Pet cocks ... should gas leak when left "on?"

[LCS249]

The guy who sold me the bike said I had to leave the pet cocks "off" when the bike wasn't running or gas would leak.

He was right.

On my Triumph (and I thought on my former Yamahas) it doesn't matter much.

So, is it normal for gas to drip out if they're left "on?"

thanks, Leon

[TopCatGr58]

Hey Leon,

The Special/MNS petcocks are gravity feed. The fuel is routed through a vacuum control valve system called the OCTOPUS!

SO...when the petcocks are "ON", they will flow fuel, but should be stopped by the Octopus IF you still have one. Then the fuel should also be stopped by the needle float valves to prevent flooding/overflowing the carbs.

IF you have removed the OCTY, then it's wise to turn the petcocks to OFF, to prevent possible leakage to the carbs, and then possible leakage at the carbs which could flow into the throat of the carbs, into the engine head, and down into the cylinders, past the piston rings and into the engine oil, contaminating it, causing the engine to loose lubrication and burning/spinning bearings, seizing engine, etc.!
T.C.

BTW, info like this is in the tech tips, not trying to deter you from posting, but just recommending more browsing!

[LCS249]

Hey T.C.,

Thanks for that very thorough reply.

I only just got the bike and have done nothing to it.

If the OCTY was removed, is it recommended that it's replaced?

Sounds like it from your very scary consequences description.

This could also explain the excessive fumes when starting up the bike...

I'll keep searching through tips and archives.

thanks, Leon

[oldnortonrider]

In my opinion, they'll always leak~~some. With or without the octopus. Don't worry about the fumes; that's just the breather clearing it's lungs. Octopus is alright if you understand what it does. Standards have the "octopus" (vacuum piston diaphragm off/on) built into the petcocks. Did the PO also explain to start on "Prime"?

Even with inline shutoffs (which I wouldn't be without), they'll eventually "drip-drip" when off. And there'll be the times one forgets to turn 'em off. It takes new, or not too old, float needles and seats to be practically "fool proof". These carbs take a while
for one to learn their idiosyncrasies. Parked at an angle, on much of a lean, gas will find its way from full float bowls to intake manifold; especially if nosed a bit down hill.

[LCS249]

Thanks oldnortonrider,

Helpful additional info.

The "PO" (prior owner?) said he never used Prime. Just switch to "ON."

That made me a little leery. Sounds like fuel flows a little too freely.

On the Triumph -- another carburetor bike -- you have to use "PRI" if the bike hasn't been ridden for more than a week.

So carburetors aren't new to me, but the leaking is.

The Triumph is always in the "ON" position, except when it has to be turned to "RES..." oh-oh ...

Hey, speaking of fuel, how do you actually fill up at those stations with auto-shutoff pump handles?

I've tried a bunch of things, including pulling the rubber hood back with my hand.

what works?

best, Leon

[Crazcnuk]

I would ask what you mean by 'leak'?

They should never leak, or drip externally.

If you have a standard, then the petcocks should not leak (flow fuel when the bike is not running). If they do they nead to be repaired, kits are available.

My tank sat all winter on the shed floor and didn't leak at all, out of either side.

What they are saying about the octopus, is that the vacuum valve is on the engine, not the petcocks on the specials. THose petcocks will flow fuel at all times, unless they are turned to off.

If you don't have the octopus, then you have to to turn them to off when parking the bike.

As for turning to prime, you should never have to prime the carbs, except if they bowls have been emptied or the bike has sat for a few weeks or more.

I was having to turn mine to prime to start it, but once I got the carbs set and synched I don't have to do that anymore.

[LCS249]

Hey Crazcnuk,

Gas drips when the petcocks are left in the "ON" position, which I have done a couple of times now ...

So you're saying OCTY (OCTOPUS) or not, I have to turn them to "OFF" in order to not have any drips / leaks.

When I do (after smelling the gasoline) they don't drip any more.

best, Leon

[Crazcnuk]

Well, if you unplug the hose, in any position other than off, gas should pour out like there is no tomorrow, depending on how much gas is in the tank. If the gas is low enough in the tank, it won't come out in the 'on' position, but would still pour out in Prime or Res positions.

When you say leaking what do you mean? dripping on the engine, running out the carbs, what?

If you put the petcock in the 'off' position and pull the fuel line at the petcock, it should not drip. If it does you need to rebuild the petcock(s).

In any other position gas should come out freely (as long as there is sufficient fuel in the tank).

If one fuel line from each petcock goes from the petcock to a valve near #2 carb, with 4 other hoses coming out of it, you still have the Octy. That valve is the safety shutoff switch. It shuts off all fuel to the carbs when the engine is off.

[GtrMn]

Gas drips when the petcocks are left in the "ON" position

Where is this "drip" happening?

[LCS249]

It seems to be dripping onto the engine because it collects on the garage floor fairly soon after I turn off the bike - within 15-30 minutes. That's when I start to smell it.

I doubt I'll leave the petcocks on after stopping any more - twice did the trick.

But the questions you're all asking are what I'm interested in - where is the leak?

It'll take a little work but I plan to find out.

best, Leon

[AlanB]

Hi LCS,

If you have fuel landing on the garage floor, you need to find the source soon; I would be doing it before I rode it again!

No bike should leak fuel, no matter what is switched off, or on!

AlanB

[GtrMn]

No bike should leak fuel, no matter what is switched off, or on!

Ditto that!

Sounding like a fuel line or fuel line connection problem from what you've said so far.

[stoked]

Any plugs looking dark or any popping in the exhaust while riding? Can you pull the boots back off the carbs between the air box and carb to see if fuel is pooling there? I'm just wondering if you got a needle not seating good.

[MattWenrick]

No one mentioned that if it's only when the petcocks are on and fuel is leaking from the carb(s), that it might be a broken float post or sunken float. Isn't is a common problem?

[Crazcnuk]

That's what we are trying to determine now. Once he can locate where it's leaking from, we can be of more assistance!