Open the fuel valve two full turns for normal operation, and all the way out to get the remaining one-gallon reserve at the bottom of the tank (along with whatever sludge and debris may have collected in the tank). Honestly, using the reserve is just asking for trouble. There is supposed to be a screen around that reserve fuel port in the tank, but no way to verify it is there, and in good condition, without removing the entire fuel valve assembly.
It is highly recommended that you always close the fuel valve completely when you shut the tractor off for the day. This is a gravity-feed system, and the tank is above the engine. If the float in the carb does not seal, all of that fuel could end up in your engine. Especially if it has a couple of days to drain.
The Ford 8N Tractor fuel system has three (3) screens. All three of those screens need to be clean for proper fuel flow. A good way to test the system is to put a can under the carb, remove the large plug at the bottom of the carb, and then open the fuel valve on the tank. You should get a good steady stream of fuel after the carb drains. If the flow of fuel slows down significantly after what is in the carb is gone, start looking for the problem.
As mentioned above, one screen is in the tank. You have to completly drain the fuel and remove the fuel shutoff valve assembly to clean that one. Don't forget to also drain the reserve fuel supply by screwing the fuel shutoff knob all the way out. If you don't, or that screen is badly clogged, you will still have about a gallon of fuel in the tank when you remove the fuel valve assembly. Ask me how I figured that out. Before starting this repair it might be a good idea to have a replacement fuel valve assembly. The old one can probably be cleaned, but a replacement will have your tractor ready to go again much faster. You can always rebuild the old one, and keep it as a spare.
A second screen is located just above the glass sediment bowl at the bottom of the fuel shutoff valve. Loosten the bottom nut, remove the glass jar, and the screen is above the seal. Before removing the glass bowl, it is a good idea to have a replacement gasket and filter to put in there. It might not be a bad idea to have a replacement glass bowl in case the old one gets dropped on your concrete floor.
The third screen is attached to the fuel inlet elbow on the carb. Remove the fuel line and unscrew the brass elbow to get to that one. It is made right on the end of the brass fuel line elbow adapter.
If any of the screens is clogged, look immediately upstream to find the source of the problem. Usually the problem will be a dirty or badly corroded tank. Flushing and cleaning the tank may help, but if the problem is corrosion, you need to fix it or get a new tank. There are several tank repair products available that coat and seal the inside of the tank and may fix the problem. Make sure the coating is suitable for ethanol fuel if you run pump gas with ethanol.
When replacing taper-threaded fittings don't forget to use sealant on the threads or they will leak. Don't use regular plumber's tape, use the sealant that is suitable for natural gas lines and fuel systems. It comes in a tape roll similar to regular plumber's tape, but it's usually yellow color and thicker than the teflon stuff. There are also brush-on products if you prefer.
The fuel line is a flare fitting, the threads on this type of fitting don't seal anything, so there is no need for sealant on the fuel line fittings. Just make sure both the pipe and the socket are clean.
Thoroughly clean and inspect fuel line, and fittings. Replace parts that are corroded, or if hex nuts are rounded-off.
Please, DO NOT use rubber hose, add inline fuel filters, or use anything but plain steel tubing for the fuel line! Rubber hose next to a hot manifold becomes an instant fire hazard. The in-line fuel filters are generally too restrictive for a gravity fuel system. They may flow ok with a full tank, but when there's only a gallon ot two left, there's a lot less weight pushing fuel through the screens. Adding anything other filters usually causes fuel flow issues.
I often see copper tubing substituted for steel. Obviously when replacing a rotten fuel line, a previous owner decided to more permanently fix it. There are several problems with copper tubing. The cheap, plain steel fuel line was used on purpose. The engineers knew that when dissimilar metals come in contact, and are exposed to weather, one will always become sacrificial, and protect the other. Their intent was to make the least expensive, and easiest to replace part, the sacrificial part. That is why the fuel line is plain steel. When you use copper your gas tank becomes sacrificial! When we replace a rusty fuel line, all that ugly rust is rust that didn't form on or in the gas tank! Copper tubing is also softer then steel. The soft copper will work harden, and crack at the fittings, which is of course a fire hazard. I mention fire because a little fuel leak, plus a few sparks, in the middle of a dry hay field, occasionally leaves a tractor owner with a few very fast decisions to make before he becomes the weekend barbecue.
Modern pump gas is getting less and less friendly to these tractors. The steel fuel tank located directly over a hot engine can easily get hot enough to literally boil the fuel! This has always been an issue with the design, but modern fuel formulas boil at lower temperatures. It used to be possible to run fresh gas through a carb that had gotten gummed up. The fresh gas would often dissolve gum, and clean it out. With modern fuel, any carb issue means I just swap carbs, and put the old one with the others to be cleaned.
UNLEADED GASOLINE: Even though this is an antique engine, it is not necessary to add lead to the gas or use hi-test gas. The Ford tractor engine is a low compression (6.5:1), low hp (25-30 hp) industrial engine with hardend valve seats for long life. It will be perfectly happy, and run best on regular low-test unleaded gas.
ETHANOL FUEL: I have not noticed as many problems with the current ethanol-blended pump gas. I believe the 10% ethanol fuel reduces engine power by approximately 5%. I have also noticed a different type of gum buildup inside my carbs, that eventually clogs them up. These observations are opinion, and not proven facts. Perhaps I should apply for a government grant to do a comprehensive study?
BOILING FUEL: There is another issue with these gravity-feed fuel systems. The enclosed fuel tank location directly over the engine can soak up a lot of heat on a hot summer day in the fields. Modern pump gasoline with 10% ethanol has a lower boiling point than straight gasoline these tractors were designed to use. There have been cases where the fuel was boiling in the tank! That is not a comforting thought! Besides being extremely dangerous, boiling fuel creates bubbles in the carb, disrupts metering, and the engine simply cannot run right with bubbles in the system. This could become a more common problem for these tractors. As the ethanol percent blend increases, the fuel boiling point gets lower. Fuel injected vehicles are immune to this problem because the tank is remote, and the fuel is under pressure all the way to the cylinders. A simple solution would be to relocate the tank away from the engine. But there really is no good place for it to be, and we would have to add a fuel pump for it to work. With the tank under the hood, we could add spray-on insulation, or a steel double-wall air gap to the bottom of the tank. Of course there isn't a lot of room to add anything between the original tank and spark plugs. There are some approx. 5 gallon surplus and replacement tanks that were designed for portable generators. They are the right shape, size, and the only real challenge is finding one with the fuel cap in the right place. With a smaller tank there would be more room to add a metal baffle / air gap below the tank. Some fuel tanks are a molded plastic material that would solve the rust problem and be a better insulator than steel. For my purpose, having a smaller tank would not be a huge disadvantage.
DRAINING THE FUEL: If you let your tractor sit, unused over the winter months, this is considered short-term storage. You should put some Sta-Bil or equivalent fuel conditioner in the fuel to keep it fresh. It is also a good idea to keep the tank nearly full of fuel at all times, unless you are completely draining it for long-term storage. This will help prevent moisture and rust from forming in the tank.
One recommendation passed down from our grandfathers is to drain the carb after each use. Turn off the fuel valve, and let the engine suck all the fuel out of the fuel system until it dies. This practice may never have been a good idea for anything except long-term storage. With today's ethanol blended fuel, the residue left in the system after each draining quickly dries and leaves deposits. Draining the system frequently will cause those deposits to quickly build up clogging filter screens and passages.
FUEL STABILIZERS: I use the Sta-Bil fuel stabilizer product in my generator, and and fuel storage tanks that will sit for more than a couple of months. The current Sta-Bil products have been reformulated to work well with ethanol-blended fuel. Please, Read the label! Make sure the product is correct for the fuel you have, and you are using the correct amount.
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