MF50 runs rough under heavy load

c_shell351

New User
Hello everyone I'm new to the forum and have a question concerning my MF50. I'm not sure of the year but anyhow it has the 4 cyl gas engine. The problem I'm having has been ongoing for a year or so now. The tractor will start and idle just fine and it runs great until you get it hot and in a good pull like pulling a 6' disc or 6' bush hog in heavy grass. Then it wants to spit and sputter until you mash the clutch and it'll clear up a little but still won't run very good. I have to hold the choke just to get it back to the barn. Then you let it sit a little while and it cranks up and runs like there was never a problem until you get it in a pull again. I just rebuilt the carb in hopes to fix it to no avail. The fuel tank is clean on the inside. I've also thought it could be vapor locking but I have new 1/4" rubber hose from the new sediment bowl to the carb. The points look good and are gapped to .022" New plugs and wires. Any help will be appreciated. I'm about ready to make a trip to the scrap yard.
 
Sounds like the ignition coil is going bad, that's how they act when they get hot, but run fine cold up to about 1/2 hour. That's why I prefer diesels, but haven't got Tony convinced yet...
 
I definitely agree with the diesel being better! I also have a 135 diesel that's a sweet little tractor. But concerning the 50, You think its the coil even though pulling the choke makes it run? I was thinking it was fuel related because of that? I think my pop replaced the coil not too long ago but I'll make sure and change it if he didn't.
 
My least troublesome tractor is the one I took out all the fuel filters an added a ball valve with one inline filter
which is clear plastic so when its out of gas you know, only bad is no reserve.
 
How long does it run well without the choke? You may also need a new fuel cap, if the vent is plugged no gas out if no air can get in. See if it runs better when hot after loostening the fuel cap, if so cap is bad. If no change I would still suspect the coil if carb settings are correct.
 
C,
I feel your pain, I have an old TO-35 1957 model with the z134 gas engine,

when running good, they are a great little tractor, but when not running good, they are a pain in the butt.

I would start with a fresh tune up. I use autolite 3116 plugs, others over the years will cut out and not last as long.
I buy tune up parts at napa as parts from some of the box stores are less quality.

change the coil as others said, one time my tractor would start run until it warmed up then die, someone said, as the coil got hot and expanded, it had a broken wire inside, the wire would separate, causing the tractor to die. replace it with a hotter coil, if you can find one.

but, a classic sign of a carb stopped up: at normal operating temperature, it will run better when you pull the choke, it should not run better with the choke pulled.

my old tractor, I use the choke for a cold start, yes these old tractors were a bit cold collared, so I feather the choke some until it warms up a minute, but after that warm up period, I never use the choke. never have to use the choke if I restart it as I working in the orchard etc:

I placed a metal fuel filter between the carb and the fuel cut off valve, you can almost never get all the dirt out of these old tanks. your carb has a fuel filter in the elbow, take it off and clean if you have not done so. the fuel cut off valve has a filter screen in the top of the cut off above the glass bowel.

secure a good manual and know how to adjust the carb, tractor must take fuel when you apply a load, like dropping the disc or plows in the ground, then pulling down on the fuel lever.

I will look up a carb adjustment site for you, if I can still find it.

again, start with a fresh tune up, clean air filter stack, then on to the carb, are the wires radio resistor wires, if so they cut your power in half, should be copper core wires, only the best for the little fergy.
a187467.jpg
 
http://www.external_link.com/M_S_TSX_Carburetor.html

this site might help with carb information if you have a tsx carb.
my tractor has a ms-tsx605 carb, yours may have a larger one, but they will be adjusted and cleaned about the same.

you need to know what carb you have

good luck and keep us informed of your progress.

do not take the tractor to the junk yard just yet!!!!!!!!!!!!!!!!!!!!!!
 
thanks for the info! The plugs and wires are pretty new, and like I said I just rebuilt the carb and it seems to be adjusted pretty good. If its at idle, you can gag it wide open and it'll take the fuel just fine. it only runs bad when its been under a good load for a minute or 2
 
It may be electrical, but before you buy parts I would see how much fuel is getting to the float bowl. My MF-20 has a fuel shut off valve there. If you do on yours remove the valve and see of you get a constant stream for several minutes. Hope this helps. Gerard
 
also when doing the fuel flow try it with and with out the fuel cap on.
had trouble with my 202 with low fuel flow .
it would not drain out of the tank fast enough .
 

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