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1985 VT500C won't start when hot

8846 Views 48 Replies 10 Participants Last post by  David C.
I bought this bike back in Feb. of this year. It had a bad rod knock, so we tore it down and replaced the crankshaft, push rods, and push rod bearings. It is running fine. I can start it, drive it wherever I want to go, but if it's hot, it does not want to re-start. After a bunch of reading here, I decided that the fuel system might be creating a vacuum, so I started poking around. I noticed that the fuel shutoff valve has this vacuum line;

The new fuel shutoff valves do not have the vacuum line;

Honda Shadow Aero Sabre Spirit 1100 Ace Tourer Gas Fuel Tank Petcock Valve | eBay

Does anyone have experience with this problem, or should I be checking another part of the fuel system?
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The vacuum line on your existing petcock opens the valve automatically when the engine is running and closes it when the engine shuts off. This will keep the carbs from filling your crankcase with gas if a float valve doesn't seal.

The petcocks you're looking at on Ebay are not for your bike. They're for bikes with fuel pumps (as opposed to gravity feed like your bike). The pump won't allow fuel to continually drain if a float valve goes bad, so the vacuum operation isn't necessary.
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