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post #1 of 3 (permalink) Old 09-04-2005, 03:24 AM Thread Starter
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Question inspection of fuel valve

after a week my 750 had been parked in my garage with a fresh tank of 87 octane . the bike ran great at shut off time . today i decided to take a spin . turned on gas valve and cranked her over---- nothing . cranked and cranked. smelled no fuel . checked for spark is good all wires. disconnected fuel lines from carbs with gas valve on , no gas flow. ok ,then proceeded to remove fuel valve ,removed fuel tank etc. thought i'd find a load of crap in filters but they were clean as a whistle as was the rest of the valve . reassembled and tried starting again. no start.i lossened a carb boot and squirted a little gas in the carb. started right up .runs fine again. question is ; after a weeks time is it possible the carbs went dry and because the vacuum diaphram needs replacing caused no flow to carbs. hard to believe this is normal to get the flow going fuel needs to be squirted in carbs to start up.does anyone have or had this problem.trying to avoid getting stranded if this happens away from home. replies needed ,thanks, ken smith
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post #2 of 3 (permalink) Old 09-04-2005, 10:19 AM
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Re: inspection of fuel valve

What do you use for the initial starting procedure?
Usual is full choke,. no throttle. A maintenace free battery helps weak starts and I have never turned the fuel valve "off" I leave it in the on position and have had no problem with fuel leakage. That fact that you did get it started after spraying the bowls would indicate that the battery was fine though.
Perhaps leaving the gas on does help keep a little gas in the bowls, which depending on the heat may have evaporated. Our bike seems slow to switch over to new delivery, atleast when switching from on to reserve. Perhaps the same is true when switching from off to on.
What you went through to start sounds like the start up procedure after bringing the bike out of winter storage. You had to "prime" the fuel system first before it would start.
Try it next time leaving the gas petcock turned on and see if there is still a problem.

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post #3 of 3 (permalink) Old 09-05-2005, 03:22 AM Thread Starter
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Question Re: inspection of fuel valve

thanks for reply D ; i have left the valve in the on position and will see if it starts right up monday . i still would like to know exactly how the valve functions in regard to the vacuum and diaphram set theory was the vacuum prevents an igniting of the fuel into the fuel tank in case of a back fire from the carbs, by closing off air to the my doubts about that but could be wrong. another thought is the vacuum helps draw the fuel to the carbs,but then if that is true wouldn't the vacuum while cranking in an attempt to start produce enough vacuum to fill the carbs.does anyone have an explanation of the operation of this vacuum and what is the purpose of it??the shop manual says if fuel flows out of fuel valve in the on or res. position with engine off you need to replace the damaged ''o'' ring or gasket.this is why i think the vacuum created causes the fuel to flow to carbs. i'm still confused to what happened when i tried to start my vn after sitting for a week and it seemed to have lost its prime . started when i squirted gas in carb . any ideas? thanks for reply ken smith ps. filters found to be clean and no leakage at valve. also i have a new mf battery and use full choke no throttle on start procedure.
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