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--- techtalk:evo:body02 [2020/04/14 02:59]
ixl2relax [FUEL TANKS]
+++ techtalk:evo:body02 [2020/07/01 18:39]
ixl2relax [Petcock (Fuel Outlet)]
@@ Line 77: / Line 77: @@
 ===== Petcock (Fuel Outlet) =====
+The Petcock allows control of the fuel to the carburetor from the fuel tank. It has a 3-position lever to allow OFF, ON & RESERVE settings. The **OFF** settng prevents fuel flow to the carb. The **ON** setting allows normal fuel flow to the carb when the tank is above the reserve level. The **RESERVE** setting allows the final amount of fuel to be sent to the carb until the tank is empty. Normally, the petcock has an in-tank cylindrical mesh filter enclosing these inlets to prevent any dirt in the tank from clogging the intake of fuel. The tank and filter may be required to be cleaned from time to time.
+The petcock creates two levels of fuel supply in the fuel tank, the higher level being used for the 'ON' setting and a low level being used for the 'RESERVE' supply level. To do this, a short tube protrudes vertically into the fuel supply to create an 'ON' level. A shorter tube (or the base of the petcock) is used to supply fuel ONLY when the petcock is set to 'RESERVE'. By drawing fuel from the taller tube when the petcock is set to 'ON', a 'reserve' is created (usually between 20% & 30% of the tank size) below that tube level so as to warn the rider that the tank is running low on fuel.
+When the fuel level drops below the level of the taller 'ON' tube, the engine will sputter or die. The rider needs to switch to the 'RESERVE' setting in order to use the final amount of fuel in the tank (and get to a fuel station before running out completely).
 {{:techtalk:evo:body:petcock_function_1_by_hippysmack.jpg?direct&300|}} ((drawing by Hippysmack)) \\
+In 1992, when there was an option for a 3.25gal Sportster tank, the petcock supplied was a new, vacuum-operated design. It had an automatic shutoff function that used a vacuum hose connected to the carburetor (tee'd off the hose to the VOES) to operate a diaphragm in the petcock. This diaphragm had a short plug that protruded into the fuel flow cavity, and held there by a spring, to prevent fuel flow until there was enough vacuum to pull the diaphragm/plug out of the cavity.
+This was considered a safety feature (to help riders who forgot to turn the petcock to the OFF position).
 \\

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