If you are like me you want a nice manual petcock but don't want to pay much for it. The solution is to buy a metric to imperial adapter plate and a Harley petcock, total cost is 26 CDN before tax! That was less than the price of a rebuild kit for my Suzuki petcock. I bought an adapter plate from MAC (MC Distributing) that has two mounting holes at 44 mm centre to centre for my '81 GS1100EX. The plate has a 3/8" NPT bung hole that is common to Harleys up to about '73. 
Here we are, the MAC plate comes with a rubber gasket, 2 rubber washers, and two metric allen key bolts. The plate is quite thick so the allen heads are countersunk. The filter on the petcock I chose was round so I had two options. Evactuate the fuel tank and modify it or remove the filter. I removed the filter and placed one inline. One more thing I should note is that the tap I bought has a smaller outlet. It's about 3/16" internally vs. the 1/4" of the stock tap. The pickup tube is an amazing 3/32" ID but my bike runs well with it. With 115 main jets I can hit 7000 RPM in 5th gear which is no different than what my bike could do with the Suzuki tap set to prime. The only problem I've had is that it takes a long time for the reserve to return your bike to full power due to the small pickup tubes. On the 1100EX I hit reserve after burning 14 litres of fuel. That leaves me with another 5.
The petcock has to be turned inward a bit for the fuel line to pass the carberetor. Forward for prime, down for on, back for off.
Steve
Here we are, the MAC plate comes with a rubber gasket, 2 rubber washers, and two metric allen key bolts. The plate is quite thick so the allen heads are countersunk. The filter on the petcock I chose was round so I had two options. Evactuate the fuel tank and modify it or remove the filter. I removed the filter and placed one inline. One more thing I should note is that the tap I bought has a smaller outlet. It's about 3/16" internally vs. the 1/4" of the stock tap. The pickup tube is an amazing 3/32" ID but my bike runs well with it. With 115 main jets I can hit 7000 RPM in 5th gear which is no different than what my bike could do with the Suzuki tap set to prime. The only problem I've had is that it takes a long time for the reserve to return your bike to full power due to the small pickup tubes. On the 1100EX I hit reserve after burning 14 litres of fuel. That leaves me with another 5.
The petcock has to be turned inward a bit for the fuel line to pass the carberetor. Forward for prime, down for on, back for off.
Steve
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