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post #1 of 8 (permalink) Old 07-25-2012, 04:53 PM Thread Starter
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petcock questions

Number 1 - should I be turning this off after every ride? In my intro to motorcycle riding course they said it should be turned off when the bike is off, and I guess it's just slipped my mind every time. Am I in danger of anything like gas overflowing into the oil supply, or will it stay in the fuel line since the pump is not on?

Number 2 - had fuel leaking out of the petcock, which is now resolved since I tightened the fuel line from petcock to pump. So the petcock, even when turned off, does not seal shut. Note: leaks from the nipple that the fuel line connects to. Rather than buy a whole new unit, can I just replace the insides? Looks like there's a rubber o-ring and another round rubber gasket with holes to control the fuel flow... are these the most likely culprits?

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post #2 of 8 (permalink) Old 07-26-2012, 07:40 AM
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My '94 had the same problem, "off" would still allow a trickle of gas through and I had, at the time - now fixed, a leaking carb gasket leaving a few drips to collect on the floor. I found a damaged rubber seal in the petcock and carefully made a replacement from some rubber sheet stock. I also found a match for the O-ring at a hardware store. Now "off" is OFF! I use off when I put the bike in the shed but not during a ride. I could send you a piece of that rubber if you wanted to try making one.
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post #3 of 8 (permalink) Old 07-26-2012, 08:00 AM Thread Starter
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Alright - I'll try and start remembering to switch it off. Thanks for the offer on the rubber piece, but I went ahead and ordered one today - $7 including shipping and an o-ring. I have a whole case of o-rings, but somehow things like this always end up being a non-standard size.

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post #4 of 8 (permalink) Old 07-26-2012, 09:00 AM
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I am not sure what the best practice is... I guess if you are a regular rider turning it "off" every time is probably not required... if you are doing long term storage and run the carb dry then turning it off probably makes sense to be sure nothing is getting thru...

Certainly fixing any leaks just makes sense and you should do that... hth...

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post #5 of 8 (permalink) Old 07-26-2012, 04:09 PM
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From what I read aboout the guys with the fuel petcocks, if it is not turned off and you are not riding in an hour or so gravity forces fuel down the line and causes problems. As a kid all bikes had petcocks then, I just turned mine off when I got to school or when through for the night. If I stopped for a burger I just left it alone.

Just my $.02

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post #6 of 8 (permalink) Old 07-30-2012, 09:28 PM
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I have never turned mine off....
with that said...ethanol spiked gas WILL RUIN a carb in a very little time. It is a rubber solvent and it is is a plastic solvent'. The boating industry is already well aware of the damage it can cause. I think at the end of the season then turn you petcock off and run the gass in your carbed engine dry...and dump what you have left in the tank! If it leaks then fix it. That is not a too hard job.

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post #7 of 8 (permalink) Old 07-30-2012, 09:59 PM
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The risk of leaving the petcock on is a potential hydrolock. If all the conditions are right, a carb could leak, filling a cylinder full of fuel. Fuel doesn't compress like air does, so when the cylinder comes up, if it happens to be on the compression stroke, it could slam up against a wall of fuel and bend a rod, damage the starter, do any number of damages. It could also gum up if left on for long periods.

That situation isn't likely, but it is possible!

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post #8 of 8 (permalink) Old 07-31-2012, 05:42 AM
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Unlikely?

Quote:
Originally Posted by Romans5.8 View Post
The risk of leaving the petcock on is a potential hydrolock. If all the conditions are right, a carb could leak, filling a cylinder full of fuel. Fuel doesn't compress like air does, so when the cylinder comes up, if it happens to be on the compression stroke, it could slam up against a wall of fuel and bend a rod, damage the starter, do any number of damages. It could also gum up if left on for long periods.

That situation isn't likely, but it is possible!
Possible but very unlikely. Piston rings aren't capable of a 100% seal. Fuel would really have to pour through the carb, intake, valve combo to get into the cylinder faster than it can leak past the rings. It is a common occurance to have a crankcase get contaminated with fuel from exactly that. If you have a manual valve, get in the practice of turning it off. If you have a vacuum actuated petcock I'd recommend that you check it a couple times per season. I had mine leak overnight and the fuel did leak into the oil and overfilled the crankcase with a fuel / oil mix. A mess to clean out and expensive to dum the oil and flter plus the cost of a petcock. They seem to have about a 3 year life before needed a rebuild or replacement.



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