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157 Posts
(this was originally posted by Lance Ostiguy on Yahoo)
I've discovered the petcock actually has 2 valves designed in it. I don't mean the "reserve" or "on" as being the two. There is a simple *check value* located as part of the vacuum tube fitting to the side of the carb. The part you can see as the brass nipple on the bottom of the petcock contains this check value. The check value is there to protect the rubber diaphram in the petcock body from rupturing if the engine backfires (at least this is what I think) and turning you into charcoal. The check valve only works (is open) in one direction, a vaccum. Perhaps, these valves don't function properly with the safety device built into the petcock whenever the fuel pressure in the tank is low? Maybe it's a combination of dirt/wear too? You may want to look at the valve to see if it works freely? I had my petcock dissassembled and noticed I could open the check valve when vacuum was applied to the brass nipple. BTW- No I'm not going to admit to sucking on it. That info is private and only for me and my bike! hehe. Anyways, if
you blow into the nipple you can see that the check valve loses
and no air will pass by it (towards the rubber diaphram). If you're not familiar with check valves, people who have aquariums and air pumps can help you. But it's very simple. A spring and plunger is all what it is. Perhaps the plunger is jammed or sticking at times, thereby shutting off the vacuum to the petcock and gas to the carb bowls. As a simple fix, try shooting some WD40 or such, into the tiny hole in the brass nipple using the red thingy after taking the vacuum tube off. I WOUNLDN'T suggest you discard or bypass the valve altogether, because you're bike might turn into a ball of flame if the engine should backfire, etc.
I've discovered the petcock actually has 2 valves designed in it. I don't mean the "reserve" or "on" as being the two. There is a simple *check value* located as part of the vacuum tube fitting to the side of the carb. The part you can see as the brass nipple on the bottom of the petcock contains this check value. The check value is there to protect the rubber diaphram in the petcock body from rupturing if the engine backfires (at least this is what I think) and turning you into charcoal. The check valve only works (is open) in one direction, a vaccum. Perhaps, these valves don't function properly with the safety device built into the petcock whenever the fuel pressure in the tank is low? Maybe it's a combination of dirt/wear too? You may want to look at the valve to see if it works freely? I had my petcock dissassembled and noticed I could open the check valve when vacuum was applied to the brass nipple. BTW- No I'm not going to admit to sucking on it. That info is private and only for me and my bike! hehe. Anyways, if
you blow into the nipple you can see that the check valve loses
and no air will pass by it (towards the rubber diaphram). If you're not familiar with check valves, people who have aquariums and air pumps can help you. But it's very simple. A spring and plunger is all what it is. Perhaps the plunger is jammed or sticking at times, thereby shutting off the vacuum to the petcock and gas to the carb bowls. As a simple fix, try shooting some WD40 or such, into the tiny hole in the brass nipple using the red thingy after taking the vacuum tube off. I WOUNLDN'T suggest you discard or bypass the valve altogether, because you're bike might turn into a ball of flame if the engine should backfire, etc.