Fuel Gauge Float & Send Unit

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The fuel system on my bike consists of the tank itself, the float and send unit for the gas gauge, and the petcock (or fuel tap).

Here's the underside of my fuel tank. You can see the opening for the petcock in the lower right, as well as the fuel gauge send unit. The float is inside the tank pointing away from the petcock. The two wires connect to the fuel gauge by your handlebars. The hose port in the send unit is a drain. The hose runs down below the frame of the motorcycle and is open to the atmosphere. It's a safety device in the event that the send unit gasket leaks. The leaked fuel will drain to the ground instead of on your electrical parts, engine, and/or frame.

Bottom of fuel tank

When the tank is full, the float will be physically high in the tank and the resistance will be low. When the tank is empty, the float will be low in the tank and the resistance will be high.

To check if the float and send unit are working, one can measure the resistance (in ohms) across the two wires with the tank, emptied of fuel, right side up (simulating an empty tank) and upside down (simulating a full tank). The resistance should move smoothly between roughly 10 ohms (full) and 100 ohms (empty).

If the circuit path is open, the resistance isn't smooth, or you just feel like it, you can open up the send unit and remove it from the tank. First, remove the four cover screws.

Removing send unit cover

It seems some sort of insect crawled up the drain hose and made itself a nest inside. I'll have to clean out the drain hole. Next, remove the 5 bolts holding the unit itself to the tank. They are 8 mm hex.

Removing send unit

Be very careful getting the float out. You'll need to move it around and find the right angle to allow it to be removed. The gaskets are rubber and come right off.

Send unit removed

On the side with the float arm, there's three tabs that you have to bend open to remove the cover.

Tabs on cover

You can see the float arm and the two metal contacts, one of which moves with the float arm. Here it is down:

Float arm contact down

And up. Notice the position of the contact. The contact may have to be bent back in if there is a gap.

Float arm contact up

Measuring the resistance now. 118 ohms when the arm is down for an empty tank.

Resistance arm down

And 13.2 ohms when the arm is up for a full tank.

Resistance arm up

Mine seems to be working well. I'm gonna clean the contacts up anyway. The gaskets can be reused since they are rubber, unless they are ripped or otherwise damaged. The bolts do not need a high torque at all; snug is good enough. Be careful not to strip the threads.

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