Ford 640 stops running

flyineagle

New User
New to the group & fairly new to tractors.... I have a 640 that has just started not wanting to run for very long. New battery, starter, selonoid, points, plugs, wires and fuel tank. Starts right up and runs nice for about 15-20 minutes while bush hogging then suddenly misses, spits & sputters. If I push in the clutch it will idle fine until I release the clutch and when it gets a bit of a load from the brush cutter it again sputters and wants to shut down. After a few minutes it stops. Let it sit for a few minutes it starts right up - start cutting and after less than 5 minutes same thing. I was able to get it to the carport and it kept running great until I tried engaging the cutter and release the clutch with it in 1st gear. I ran it 2 days ago for about 3 hours and not even a hiccup. And there is about 4 inches of fresh fuel in the tank. Thoughts, suggestions, solutions greatly appreciated. Jeff
 
Does it have the heat shield between the gas tank and the manifold?? If it doesn't the gas could be boiling. Carefully take the gas cap off when it does that. If you see the gas is boiling you found the problem. Or if when you take the cap off you hear a suction sort of sound the tank vent it clogged. Next check to see if the coil is so hot that when you spit on it the the spit steams of the coil maybe going bad
 
Not to beat a dead horse, but what plugs did you use? I have had just such an experience w/new plugs made in the "land of almost right", & that includes many of the plug names that used to be considered the best. They sound really good until you work them a little, then miss & backfire & have almost no power!
 
Yes, the heat shield is in place. You mention the same as others that it could be the coil - I'll check that later today. Many thanks, Old!
 



Classic fuel blockage. A bad coil takes an hour to cool off. You need to test for FLOW of fuel, not presence. Remove the plug from the float chamber of the carb, catch the gas in a container. You need to get approx 16 ounces in two minutes. It could be the screen inside the tank or the screen at the top of the glass bowl. Sometimes there is an additional small screen at the carb inlet.
 
I had similar issues with my NAA years ago. It acted like it was starving for fuel. Went through the whole fuel system no help. It turned out to be the coil and it didn't have to sit for an hour to cool down, only 10 or 15 minutes and it would fire right up and run for another 10 minutes and then start missing and surging.
 
Down to 2 things, fuel supply and coil. Test fuel flow to carburetor good chance there can be crud blocking the valve at the tank. Have to actually check and watch flow volume.
Check primary resistance of coil and then if it dies have a spark tester and check for spark immediately
My money is on fuel supply.
 
(quoted from post at 07:30:04 05/11/22)


Classic fuel blockage. A bad coil takes an hour to cool off. ...

Not all coils fail in exactly the same way. Many will take some time to cool off to where they will allow the engine to run again, while others can allow the engine to run sooner. In most cases, the amount of time it takes to get to the point where the engine shuts off gets shorter and shorter as the coil gets worse and worse, and the time to cool off and allow the engine to run gets longer and longer. Also, it depends on the ambient temperature as to how fast it will cool overall, so if the tractor is in a location where the weather is still fairly cool it will cool off faster.
 
Sean, what was that stuff you suggested to another poster awhile back to spray on the coil as soon as it started acting up?
 
I have a Ferguson TO-30. I know, not your tractor.

However, I had a similar thing. Driving level and downhill no problem. Going back up hill under load missed and sputtered but kept running. What gives? Checked everything else except what I should have done first, except I didn't believe that it could possibly be a "Failing" condenser. Replaced and all was good. I alway thought a condenser was either good or bad, but never sad. Cheap fix if that's it.
 
A can of electronic duster would do the trick. It cool things down very fast and you sure don't want to spray it on your skin because it will freeze the skin
 
(quoted from post at 12:05:56 05/12/22) Sean, what was that stuff you suggested to another poster awhile back to spray on the coil as soon as it started acting up?

They used to make "freeze spray" for electronic troubleshooting back in the day when there were more discreet components that might only have problems once they warmed up. The can came with a straw similar to the ones that come with the cans of spray penetrating oil, so that you could spray it on individual transistors, capacitors, coils etc. to cool them off one-at-a-time to se which one might get things working again once it cooled off. Everything has been so consolidated into multi-function chips and circuit boards that are meant to be tossed and replaced, that I haven't used it in my electronic troubleshooting for many years, but I still have a few cans around from back in the day when I used that stuff at least several times a week in my job.

I just did a Google search on "freeze spray" and there are several still on the market.

Any aerosol can will provide at least some amount of cooling when it is sprayed directly on something, even the "electronic duster" that old mentioned, but that is really just compressed air so it would provide the least amount of cooling of any of them. Something that sprays a volatile liquid that then evaporates away quickly provides the most cooling power as it combines the cooling power of the compressed gas expanding when sprayed with the cooling effect from the liquid evaporating.
 
You haven't posted what you discovered after checking the coil.
NAA shop service Manual states 1.05-1.15 Ohms for Primary, and 4.00 Ohms for secondary both at 75F.

Rereading your post I see you replaced points, and presume you did the condenser too.

Only one thing left is Carb. Very simple after you get it off to check for debris. You "may" need a new gasket afterwards.

Let us know what you discover.
 

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