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Discussion Starter · #1 ·
Hello BLKBIRD world. I just picked up a 97 BB that a guy bought out of storage unit. He said he cant get fuel to carbs because he couldn't find the pump or relay. I know it has a vacuumed petcock so I rebuilt it. I can pour fuel in the carbs and the bike fires up. If I pour down the fuel lines to fill the bowls it acts like its starving for fuel. How much vacuum pressure is needed to operate the petcock?
 

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Hello BLKBIRD world. I just picked up a 97 BB that a guy bought out of storage unit. He said he cant get fuel to carbs because he couldn't find the pump or relay. I know it has a vacuumed petcock so I rebuilt it. I can pour fuel in the carbs and the bike fires up. If I pour down the fuel lines to fill the bowls it acts like its starving for fuel. How much vacuum pressure is needed to operate the petcock?
I have a 98 BB, and initially the vacuum pipe wasn't fitted, yet it stilll rang ok. I refitted prop-let and It did start to get lumpy at 8k in 6th bit like the rev limiter was cutting in and also 2-4k was lumpy but above was great. iN THE END FOUND OUT THE diaphragm in the petcock was ruptured. Replaced it and it been amazing since. Have you checked if any fuel dripping out of bottom petcock pipe? It was that which pointed to ruptured diaphragm.
 

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Discussion Starter · #3 ·
Thanks Fluff. When I got the bike there was fuel dripping out the bottom nipple. I replaced the diaphragm but gas just trickles out the fuel lines when turning the bike over. Disconnected the vacuumed line and turned it over and there was barely enough to suck my finger over the hole. Wondering how much vacuum pressure needed to suck the diaphragm to allow more fuel to flow.
 

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Thanks Fluff. When I got the bike there was fuel dripping out the bottom nipple. I replaced the diaphragm but gas just trickles out the fuel lines when turning the bike over. Disconnected the vacuumed line and turned it over and there was barely enough to suck my finger over the hole. Wondering how much vacuum pressure needed to suck the diaphragm to allow more fuel to flow.
When I disconnected my fuel, even after turning off the fuel tap, quite a lot of fuel came out of fuel hoses. If your not getting a lot come down your fuel pipes maybe you got a block inside the tank or pipes, especially as been standing so long?? Have you flushed out your tank? As said mine ran ok even without the vac pipe on so can't make that much of a difference?? Also you def fitted a spring when you put Petcock and diaphragm together?
 

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Discussion Starter · #5 ·
Drained old gas and sprayed inside of tank with carb cleaner and then blow out with air compressor. With fuel lines unhooked and petcock open without vacuum line nothing comes out. With vacuum attached and turning it over fuel just trickles out. Thinking about removing the diaphragm and see how the bike runs that way or will it allow to much fuel to the carbs?
 

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Doesn't take much vacuum to operate the petcock. Fuel should flow out in a nice steady stream. Have you removed the fuel tap assembly to see what condition the fuel strainer/filter is in?
Replace the vacuum line, there may be a tiny hole causing an air leak.
 

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Discussion Starter · #7 ·
Thanks Wood. The strainer is all clean. checked that when I did the petcock. I am going to replace both fuel lines and the vacuum line as well since they are hard. Going to pull the carbs off tomorrow and see what the insides look like and clean as well.
 
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