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Discussion Starter · #1 ·
Bought a 83 shadow 500 been setting up a while cleaned carbs getting fuel to carb spark has good compression seems gas not making it to cylinder any suggestions
 

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1983 Honda vt750 Shadow
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Loosen the carb bowl drain screws to see if 1 or 2 ounces of fuel runs out of each.
If it does, there is fuel available inside, but the float level is not right or the jets are still plugged.
 

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'83 VT750C
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Does it run with a little gas put directly into the cylinders? You may have to clean the carbs out… again.
 

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Discussion Starter · #5 ·
Does it run with a little gas put directly into the cylinders? You may have to clean the carbs out… again.
Can’t find a petcock for the bike cleaned carbs again tried using two petcock to make one that’s my problem starving for gas any suggestions where to get new one everybody saying Honda quit making them.
 

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'83 VT750C
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Any reason why it has to be vacuum-operated? It’s just a valve, after all. Heck, you could even eliminate it. It’s just handy to cut off fuel flow when doing any work downstream of the tank, or if a float bowl or something were to fail… I don’t think my father ever turned his off.
 

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Well, no, but a regular (or no) petcock would allow full flow at all times, rather than being restricted by vacuum pressure. Unless that doubles for a vacuum operated pump as well…
 

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Discussion Starter · #10 ·
Well, no, but a regular (or no) petcock would allow full flow at all times, rather than being restricted by vacuum pressure. Unless that doubles for a vacuum operated pump as well…
That’d be my understanding anyway thanks for your help
 

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'83 VT750C
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I did some quick research, and it is more of an ‘on/off‘ thing with the vacuum. Gravity and suction from the carbs does the rest, since the 500 doesn’t have a fuel pump, AFAIK.
 

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Discussion Starter · #12 ·
Well, no, but a regular (or no) petcock would allow full flow at all times, rather than being restricted by vacuum pressure. Unless that doubles for a vacuum operated pump as well…
I’ve looked everywhere on internet only petcock I can find is 18mm my fitting on my gas tank is smaller than that taking a pair of calipers home today to measure to see exactly what size I need would like to find new one but may have to rebuild old one any suggestions would be greatly appreciated.
 

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Buy a replacement petcock?


If it is the vacuum diaphram that is the issue, I've read somewhere here in the forum that this valve can be placed mechanically into the "ON" position by disassembling and removing a spring and/or putting a spacer inside that prevents the vacuum valve from shutting off.

The vacuum valve is there for safety. If the bike is in an accident and the engine stops running, the fuel flow will stop, a nice feature if your leg is trapped underneath it, and a nuisance at every other point in time.
 

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2001 Valkyrie I/S
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If your having vacuum problems with your petcock you can order a new cover set for your ride here.
Your petcock doesn't act as a pump you have a gravity feed system. If the diaphram leaks on the petcock it may not open all the way. If you have a vacuum leak in one of your hoses it may not open all the way. Make sure you have good vacuum first then pull out the diaphram and see if it's cracked.
 

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Discussion Starter · #15 ·
Thanks everyone got fuel through petcock she runs sending tank and rear fender out for paint thanks again for you guys help.
 

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'83 VT750C
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Great! Was going to say the sizing of the petcock isn’t critical, though a little bigger is better than a little smaller. Enjoy the rest of the season!
 
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