FUEL FLOW TEST

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Posted by Tim Daley(MI) on November 30, 2020 at 07:00:45 [URL] [DELETE] :

In Reply to: Gas Flow posted by Jack-Iowa on November 29, 2020 at 18:27:37:

Fuel Flow on gravity fed M/S carbs is not based on volume or size of carb. Fuel flow is the same.

The Marvel-Schebler Fuel Flow Test on the N-Tractors has been detailed many times in posts, but I can't recall if I have ever actually read the procedure in any Ford or M/S manual as gospel documentation. Most simply say to remove fuel line from carb inlet and observe fuel flow. Any weak stream or hesitation indicates an obstruction upstream. FWIW & FYI: What has been posted and I'll again post here so the archives can be added:

Find a 1-Pint Mason Jar and place in a coffee can, then position can under the carb. Loosen the 7/16" hex flare nut on the fuel line at the carb brass inlet elbow and gently slide the fuel line off to the side so it points down into the can. Open the Fuel Sediment Bulb Valve 2 Full Turns. Observe the fuel flow is a steady stream and you fill the can with 1 pint in 2 minutes. Any sputtering, hesitation, or failure to fill gas in the Mason Jar indicates the problem is upstream on the Sediment Bulb or in the gas tank itself. If Test passes, connect the fuel line and repeat using the carb drain plug in bottom. This is a NPT plug, tapered pipe thread; it's not a standard thread size, so do not try to use anything other than that to chase threads or replace. Often you see the hex head on the plug all rounded off from guys using pliers, vise gripes, channel locks, or simply the wrong size wrench to remove. Get the right tool. If Fuel Test passes, reset the drain plug, leave it alone, and move on -it's electrical. 99.8% of all non-starting issues are due to electrical. Many fuel issues are due to clogged systems starting with the fuel tank. 75 years of use can collect a lot of sediment, rust, and dirt. The fuel tank also has a vent on the top of it with a very small, 1/32" diameter or so air hole. If this vent gets plugged up it hinders proper fuel flow. Since the tank is not easily accessible, it's fastened to the bottom of the hood and it along with several other parts must be removed along with it so chances are the gas tank hardly ever, if not never, got flushed and vent passage cleared.


Tim Daley(MI)


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