tractor quits running

[jack nance]

I have a tractor that quits running after about 30 minutes-when I change spark plugs it runs again for about 30 minutes-my plugs are very oily when I replace them.
Do I need a new set of rings?
Thanks,

 

[old]

Well with out more info all I can say is maybe the problem is the nut behind the steering wheel. Just joking but we need a good bit more info to be able to help you much. #0 minutes can be many things on many tractors so it is hard to do much. I can say the moment it stops you need to check for spark and then you need to check for fuel. As for oily plugs that 2 could be a number of problems any thing from bad rings bad valve seals to sticking rings to the wrong oil in the engine

 

[730d se]

What make, model, and year is it?
Also on the list could be a partially blocked air intake or an over filled air cleaner oil bowl.
Is there smoke out of the exhaust and if so, how much and what color? If smoking, is it just at throttle advance and under load or all the time?

 

[bill b va]

try a set of the hottest plugs you can get . the new formulated gas of today may be the problem . forget about what the spects call for as they were written before the epa got involved .

 

[Brad_bb]

Well, I can say I've had a similar problem. A couple things, are the plugs oily or sooty? I'm betting sooty, which would indicate an overly rich mixture or flooding condition. This would indicate that it's a fuel related problem, but you will need to clean those plugs before reinstalling them. A simple small wire brush will do, a shot in a glass bead blasting cabinet will work too, but wire brush is sufficient. What I've found is that my carb needle tends to stick, especially when it hasn't been run in a couple weeks or more. I ask why does it stick? In my case, I do not believe it to be dirt or debris. My tank is clean, and my sediment filter is clean, and I've never found evidence of debris in the many times I've taken it apart. My speculation is that the viton tip of the needle is swelling from ethanol in the fuel. This seems to always occur the first running of the season after it's sat for the winter with Stabil in the fuel(my tractor is stored in a heated building). Inevitably the needle sticks and gives me problems until I've actuated the needle a number of times and run it a bit. Back to the problem, a sticking needle(open) will cause flooding, because it will allow fuel to over flow the bowl and migrate into the intake side of the carburetor. In some cases, when the fuel valve is left open, fuel can continue to migrate and fill the intake tube, fill into the intake manifold and into any open cylinder who's intake valve is open. This extreme case will make starting very difficult and will force fuel past the rings and into the crank case and mixing with the oil.
On the other hand, when the needle sticks closed, this will choke off your fuel supply and cause your tractor to die. I have had both situations on my tractor. I've replaced my fuel tank valve and I have tested it to know it works properly now, so next winter I'm considering draining the fuel from the carb bowl so that my needle will sit without fuel in the air(float down).
As I said, the solution is usually actuation of the needle, both lightly by hand, and running of the tractor(which opens and closes it regularly).
Lastly, your plugs, which I'm assuming are sooty, is caused by an overly rich mixture either from flooding, or the setting of the carb. I'm assuming yours is like my Marvel Schrebler which has a mixture adjustment for under load condition, as well as and idle adjust. Additional information could lead this in another direction.
Oh, another possible cause is a vacuum leak. Years ago I had a vacuum leak create the same conditions as you are describing also. My intake manifold was loose, enough so that when it heated up(20-30 minutes of use) expansion would cause a small gap to open up at the intake gasket, leaning out the mixture and killing the tractor. Check your manifold nuts/bolts to make sure it's not as simple as that like mine was. Another way to identify a manifold leak is to spray carb cleaner around the intake gasket area and if engine RPM increases, you have a vacuum leak(carb cleaner sucked into the engine at that point). Use caution though as you are near the exhaust manifold. Hope this helps get you in the right direction.

 

[CNKS]

Bad coil, changing the plugs gives it time to cool off. If it is the plugs, it will sputter and miss before dying. If the coil, it may sputter a little, but dies after a very short period of time.

 

[36 Coupe]

Put a steel needle in the float valve.I found the viton tip sticking often.A carb rebuilder wont use viton tips in his rebuilds.