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yep as been said a few times, always turn the fuel tap off with the engine, as a bike mechanic ive seen many many float valves fail and fill the crankcase full of petrol.
I had a CBR900RR, one morning went out to head off to work. I had forgotten the petcock, which I normally always turn off on all my bikes. Ign on, hit the button, nothing, no crank, what the hell? Ok, off I wne on the truck. Got home, took a look, smelled a little fuel, what the hell? Don;t recall how it all went but the bike on the side stand, the left cylinders were full of fuel, full. The float seat let fuel leak past and instead of overboarding to the ground like I have had other bikes do when they tell you the float needle is failing, the fuel went into and locked the cylinder. I love carb bikes, prefer them over EFI, but you have to treat them differently. Like a high-strung wife or GF, over a Mary Poppins wife or GF. Just my 2 cents, your situations may vary and garages survive differently....
I had a CBR900RR, one morning went out to head off to work. I had forgotten the petcock, which I normally always turn off on all my bikes. Ign on, hit the button, nothing, no crank, what the hell? Ok, off I wne on the truck. Got home, took a look, smelled a little fuel, what the hell? Don;t recall how it all went but the bike on the side stand, the left cylinders were full of fuel, full. The float seat let fuel leak past and instead of overboarding to the ground like I have had other bikes do when they tell you the float needle is failing, the fuel went into and locked the cylinder. I love carb bikes, prefer them over EFI, but you have to treat them differently. Like a high-strung wife or GF, over a Mary Poppins wife or GF. Just my 2 cents, your situations may vary and garages survive differently....
yeah i prefer carbs over EFI, my 2006 dyna has a carb conversion with an ON/OFF fuel tap, ive even converted bikes with a vacuum tap to a manual tap as the vacuum taps can also fail and leak fuel into the engine.
Manual petcocks are fine by me. Carbs, too. The old ways were good enough. And yeah, other than a ten minute break I turn them off. Having a reserve was nice also.
When was the last time you inspected your fuel line?
Mine rotted out from the inside from the ethanol gas and pieces
got into the float, holding the needle open.
That's how I found I had a rotted hose, gas was leaking into the engine.
Luckily the wife had gone into the garage about 10 minutes after I got home and told me she smelt gas.
I guess I've been lucky, all of these years. Whenever I go out to the garage and see I've left the valve open, I just shrug and say, "oops". It's happened so often, I just don't freak out. Like I said, it should be checked to make sure it is shut off, if you're going to leave it sit. I've only rarely heard of this problem with others, but their bike's age or condition seemed to be half of the problem. My Sportster is an 06, but the lines and valve are a lot newer than that!
I just have never had that problem, with either my Harley or Japanese carbureted bikes. Honestly, it is usually when I go to start it up, and feel for the petcock handle, when I realize that I forgot and left it on. I don't feel too bad about it - happens once in awhile. I always leave it to "on", for brief stops. I don't need to ride any bike I can't trust to sit for a few minutes or even hours, without leaking gas. But yeah, I should remember to shut it off at night - I am getting more forgetful, too!
I have had more of a problem, fiddling around with the dam thing when I need to switch to reserve. It's usually while underway, and I'm reaching under the tank feeling for it! That's why I try to refill at 1/2...The worst is forgetting to turn it back to "on" from reserve. I've seen problems with new riders running out of gas, because of that, so maybe its better to shut it off every time you cut the engine. At least you won't be leaving it on reserve.
Last edited by Hathaway; Aug 17, 2025 at 10:04 AM.
I've heard of it happening, and it could lead to disaster, but in 50 years and more bikes than I should have owned, many of them equipped with petcocks...never had one leak. The manual says to do it everytime you shut off the engine. Technically, that's true. I definitely shut them off if I wasn't going to ride for a couple of days, or during long spells like the winter months. But more often than not, I have left it on overnight, with no leakage. I maintain my things and my bikes were fairly modern, in good condition, so that may have helped. On an old bike with questionable carburetor, or other issues, yes, shut it everytime.
Over 2 weeks without running? Yes, I agree -shut it to "off". Every stop during a ride ? No, I wouldn't... as long as theres vacuum and valve, and diaphragm is good, it should be fine.
As is the case with any well maintained bike, they work perfectly, until they don't....
And if you rely on a vacuum petcock.......
After my leak, I started to shut it off and turn it on every time.
Got to the point where I did it automatically, like pulling the bike up level and stowing the jiffy stand, and I never even thought about it...
But everybody should do what makes them comfortable...
Got to the point where I did it automatically, like pulling the bike up level and stowing the jiffy stand, and I never even thought .
This is actually the key, to just do it every single time, its automatic, and you can worry about something else.
We dont know what happens next, might not get back out to check on the bike because of life happening. These petcocks where on the earliest of motorcycles for reason.
Switched to a mechanical Pingel Power-Flo the other day didnt even think to switch it off.
came home from work the following day to this:
luckily, it didnt fill the case, just had a bad float seat and about half a tank went out the overflow.
took the carb off, cleaned it up, set the float to the proper height (because it was WAY off) and now she runs better than ever and no leaks!
still getting used to flipping the petcock though, really need that muscle memory to set in because I went to ride today and made it about 200ft from my driveway before it just died causing me to go Oh right *flip* lol
Might be referring to a Norton Commando, that is how they shifted prior to 1975 and on the right at that...I have one and adjust OK when I ride it. It even has a mechanical gear indicator ;-).
So far as the HD petcock goes (on my Dyna) I don't bother with it for a relatively short stop because I know that the vacuum shutoff works OK since I've had the tank off a few times recently...but I do shut it off overnight at home.
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