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Author Topic: How a petcock is supposed to function?  (Read 10716 times)

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Offline stereosilence

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How a petcock is supposed to function?
« on: November 20, 2011, 11:51:27 AM »
I have a petcock on my bike with three positions: ON, RES, OFF. I have very little experience with these things, but it seems like you put it to ON and when it starts to sputter, you put it to RES and head to a gas station. The PO told me when you finish riding to turn it to OFF so the carbs don't get flooded sitting there. I forgot to do this one day and when I started a bunch of gas came out of those nipples underneath the tank/seat (I assume that is why you keep it OFF).

However, not being used to having a petcock, I go out to my bike and merrily kick start it and head off down the road. A few minutes later, the bike comes sputtering to a halt and there I am kicking it like an idiot until I realize the petcock is OFF. I have done this twice so far.

I don't understand how the bike can run with the fuel off. Is it just the gas left in the lines or what?
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Offline TommyT

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Re: How a petcock is supposed to function?
« Reply #1 on: November 20, 2011, 11:58:26 AM »
It will run for a bit with the fuel in the bowls and the lines.  I'm sure everyone has done that before.  I put a little sticker note on ignition switch that says fuel so it reminds me to check it.
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Offline Stev-o

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Re: How a petcock is supposed to function?
« Reply #2 on: November 20, 2011, 12:29:36 PM »
First off welcome!

I believe you understand the operation now.  One other item to help you understand: the fuel system is gravity fed, there is no fuel pump.
Get in the habit of turning on the fuel whenever you turn on the ignition and off for both as well.
I just have a mental checklist for a cold start:
1. Choke on
2. Fuel on
3. Ignition on and start.

Now how 'bout posting some pics of your bike?
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Offline Terry in Australia

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Re: How a petcock is supposed to function?
« Reply #3 on: November 20, 2011, 12:37:54 PM »
In Oz, we've always called it a Fuel Tap. "Pet Cock" always makes me giggle........ ;D
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Offline Rigid

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Re: How a petcock is supposed to function?
« Reply #4 on: November 20, 2011, 12:43:57 PM »
Airplanes will do the same thing.  I suspect there is just enough fuel in the lines and bowl to get you off the ground, with too little runway left to land.  It is a conspiracy!
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Offline Stev-o

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Re: How a petcock is supposed to function?
« Reply #5 on: November 20, 2011, 01:25:46 PM »
Quote from: Terry in Australia on November 20, 2011, 12:37:54 PM
In Oz, we've always called it a Fuel Tap. "Pet Cock" always makes me giggle........ ;D

That's the real question: who and why named it a pet cock?!?

And have you heard of a stopcock?? 
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Offline CycleRanger

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Re: How a petcock is supposed to function?
« Reply #6 on: November 20, 2011, 01:58:33 PM »
Quote from: Stev-o on November 20, 2011, 01:25:46 PM
Quote from: Terry in Australia on November 20, 2011, 12:37:54 PM
In Oz, we've always called it a Fuel Tap. "Pet Cock" always makes me giggle........ ;D

That's the real question: who and why named it a pet cock?!?

And have you heard of a stopcock??

The internets say:

""Petcock" is actually a relatively new word, first appearing in the mid-19th century, but several aspects of its derivation are somewhat mysterious. The "pet" part seems to be rooted in an old sense of "pet" meaning "small," possibly related to our modern "petty," in turn harking back to the French "petit" (small), which all makes sense since a "petcock" is, as we noted, a small faucet. The "cock" part is more problematic. My own sense is that it is probably rooted in the verb "to cock," meaning "to turn up" (as in "cocking one's hat") or "to block," drawn from the defiant behavior of roosters. Whatever the logic of the term, "cock" has been used to mean "spout or faucet" since the 15th century, and is also found in the word "stopcock," which also means a small adjustable faucet."
http://www.word-detective.com/032602.html

As far as the operation of petcock on the tank, the operation is explained in the owners manual.
A pdf of which can be downloaded here: http://www.honda4fun.com/libretti/libretti.html
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Offline CrankyOldGuy

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Re: How a petcock is supposed to function?
« Reply #7 on: November 20, 2011, 02:06:51 PM »
Terry,

It must be a British carryover ... I tend to call it a fuel tap myself.   Petty ... meaning small ... made me laugh  ;D

Harry O.
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Offline BeSeeingYou

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Re: How a petcock is supposed to function?
« Reply #8 on: November 20, 2011, 02:26:29 PM »
Quote from: Terry in Australia on November 20, 2011, 12:37:54 PM
In Oz, we've always called it a Fuel Tap. "Pet Cock" always makes me giggle........ ;D

Me too.  Imagine if your wife had a bike.....I am having problems with my wife's petcock..... ;D

It is good practice to shut it off when the bike is not running.  It's really a safety issue.  If everything is in good working order, your needle valves and float setting, it should not leak even if left on.....but incorrect float setting or a leaking needle valve will cause the carb to leak.  Maybe you should check these two things.
« Last Edit: November 20, 2011, 02:29:37 PM by srust58 »
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Offline Terry in Australia

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Re: How a petcock is supposed to function?
« Reply #9 on: November 20, 2011, 02:46:58 PM »
Hmmnnnn, so if "Pet" means small, maybe I do have a "Petcock" after all................  ::)
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I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline Retro Rocket

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Re: How a petcock is supposed to function?
« Reply #10 on: November 20, 2011, 03:31:40 PM »
So, does a pet cock live in a cock pit...?   ;D ;D
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Offline TommyT

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Re: How a petcock is supposed to function?
« Reply #11 on: November 20, 2011, 03:38:59 PM »
Questions for you guys.  My bike seems to run good when I have a half tank or more.  Once I get down below half tank it cuts out at anything above 5K and if on reserve it won't really rev past 3K.  Fill it back up and problem goes away. 

The flow from on to res is dramatically different.  RES is a slow dribble and on is a steady stream.

I check the rubber gasket and it has the half circle opening but could that be my problem where it's just not filling the bowls as fast as the engine is using the fueL??
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Offline CrankyOldGuy

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Re: How a petcock is supposed to function?
« Reply #12 on: November 20, 2011, 03:47:09 PM »
Terry,

You said what I wanted to  :o

Harry
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Offline Terry in Australia

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Re: How a petcock is supposed to function?
« Reply #13 on: November 20, 2011, 04:08:39 PM »
Quote from: CrankyOldGuy on November 20, 2011, 03:47:09 PM
Terry,

You said what I wanted to  :o

Harry

:D ;D
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I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)

Offline Doggie

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Re: How a petcock is supposed to function?
« Reply #14 on: November 20, 2011, 04:48:51 PM »
I drove the lady at work crazy when I said I just won a bid for a "petcock". She said" You can get one and I can't"....
                                 Doug
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Offline anotherCB

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Re: How a petcock is supposed to function?
« Reply #15 on: November 20, 2011, 05:40:43 PM »
I always leave mine "on" never had any issues/leaks.
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Offline Stev-o

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Re: How a petcock is supposed to function?
« Reply #16 on: November 20, 2011, 05:42:27 PM »
Tommy - I think it's time to clean your pet cock!
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Offline Grabcon

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Re: How a petcock is supposed to function?
« Reply #17 on: November 20, 2011, 06:50:58 PM »
I have had issues with the petcock getting dirty and then the bike feels like it is starved for fuel.

First I would remove the petcock bowl with the petcock in the off position. Clean the bowl and remove the little flat filter screen and o ring trying not to damage either. Clean the screen.

Before reassembly get a small widemouth container and put it under your petcock and turn it on and see what type of fuel flow you get in the on and reserve positions. flow should be the same for both, if the fuel is above a 1/2 tank.

If fuel does not flow freely remove and empty tank, take petcock off and clean. Check tank for sediment. clean if necessary. reassembly and check the flow on the way to make sure everything works.
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Offline Tews19

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Re: How a petcock is supposed to function?
« Reply #18 on: November 20, 2011, 07:05:40 PM »
Quote from: Terry in Australia on November 20, 2011, 12:37:54 PM
In Oz, we've always called it a Fuel Tap. "Pet Cock" always makes me giggle........ ;D

Hilarious!!! My friends always say WTF when I say Pet Cock.... Of course they do not know bikes.
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Online bryanj

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Re: How a petcock is supposed to function?
« Reply #19 on: November 20, 2011, 11:17:57 PM »
OK enough on petcocks, what aboout gudgeon pins!!
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Offline TwoTired

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Re: How a petcock is supposed to function?
« Reply #20 on: November 21, 2011, 12:20:23 AM »
Quote from: TommyT on November 20, 2011, 03:38:59 PM
Questions for you guys.  My bike seems to run good when I have a half tank or more.  Once I get down below half tank it cuts out at anything above 5K and if on reserve it won't really rev past 3K.  Fill it back up and problem goes away. 

The flow from on to res is dramatically different.  RES is a slow dribble and on is a steady stream.

The flow issue is related to head pressure.  Head pressure is caused by the weight of the column of fuel above the drain point.  The pressure reduces as the column gets shorter.

Another issue can be long loops of fuel line where fuel is forced to fight gravity, and places where air can get trapped with no means of escape.  Air weighs less than fuel so it reduces head pressure when fuel is replaced with air.

However, I'm not yet convinced your 3k rpm issue is solely a tank fill level issue.  I'd want to carefully check the actual fuel level in the carb bowls.

Then there are the carb jetting issues which comes along with air inlet and exhaust changes, and has very little to do with fuel valve.


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Offline Rigid

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Re: How a petcock is supposed to function?
« Reply #21 on: November 21, 2011, 03:41:00 AM »
Quote from: TommyT on November 20, 2011, 03:38:59 PM
Questions for you guys.  My bike seems to run good when I have a half tank or more.  Once I get down below half tank it cuts out at anything above 5K and if on reserve it won't really rev past 3K.  Fill it back up and problem goes away. 

The flow from on to res is dramatically different.  RES is a slow dribble and on is a steady stream.

I check the rubber gasket and it has the half circle opening but could that be my problem where it's just not filling the bowls as fast as the engine is using the fueL??

Reserve draws from further down inside the tank, at the bottom actually.  I suspect you have a slug of sediment (rust) covering the inlet hole for the reserve.  The finger screen inside the tank would negate this possibility but my guess is it is gone, or compromised.  I have seen them so bad inside that the screen was gone, the standpipe was rusted off and rattling around, and the reserve hole was plugged completely shut.  All on a running bike. 
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Offline BeSeeingYou

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Re: How a petcock is supposed to function?
« Reply #22 on: November 21, 2011, 01:44:04 PM »
Quote from: bryanj on November 20, 2011, 11:17:57 PM
OK enough on petcocks, what aboout gudgeon pins!!

Don't forget about the pintles. :)
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Offline Rigid

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Re: How a petcock is supposed to function?
« Reply #23 on: November 21, 2011, 01:47:00 PM »
So my petcock flow is directly related to the amount of head?  I am starting to see some parallels with my two favorite things to do with my spare time.
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Offline Rgconner

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Re: How a petcock is supposed to function?
« Reply #24 on: November 21, 2011, 02:27:53 PM »
I know that my petcock lever markings was very... confusing.

The back of the lever where it connects looks a lot like half an arrowhead and the other end is kinda "V" notched like the feathers of an arrow, and the instructions say: point the arrow towards "ON" or "Reserve"

The actual arrow, stamped on the lever, pointed the opposite way, to the "feather" end of the lever and it was too worn to be seen easily.

Thankfully, I rolled into a gas station right as I ran out of gas!

I always feel like I am starting an X-Wing fighter when I start it up: Clutch Neutral? check. Fuel on? Check. Choke on? Check. Ignition switch to run? Check. Key on? Check. R2 Unit secure? Check.

Ready for primary ignition... Roger.


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