Fuel or spark?

July 23, 2020

Greetings,

My name is Don, I am a tractorholic and I need advice! (That used to be funny. Not so much, lately.)

I bought my 1948 Ford 8N (8N94754) in 1986. My mechanical & licensed electrician good friend, Rick, completed a very major overhaul 385 hours ago in 2012. Since then additional upgrades as noted below:

Problem:
Tractor starts strong and runs perfectly until it does not. After 45 minutes or so of constant pasture mowing work-load the engine begins to stutter and within two minutes it is running very rough, sometimes back-firing. However, it will idle just fine. After allowing a cooling period she is ready to go back to work, but 45 minutes later the problem repeats. It behaves much like a car of mine years ago which had a vapor-lock issue.

Having followed this forum for years I know when a member describes rough-running issues the advice usually concerns fuel or spark. And this may still be the culprit but let me list our repair attempts:

Pertronix electronic ignition, new remote coil, NGK #B-6L plugs, no ballast resister.

New fuel line installed and insulated hoping to cure imagined vapor-lock.

Rebuilt carburetor

Fuel bowl & carb filters perfectly clean - passed 2-minute gas flow test.

Drilled .067 hole in gas cap to relieve imagined gas tank vacuum issue.

Note: The new fuel line runs close to the (hot) vertical exhaust preventing a safe inspection of the carb filter and fuel flow in the field.

I will not be surprised when the fix is obvious to the more experienced on the forum. All suggestions are invited and sincerely appreciated!

Don
Sherwood, Oregon
[email protected]

I think you are right about vapor lock. Try putting on a new fan belt. My tractor used to run hot, nearly into the red part of the gauge until I tried the new fan belt. Now the needle barely moves.

I think 45 minutes is a long time for a fuel problem to show up. So I would look at ignition. The next time it starts acting up, have a jumper wire handy and use it to bypass the ignition switch, or just bypass the switch and go out and work the tractor. Then if that doesn't help, feel the remote coil and see it it's hot to the touch. 45 minutes is a long time for a coil to brake down too. If you could check for a good strong spark with an adjustable spark tester set at 1/4 inch or an old spark plug with a 1/4 inch gap would be ideal. If it isn't the switch or coil, then I would suspect the Petronix.

Cheap easy test, wrap aluminum foil around fuel line and filter. Does not have to be pretty for a test.
If it does not work you are not out much.

No fuel pump, so it won't vapor lock. But, if you have ethanol in the gas, or 'winter' gas in the summer, it could be boiling off. Put a pint or two of diesel
or kerosene in the tank.

Next......


You could have a spark issue.


You could have a fuel issue.


Don’t guess. Troubleshoot. See tip # 13 at the link below.


As soon as the tractor starts running poorly ( NOT 5 minutes later) you need to answer 2 questions before you do anything else:


With the bolt in the carb bowl removed and the gas on, will the fuel flow fill a pint jar in less than 2 minutes?


Next, get out your adjustable gap spark checker * , open the gap to 1/4", hook it up, turn the key on and crank the engine. Does the spark jump 1/4"? Post back
with the answers.


And do not buy a new part for the tractor until you can answer this question: how do I know the part on the tractor is defective?

Once you narrow the problem to spark or fuel, post back and tell us what you found (and how you found it) and you will get plenty of help to get your tractor
running.



* Don't own an adjustable gap spark checker? Buy one! Not a test light! Until then, take an old plug, open the gap 1/4" ground it to the head & look for spark.
It’s not the color of the spark that counts; it’s the distance it jumps.
75 Tips

I had not thought of a fan-belt problem. Thanks for the suggestion. Would not hurt having a spare on hand anyway.

All good suggestions. I just ordered an adjustable spark tester. Thanks for the help.

You and I think alike. My shade-tree insulation consisted of a layer of fiberglass and then a wrap of aluminum foil. All held on with wire-ties. I wrapped the entire length of the brand new fuel line.
Thank you.

Bruce, I am fairly sure there is ethanol in the gas. I will add some diesel as suggested.

To all of you very helpful guys, thanks for the replies. It will be several days before I get back to the Forum with news.

Incidentally, I buy all of my parts from Yesterday's Tractor Co, Port Townsend, WA. Great Customer Service and one of our favorite PNW towns ... a gateway to The San Juan Islands & Canadian BC.

Some times it takes awhile to get to the bottom of what is going on
these tractor can be frustrating, but I do know my Ferguson TO-30
runs 110 percent better when I use Non Ethanol gas its amazing how good it runs
it starts good and idles smooth.

(quoted from post at 14:56:21 07/24/20) Bruce, I am fairly sure there is ethanol in the gas. I will add some diesel as suggested.

To all of you very helpful guys, thanks for the replies. It will be several days before I get back to the Forum with news.

Incidentally, I buy all of my parts from Yesterday's Tractor Co, Port Townsend, WA. Great Customer Service and one of our favorite PNW towns ... a gateway to The San Juan Islands & Canadian BC.

Click to expand...

Oregon gas has 10 percent ethanol year round! You can buy non ethanol at a lot of stations, but it can get expensive. I would try the bypassing the ignition switch to start with or only mow for 30 minutes and take a break and sit in the shade! I have no problem with the ethanol gas in either of my 8n's by the way and I am not that far away from Sherwood!

July 30, 2020 Spark or Fuel UPDATE:

Yesterday, after mowing for 25 minutes the engine began a very steady, almost unnoticeable miss. But over the next 10 minutes the miss kept getting worse until it was very pronounced. The tractor was not happy at throttle at which I was mowing but (without load) was OK at throttle and also at complete idle.

Jim L WA - The coil was way too hot to touch. Based upon this touch test and the following web information I suspect internal coil damage caused by this extreme heat. Thanks, Jim.

Per the web:
Most ignition coils are long lasting and reliable, but a weak coil can be the cause of under-hood havoc. It is possible to have a sudden coil failure due to broken windings or bad connections inside the coil. However, it is more common for coil problems to show up as hard starting, A REPEATED HIGH-SPEED MISS OR A GRADUAL DECLINE IN IGNITION SYSTEM PERFORMANCE. These kinds of coil problems are usually caused by heat and vibration.

So, I have ordered a Pertronix Flame-Thrower 40,000 volt epoxy-filled coil and will be relocating it to a cooler location. FYI, Pertronix offers oil-fill and epoxy-fill coils. Epoxy-fill coils can be mounted horizontally and are recommended for tractors where heat and vibration play a part.

I also added 1 quart of diesel to the full gas tank, as suggested by a Bruce (VA). No difference whatsoever and that includes exhaust smoke there was none.

Adjustable Spark tester shows a strong, white, lightening-bolt that easily jumps " actually .300 measured. Thanks to Jim L WA and Bruce (VA) for this suggestion.

Fusion 1, if I need to start using non-ethanol gas I will do so and will let you know. Thanks for the suggestion.

R Geiger, your suggestion is the most appealing of all: . or only mow for 30 minutes and take a break and sit in the shade.


Thanks again for all of your help, fellas. I will give you another update after the new coil is installed.
Don Miner

if you immediately measured that spark before anything had a chance to cool off, it should not be your problem. 140F is about temp most can not keep hand on and it is not at all uncommon for coils to run about 200F. As the copper windings heat, resistance goes up and consequently current goes down. So, just normal operation results in a reduction of coil current , thus resulting in a about 60 to 70 percent spark energy when hot vs at room temp, but most well engines perform fine at that level.

August 20, 2020 - Spark or Fuel UPDATE:

Well, the Flame-Thrower coil is installed and from a cold start the length of the white, lightning-bolt spark is an impressive (measured) 0.500 at roughly 600 rpm. I also followed the Pertronix suggestion to increase the spark plug gap. Their recommendation: an additional 0.007 gap (0.032 total) will increase horsepower a bit. I am unable to confirm their increased horsepower claim but can report that after mowing for over one hour all systems are a GO and my 8N is again happy earning her keep.

There is a wealth of experience and talent on this Forum that is free for the asking!! Until next time, my sincere thank you to all who read my posts and offered helpful suggestions.

Don Miner
Sherwood, Oregon

Again, we should all take R Geigers suggestion or only mow for 30 minutes and take a break and sit in the shade.