen]

I have some experience with a few older tractors. The problem could be due to several things. I suggest you take a spark plug wrench with you the next time you run the tractor and when it dies immediately pull a plug, ground it to the block, and check for spark while trying to restart. If you are not getting a strong, bright spark then concentrate on the ignition system first. Another silly thing to try is running the tractor in the dark and looking at the spark plug wires for "stray" sparks. Replace all the spark plug wires if you got that issue (don't forget the coil to distributor wire, too). Make sure you set the timing correctly after monkeying with the points/condensor.

Another source of fuel system problems that you didn't discuss is the tank itself, and the screen in the tank. Rust in the tank could be clogging the screen, or even getting into the fuel line. You might just be able to drain the tank, remove the screen, and clean it, but if it is all rusted up you might need to seal the tank. I think the tank should either have vents, or a vented cap (not sure which on an MF35). If the vents are plugged then open 'em.

There is always the possibility of a "strange" problem, too. I once had a distributor with a centrifugal spark advance that was frozen; this caused severe overheating at high RPMs. A loose or cracked manifold can cause strange problems, especially if the intake and exhaust are leaking through to each other (some older tractors have a one-piece intake/exhaut manifold).

 

[rlk]

Thanks to everyone for your replies.

The latest is this:

Before running it Friday, I installed a clear plastic filter on the gas line. I wanted to be able to see if fuel was flowing to the carburetor when it cut off.

Ran the tractor for 3+ hours Friday. Had the gas cap just resting on the tank, not tight at all. After about 2.5 hours, it sputtered a few times, but did not cut off. After another half hour, it sputtered and did cut off. Since the gas cap was just sitting on the tank, there was no pressure or vacuum.

When it cut off, there was barely any fuel in the filter at all. Prior to this, the filter had been about half full.

This tells me that there is something in the gas tank that is blocking the flow. It only seems to do it after several hours of running, so I'm guessing when the fuel gets low, something in the tank blocks the connection to the gas line.

Usually I pour 5 gallons of gas in prior to running the tractor. 5 gallons brings it to about half full. I might try filling the tank all the way up to see if runs longer before cutting off. If it does, that definitely tells me something is in the tank blocking the flow of fuel when the fuel level gets low.

Following this test, guess I'll have to pull the tank to clean it and get it lined. I hate to do this, because the bolts holding the tank are not that easy to get to, plus you have to take the hood off, take the sediment bowl off, drain the tank, etc. As slow as I am, this will probably take a whole day.

Anyway, thanks to all of you, I'm slowly making progress determining what the problem is.

 

[Rubintropfen]

Take this with a grain of salt. None of it means you're not right.

I've heard that the clear plastic fuel filters might require more pressure than is present in a gravity feed system. Once the fuel in the tank gets low the pressure drops even further. It also bugs me that the amount of air in the fuel line would increase after the sediment bowl filled with gas (a good carburetor shouldn't leak air back into the fuel line, although maybe bets are off once it is starving for gas).

Could you try disconnecting the fuel line at the sediment bowl when it stalls out and prove that the fuel flow is restricted before that point?

You can probably check the screen in the bottom of the tank without removing the tank. Try draining the tank and removing the screen (and valve?) assembly. It works on an old Ford, but could be different on your MF. If the screen isn't really gunked up then I wouldn't worry about the tank. I would definitely try this before taking off the hood and removing the tank.

 

[Hydraman]

I had a clear plastic filter in my '79 low rider for years- strictly gravity feed- no problems. Also had them in garden tractors- gravity feed- no problems.

 

[djradz]

Before you pull the tank try this. Run it until it quits, then pull the hose coming from the tank to the filter and see it you get much flow from the tank. It could be that there's a filter in the tank that gets cleaned when you add fuel or the tractor sits, but over the period of an hour or two of running, junk, sludge, etc, collects around it. We had a boat fuel tank that did this. We would take the tank, throw some nuts and washers in it to act as scrubbers, and then shake the tank vigorously and work the nuts/washers especially around on the sides and bottom. Then pour them out and rinse the tank a couple of times with clean fuel.

 

[Rubintropfen]

Apparently the MF35 had a fuel shutoff valve with two inlets, similar to the Ford N-series. Opening the valve part way would only draw from the upper inlet, leaving some gas for transport in case you ran out. Opening the valve all the way would allow the lower inlet to operate.

If your valve is not open all the way, or if the lower inlet was plugged, then this would explain why you run out of gas with fuel visible in the tank.

<A target="_blank" HREF=http://www.ytmag.com/ferg/messages/12863.html>MF35 Fuel Tank Discussion on YTMAG</A>

 

[rlk]

Thanks to all who keep giving me more ideas.

I drained the tank again, this time letting it drain through the sediment bowl and the new filter I installed. The sediment bowl collected quite a bit of rust particles, some about as large as the head on a medium size nail.

Next I removed the sediment bowl and flushed the tank with gasoline. Collected a few more rust particles. Kept doing this until I did not get any more rust.

Reassembled everything and ran it for about an hour without it stopping. Would have continued running it but it got dark. It is misting rain today (thank goodness), so won't be able to give it a good test until later this week.

I've got my fingers, toes, and legs crossed hoping this resolves the problem.

Again, many thanks to all who have given suggestions.

Bob