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I have found that I have an issue nearly identical to this one:
http://www.thegsresources.com/_forum/showthread.php?247591-1980-gs550e-fuel-tap-tank-noise
The noise is no doubt caused by fluctuations in vacuum (I may have a separate issue here). When I put a tee in the vacuum line and attached a gauge I could watch the needle bounce in time with the tapping. Disconnect vac....tapping stops.
I did a little experiment using a 1/4" check valve in the vac line to try countering the fluctuations. It stopped the tapping, but also stopped the bike about a mile down the road when the internal components of the plastic, aquarium grade check valve melted and fused together from contact with the gasoline leaking through the diaphragm. No vac, no fuel, no go. I knew this might happen but my experiment was a success as far as testing the effect of a check valve in the vac line.
When I opened up the original petcock the diaphragm looked fine, but when held up to a bright light it looked more like a fine mesh screen rather than a rubber sheet. I have no idea if the tapping ruined the diaphragm or if the bad diaphragm led to the tapping. Something I found interesting is the lack of a large washer next to the diaphragm like the one in the post linked above that the poster found in two pieces.
I had already ordered a rebuild kit before I read enough on this site to learn that petcock rebuild kits are a gamble. Already ordered, already paid for, I'll take my chances. Kit shows up in the mail with a diaphragm that is noticeably smaller than mine. Not gonna work. I chalked this up to the reported unreliability of petcock rebuild kits and ordered a whole new OEM petcock.
Finally got the new petcock and went to install. That's when I discovered that my tank has 45mm (44mm?) mounting holes while the new petcock has 50mm holes. I verified part numbers and confirmed that I was sold a petcock that is supposed to fit a 1980 GS550E. It doesn't fit mine.
Do I have a different year tank? The bike was made in November of 1979...could it have a mixture of model year parts on it? I have a 1974 Chevy truck on which I have learned (the hard way) that it was built with some parts from 1973. Chevy changed the design of the blower motor mid-production and some
Here are both petcocks side by side. My original has a selector switch with ON/RES no prime. The new one has no selector, no reserve and has the slotted screw type prime setting.
both petcocks.jpg
http://www.thegsresources.com/_forum/showthread.php?247591-1980-gs550e-fuel-tap-tank-noise
The noise is no doubt caused by fluctuations in vacuum (I may have a separate issue here). When I put a tee in the vacuum line and attached a gauge I could watch the needle bounce in time with the tapping. Disconnect vac....tapping stops.
I did a little experiment using a 1/4" check valve in the vac line to try countering the fluctuations. It stopped the tapping, but also stopped the bike about a mile down the road when the internal components of the plastic, aquarium grade check valve melted and fused together from contact with the gasoline leaking through the diaphragm. No vac, no fuel, no go. I knew this might happen but my experiment was a success as far as testing the effect of a check valve in the vac line.
When I opened up the original petcock the diaphragm looked fine, but when held up to a bright light it looked more like a fine mesh screen rather than a rubber sheet. I have no idea if the tapping ruined the diaphragm or if the bad diaphragm led to the tapping. Something I found interesting is the lack of a large washer next to the diaphragm like the one in the post linked above that the poster found in two pieces.
I had already ordered a rebuild kit before I read enough on this site to learn that petcock rebuild kits are a gamble. Already ordered, already paid for, I'll take my chances. Kit shows up in the mail with a diaphragm that is noticeably smaller than mine. Not gonna work. I chalked this up to the reported unreliability of petcock rebuild kits and ordered a whole new OEM petcock.
Finally got the new petcock and went to install. That's when I discovered that my tank has 45mm (44mm?) mounting holes while the new petcock has 50mm holes. I verified part numbers and confirmed that I was sold a petcock that is supposed to fit a 1980 GS550E. It doesn't fit mine.
Do I have a different year tank? The bike was made in November of 1979...could it have a mixture of model year parts on it? I have a 1974 Chevy truck on which I have learned (the hard way) that it was built with some parts from 1973. Chevy changed the design of the blower motor mid-production and some
Here are both petcocks side by side. My original has a selector switch with ON/RES no prime. The new one has no selector, no reserve and has the slotted screw type prime setting.
both petcocks.jpg
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