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Old November 26th, 2019, 07:52 AM   #1
Detrailers
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Name: Jeff
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Petcock

Greets all,
The petcock that was on my bike was definitely aftermarket and broke. The first one I replaced it with wouldnt operate via the vacuum port so it wouldnt draw fuel. I had a brand new gravity feed one here and installed that and plugged the vacuum port on the carb.
Came out the next a.m. to a puddle of fuel coming from the carbs. When I cleaned out that carbs I check the floats, needles and even tested them to make sure they were sealing.
Is the gravity feed too much for the float needles to handle?
Going back to vacuum petcock today with fingers crossed
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Old November 26th, 2019, 02:35 PM   #2
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Originally Posted by Detrailers View Post
Greets all,
The petcock that was on my bike was definitely aftermarket and broke. The first one I replaced it with wouldnt operate via the vacuum port so it wouldnt draw fuel. I had a brand new gravity feed one here and installed that and plugged the vacuum port on the carb.
Came out the next a.m. to a puddle of fuel coming from the carbs. When I cleaned out that carbs I check the floats, needles and even tested them to make sure they were sealing.
Is the gravity feed too much for the float needles to handle?
Going back to vacuum petcock today with fingers crossed
Back when I was a kid learning riding my grandfather was repeating it multiple times. Engine off - petcock into the off position Never leave it open for long times.

Having said that I did test mine in on position for an hour or so and it was not leaking.
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Old November 26th, 2019, 05:53 PM   #3
Detrailers
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Originally Posted by SibSerge View Post
Back when I was a kid learning riding my grandfather was repeating it multiple times. Engine off - petcock into the off position Never leave it open for long times.

Having said that I did test mine in on position for an hour or so and it was not leaking.
Because you probably have a vacuum operated one
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Old November 26th, 2019, 06:22 PM   #4
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Because you probably have a vacuum operated one
Mine has 3 positions ON , Reserve both vacuum operated and PRI (priming). The latter is free flowing. I tested in PRI . Actually the first week after I bought my bike it was sitting in PRI position all the time until I learned what it was.

I still feel a bit uncomfortable having a petcock that does not have the off function as this is what I used to. We will see how it goes. I will probably rebuild it sooner than later as the bike is 12 years old and I have no faith in the rubber holding well after such a long time.
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Old November 26th, 2019, 06:43 PM   #5
Detrailers
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Originally Posted by SibSerge View Post
Mine has 3 positions ON , Reserve both vacuum operated and PRI (priming). The latter is free flowing. I tested in PRI . Actually the first week after I bought my bike it was sitting in PRI position all the time until I learned what it was.

I still feel a bit uncomfortable having a petcock that does not have the off function as this is what I used to. We will see how it goes. I will probably rebuild it sooner than later as the bike is 12 years old and I have no faith in the rubber holding well after such a long time.
Weird because if I turn the carbs upside down and push up the floats the needle seal and I cant blow air thru the intake. Hopefully the vacuum petcock will help thia
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Old November 26th, 2019, 07:45 PM   #6
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I just did a very rough ballpark calculations and based on that in the best case scenario (carbs are level the the bowl is full) to overcome the pressure of the float on the valves one needs about 28psi of pressure (2kgf/cm2) . Gasoline in when it is not blocked by petcock only creates around 0.56psi which is way too low to open the valve.

And if you think about it even for bikes with a petcock opened by the vacuum the petcock state is equivalent to open state of a regular petcock yet the mixture is not affected bu the petcock. If valves could not hold the gasoline back then the mixture would be affected by petcock that is it will be modulated. The card would not work properly ever. It would be impossible to tune.

You might need to inspect the valves - they might have imprints on the rubber which will not align to the edge of the valve and will cause the leak. Worse yet the orifice could be damaged or there could simply be some debris.

I do not think you can detect this kind of conditions with blowing the air. The leak could be very minor to be detectable by air blow. Yet over many hours it will let enough liquid through to be noticeable
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Old December 3rd, 2019, 08:14 AM   #7
Detrailers
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^^^^^^that is exactly what is was, a ever so small leak from one of the float needles. It also was causing a second issue with idling because bike would start up and run fine, and unbeknownst to me was leaking extra fuel into one of the cylinders and then the motor would idle rough and die, and then be hard to start bc 1 cyl flooded.
Fixed and runs like a champ now.
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Old December 3rd, 2019, 11:01 AM   #8
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Originally Posted by Detrailers View Post
^^^^^^that is exactly what is was, a ever so small leak from one of the float needles. It also was causing a second issue with idling because bike would start up and run fine, and unbeknownst to me was leaking extra fuel into one of the cylinders and then the motor would idle rough and die, and then be hard to start bc 1 cyl flooded.
Fixed and runs like a champ now.
Glad it works now !
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