1950 8n stalls, restart fails

My 1950 8n stalls after 5-15 minutes. The stall has happened 6 times and always under load while using a 5 foot rotary cutter in 2-3 foot grass (the cutting and tractor move effortlessly). Restart is never immediate and fails from anywhere between 4 hours and 4 days. Prior to any stalling of this nature, I replaced the fuel tank, sediment bowl, fuel lines, and replaced the carburetor with a new one when the rebuild carb did not work out. The fuel system was replaced because it was the original and full of rust causing the fuel flow to be a trickle and only allowing the tractor to use fuel immediately in the carb before stalling. The fuel system replacement was a great fix for 2 weeks when not under load and driving the tractor for approximately 16 miles at different speeds in all gears. Stalling after the fuel system replacement was always under load and could possibly happen when not under load, but I did not have the opportunity to discover whether that can happen when not under load.


Initially, I thought the coil was getting hot, so I replaced the coil and the tractor would not start. I had a new set of plugs, wires, condenser, rotor, points, and cap that I changed to (the previous rotor, points, and condenser were new two months prior) and still the tractor would not start. The ignition switch is two months old and seems to work as it does complete the circuit and I can see spark. The fuel system is fine with a steady flow to the carb. Voltage is fine, getting spark to the coil and distributor with gap set at .025 as usual on 216 plugs and points. The tractor was down for 2 days before I was able to start it and get it on trailer. I’m thinking replacement of the wire harness, but why spend money that doesn’t need spending if the fix could be lesser… Anyone have ideas to the issue of stalling under load and failure of a restart that appears random when it will start? The tractor is 6 volt with the side distributor.

Before you throw more money at it determine if it is
a fuel or spark problem. As soon as it dies, get off
the tractor and check the spark (use an old plug gaped to 1/4" and grounded to the block someplace)
If the spark is good (blue-white and snappy), then
check for fuel flow (remove drain from bottom of
carb bowl. Catch in a clean container - should be
about a pint in 1-2 min.

" I’m thinking replacement of the wire harness, but why spend money that doesn’t need spending if the fix could be lesser…"

Why not? You've replaced just about everything else & have yet to figure out if you have a spark or fuel problem.

That is the very first thing you need to do before you start buying parts.

It takes three things for an engine to run: spark at the right time, compression, & fuel in the right mixture. For the moment, forget about compression & concentrate on narrowing the problem down to spark or fuel.

There are three very important tools you always need to have in your N tool box: a 3 inch piece of wire w/ alligator clips on each end, an old spark plug w/ the gap opened to at least 3/16” ( ¼” is better) and a 7/16 box end wrench. (see tip # 50 at the link below) And, you really do need a working ammeter on the tractor; it is a very important diagnostic tool. With these tools, you can quickly narrow down most N problems to spark or fuel.

As Harold said, next time it stops, check quickly for fuel then spark. When we say quickly, we mean get off the seat, grab the tools & do it right then. Do not wait a minute or two. First, check for fuel. Get a can & put it under the carb. Remove the bolt in the bottom of the carb; as long as the fuel is turned on, you should see gas flowing out of the carb. Let it run for at least 30 seconds. If it’s a dribble, or runs for 5 seconds & stops, or none at all, you have solved half the problem: it’s fuel related. If gas flows well out of the carb & only stops when you turn it off at the sediment bowl, chances are very good it’s not a fuel problem. So, next, turn the key on, crank the engine & look at the ammeter. What is the needle doing? Does it show a constant discharge, no movement at all, or does it move back & forth slightly? Next, get the old plug, ground it to a rust & paint free spot on the engine, turn the key on & crank the engine. If the spark jumps the 3/16” gap, you probably don’t have a spark problem. If it won’t jump the 3/16” gap, you have a spark problem. If the ammeter needle shows a constant discharge, or doesn’t move at all, that also tells you that you have a spark problem. Jump the ignition switch w/ your jumper wire & see what happens. If it runs, you found the problem. If it doesn’t have spark after you jump the ignition switch, post back for more info on further troubleshooting. (and do not forget to turn the ignition switch off; see tip # 38)

If it does not have gas coming out of the carb at a steady stream w/ the bolt out for at least 30 seconds, you have a fuel problem. First, remove the gas cap. Your vent could be clogged & it vacuum locked. If that doesn’t work, tap the carb bowl w/ a hammer handle in case the float is sticking closed. (don’t whack it w/ the head of the hammer; you can crack the bowl). If you still don’t see gas flowing, the N has three fuel screens; one in the brass elbow, one in the top of the sediment bowl & one on the stem of the sediment bowl in the gas tank. Check the screen in the elbow & the screen in the top of the sediment bowl. (don’t worry about the one in the tank) Both probably need to be cleaned. If you have the fuel knob turned on all the way, & 1 gallon or less in the tank, it may be trying to feed off of the reserve inlet which is probably clogged. Only open it 2 full turns. Put at least 2 gallons in the tank. (and do not forget to turn the gas off; see tip # 9)

There are ways to check for spark & fuel that work & ways that don't. For example, having gas to the carb is nice, but having it past the float is what counts! " The fuel system is fine with a steady flow to the carb" You don't know that yet. That’s why removing the 7/16” bolt in the bottom of the carb is the way to check for fuel. And, same thing w/ spark at the plugs. Some folks think that checking for spark means pulling a plug wire off & looking for one. Well, it's the distance the spark jumps at the plug that gives you the info you want. It takes about 17kv to jump a 3/16" gap & 22kv to jump ¼” in the open air. Remember, it’s 14psi outside of the engine & about 90psi at a 6:1 compression ratio in the cylinders & compressed air creates electrical resistance, so you really need the 17-22kv to fire the plugs when the engine is running. A store bought plug checker will work better than an old plug because it won’t shock the snot out of you like an old plug might!
50 Tips

Farmwiser.......would you believe that yer M/S carb bowl has about 5-mins of gas for running.
Howsomevers, yer weaksister ignition switch will cut-out on you inna'bout 15-mins and STALL. It generally cools itself down innna'bout 30-mins and will restart. Do I haffta tell you to replace yer weaksister ignition switch??? ($10, cheap) .......Dell, yer self-appointed sparkie-meister