Okay, I know HOW to use the reserve tank on the rider mower, the switch is under the seat (see picture).

What I don't understand is HOW the fuel gets into the reserve tank and, most importantly, if I don't occasionally use the fuel in the reserve, won't it get stale and how was the tank intended to be used? Whenever the the primary goes dry?

Edit: Added picture (as I meant to). Model number is 917.204010 (Crafstman 48" mower manual) (I really miss my old Crafstman that was dead simple and I could just look down and see how much gas was left in the tank)

Crafstman 917.204010

2 Answers 2


After having look at a page from an owners manual for one of these ride-on mowers, I would say that the reserve is just an outlet on the main fuel tank lower down in the tank than the main fuel outlet.

Example of a motorbike reserve valve -

This means that there is no need to worry about filling the reserve tank, or the fuel going stale, because the fuel is mixed each time you fill up.

The 'reserve' fuel just gives you enough to possibly drive the mover back to your shed to refuel if you run out while mowing.


It would be useful to have identifying information for your mower. Sears uses long strings of digits to provide specific model information.

Barring that, it's certainly likely that your mower has what was common on motorcycles and very early model Volkswagen Beetle automobiles.

The fuel lever in the normal position would drain fuel to a certain level, leaving some fuel in the tank. When turned to the reserve position, a port in the tube would open at a lower level, providing this "emergency" fuel to get home.

The website engineermind.in has a simplified explanation, image below from linked site:

reserve fuel lever image

This particular image does not show a single tube, but serves the purpose. Other images exist that have a single tube with two ports for normal and reserve.

Fuel sloshes in everyday use, which means that it won't go stale, as it's constantly mixing.

Your added photos appear to show an inverted version of the diagram. It appears that one of the two options would have a tube that extends almost all the way to the bottom of the tank, while the other option would reach to the bottom.

  • Looks like we found the same picture on the internet. :)
    – HandyHowie
    Oct 9, 2023 at 14:46
  • Added part number and pictures. Oct 9, 2023 at 15:37

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