8n Shuts off

mlbrantley

New User
I recently purchased a 1951 8n, the second one that I have owned. It set in storage for a couple of years. Good tractor for refurbishment or restoration. While it was trying to run it had trash in the fuel system. I replaced the tank, sediment bowl and the carb. Starts and runs great... for a while. After about 20 minutes or so, it starts skipping and then shuts off. If I let it cool down completely, I can restart and it runs about the same 20 minutes or so, shuts off again. If I only let it cool partially, it will start but only run a portion of the 20 minutes. Sound like it is heat driven.

I saw a similar problem on the forum a few weeks ago but can't locate it now. Can anyone help. Thanks in advance.
 
It could be the coil, condenser, ignition switch, vacuum lock as well as a few other things.

Rather than guess, troubleshoot the problem.

See tip # 13.

Post back w/ what you find.
75 Tips
 

with no vent in the tank and a non-vented cap, u can create enough vacuum in the tank as u use gas that the fuel will no longer flow. the easy way to test is to just loosen the cap and see how things go.
 
(quoted from post at 16:50:07 08/02/17)
If this is the problem, and I'm trying to verify, do I just need a new vented cap?

yes, or u can take your existing cap off and drill a small hole in it.
 

I failed to mention in my original request that this is a 12v conversion. I am focused on the Coil now, and if I replace it, do I need a 6v or 12v?
 
" I am focused on the Coil now,"

Why? Have you eliminated the more likely causes of your problem?

Are you using a 12 volt coil or a 6v coil w/ a resistor? (see tip # 30) Because if you have a 12 volt conversion and a 6 volt coil w/o a resistor, chances are very good that is your problem; the coil is burned up. So check and see if it's a 6v or 12v coil.

As soon as it stops running, do you have battery voltage across the points when they are open? (with the points open, put one probe on one side of the points & the other probe on the opposite side of the points) Verify the gap on the points at .025. Then, dress the points by running a piece of card stock or brown paper bag through them. New points sometimes have an anti-corrosive dielectric coating on them & old points can corrode or pick up grease from a dirty feeler gauge or excessive cam lubricant. (I always spray my feeler gauge blade off w/ contact cleaner.) Make sure you have voltage across the points, as in past the insulator on the side of the distributor. That is a very common failure point on sidemounts, along w/ the attached copper strip. It's hard to find a short there because it is usually an intermittent . So 'wiggle' the insulator & the copper strip a bit when you are doing your checking. If you find the short there, the Master Parts catalog lists everything you need on page 154. You can make the strip and you could also make the insulators as well. But, somethings are just easier & in the long run cheaper to buy. Get the strip, 12209, screw 350032-S, 12233 bushing & 12234 insulator & just replace it all.


If you just replaced the rotor & lost spark, put the old one back in. Insure that the rotor fits firmly on the shaft & that the little clip is there. Make sure the distributor cap is not cracked, doesn?t have gouges in it from the rotor or brass shavings & doesn't have carbon tracks. Check continuity on the secondary coil wire. Make sure it is firmly seated in both the cap & the coil. In fact, replace it temporarily w/ a plug wire. Next, remove the secondary coil wire from the center of the distributor cap, turn the key on & crank the engine while holding the end of the wire 1/4" from a rust & paint free spot on the engine. You should see & hear a nice blue/white spark. If not, you have a bad coil or condenser. Just put the old condenser back in to eliminate that as a possibility.
75 Tips
 

Bruce, thank you so much for the insight. Should I assume the swith on when checking for volts across the open points? Since the problem started I replaced the condenser, points and primary copper strip. Hasn't fired at all since. Still trying to remove the coil.

Thanks again.
 
(quoted from post at 11:20:37 08/04/17)
Should I assume the swith on when checking for volts across the open points?

yes. with the switch off, u should have no voltage at the coil and distributor.
 

Yes, you need the key on to check battery voltage to the points.

You might want to do that before you pull the coil off.

Is it a 6v coil or 12v coil?
 
(reply to post at 11:47:51 08/04/17)

Bruce, if I understand your instructions correctly, crank the engine until the points are open .025 (the normal setting), turn the switch the ignition on, check for voltage between the two sides of the points. If this is correct, there is no voltage. However, I do have continuity from the coil to the points connection. Sound like a coil or switch problem. You agree? I am now removeing the coil.
 
" You agree? "

NO!

Just follow the battery voltage and you will find the problem.

You have not confirmed a bad coil.

With the key on and battery voltage TO the coil, follow the voltage and see where it stops.

Post back.
75 Tips
 

I'm probably going to change the coil while I'm in therek. The old coil has no markings. Should I go ahead with a 12v? Is a balance resister required or eliminated?
 
(quoted from post at 17:15:45 08/05/17)
I'm probably going to change the coil while I'm in therek. The old coil has no markings. Should I go ahead with a 12v? Is a balance resister required or eliminated?

if you're determined to replace the coil, regardless of whether it's the problem or not, then get a 12 volt coil. the additional ceramic blob ballast resistor's purpose is to protect 6 volt coils from 12 volt batteries. a 12 v coil doesn't need that extra help.
 
I'd say there are 2 chances you have a bad coil: slim to none.

But, if you want to replace it, get a NAPA 12v coil, IC14SB. No resistor needed.

You can measure the internal resistance of your current coil to see if it's 6v or 12v; if it's 3 ohms or more, it's a 12v coil.

I'd suggest that you find the source of the no spark problem before you add more complexity to the problem by replacing the coil.
75 Tips
 

Bruce, thanks for being patient with me.

I have 12.5 volts at the + side of the coil with the switch on. Nothing out. When I removed the coil, it has no markings other than 11-95 on the bottom. Its beat up and old. The primary circuit OMs and the secondary (Distributor) are very close to the same OMs. My understanding is that indicates a bad or weak coil. Secondary should be much higher. That coil also gets to hot to hold if you leave the switch on for a couple of minutes.

I have a good coil out of an old corvette. 12 v External Resistor Required. The switch is the old 'pull push' with a fuse in it. Still works.

What would you suggest I try next? I owe you big time!
 

Congrats. Sounds like you beat the odds and do have a bad coil. Check the internal resistance of the Vette coil. If it's 3 ohms or more, hook it up and use it. If it's less, hook it up & get the tractor started. It will run fine w/ a low ohm coil for a long time until you can replace it w/ the NAPA coil.
 

it took about 125 - 150 hours for me to burn up my 6 volt coil with 12 volts without an additional ballast resistor.
 

oh duh, lol - u already have ;)

it'll just keep shutting down once it heats up till u get a new coil. it's not likely to do anything more drastic.
 

LOL, third time's the charm. your vette coil will take a good long while to burn up without the extra resistor. love that edit button :D
 

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