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  • Title Page- Servicing the petcock
  • Original Author- Chuck B

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Servicing the Petcock on your Valkyrie:

The Petcock is quite simple in its construction and operation. A correctly operating petcock on the Valk will only allow fuel to flow when vacuum is applied (Small hose attached) no matter what position the petcock is in. The "Off" position will not allow fuel to pass even with vacuum. This allows removing most of the fuel from the bowls, if needed, by letting the bike burn it off while running. However, for storage purposes Iíd go a step further and use the drain plug at the bottom of each bowl. My other bike does not have an "OFF" position but rather a "Prime" or always on position. All vacuum operated petcocks operate basically the same.

Once you get the tank off set it down on something soft. Pickup the rear and roll it up on its nose. It will sit there and allow you to remove the petcock without spilling gas. However, when you set the tank back down flat hold your finger over the vent tube or gas will begin to siphon out. (Makes a neat looking fountain!) Remove the petcock by loosening the flange nut. Carefully pull the petcock out. Youíll see the fuel screen attached, which is in two sections, one for "On" and the lower portion for "Res". Mine had material all over the reserve portion and the lower section of the upper portion. (Did that make sense?) I have a solvent tank, which I have filled with a mild contact cleaner. Basic Carb. Cleaner would work. Just be careful with the screen, its very delicate.

The rest of the petcock is made up of three sections. The 1st is the main unit which has the screen attached to. The 2nd and 3rd pieces are attached to the main section with 4 Phillips screws. The outer section is just a cover. The middle section holds the diaphragm. Notice that this section has a small nipple protruding which has a hole in the center. This is a check valve. Remember which direction this is facing in relationship to the main section. There is a spring between the cover and diaphragm. This spring pushes the diaphragm back when vacuum is released and prevents fuel from flowing. Also note when you pull the cover off and remove the spring (Donít let it fly away!) The rubber diaphragmís larger section faces outward. Clean everything with your cleaner and reassemble. Make sure you VERY carefully pull the ends of the diaphragm up and clean behind and between the folds. If for any reason the middle section will not pull away from the main section DO NOT force it. It simple means your check valve is plugged and vacuum is holding it on. Thatís why when you disconnected your fuel line gas continued to flow until you turned your petcock to the "Off" position. Just carefully lift up on the end of the diaphragm to release pressure. That was one of the problems with my petcock.

Now that it is all back together. Its time to test it to ensure it works properly and wonít require pulling the tank back off later. Simply attach a (Clean) rubber hose onto the vacuum nipple. Apply a slight vacuum to the hose while looking down the fuel outlet. Yes, your mouth works great for this! Just donít suck very hard. Itís very easy to overcome the spring tension. As you apply vacuum/suction youíll see the diaphragm pull away from the main section. When you release vacuum/suction the diaphragm will SLOWLY return sealing off the flow of fuel. If it does not either you assembled incorrectly or your check valve is still clogged or defective. If all works, youíre done!

Hope this helps!   Chuck B

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