why a petcock


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RBGERSON
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why a petcock

Postby RBGERSON » Fri Feb 19, 2016 5:05 pm



Sevral issues on other threads about fuel , petcocks, etc. Most say to bypass the petcock as one of the ways to eliminate or ID issues..so why eliminate the petcock permanently?? One less thing to fail...or does it really served some purpose...like slowing/metering fuel??


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Re: why a petcock

Postby harvey01 » Fri Feb 19, 2016 5:15 pm

I would not eliminate the peacock. Honda put it there for the rider to be able to cut the fuel off to prevent it overflowing into the carbs and even draining into the pistons causing a condition known as hydrolock. This causes rods to be bent!

Yes you can disable this but I would not. Eventually Honda found a better way. Leaving it intact also makes it easier to remove the tank as well as prepare for winterization.
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Re: why a petcock

Postby virgilmobile » Fri Feb 19, 2016 9:08 pm

When I got my bike,the petcock valve leaked fuel...At that time,I couldn't source one or a kit.
I removed it and installed a manual lever valve.I do have to remember to turn it off at night.. (and then back on. :mrgreen: ) just like my other wings.
There is another option too.A bit of recearch will lead you to a electric fuel valve that is a sutable replacement.
Just for simplicity and reliability,I left the manual lever type.
Shutting off the fuel is important...bikes,even all of mine,when the fuel is left "on" have a chance of leaking fuel and hydrolocking the engine.
It has happened on every wing I've owned..At least once..Forgot to turn off the gas every time.The "auto valve" is just a handy thing to have .Just one less thing to remember to do.

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Re: why a petcock

Postby ct1500 » Fri Feb 19, 2016 9:39 pm

With any stored gasoline source above a carburetor there is always a chance of leakage which can cause mechanical/property/fuel ignition problems.

In particular a MC which can tip-over unattended allowing floats to open the float valves spilling entire contents of a tank of fuel, not a good scenario hence a petcock and an automatic one to boot. :D
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RBGERSON
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Re: why a petcock

Postby RBGERSON » Sat Feb 20, 2016 7:57 am

OK i get the fuel into cylinder issues and have it seen it plenty of times on 1000' and 1100's where a full tank provides fuel above the filter, pump and carbs..but on a 1500 the fuel line from the tank runs "up hill" to the filter and petcock not to mention getting the fuel out of the tank is straight up w/o a pump I don't see how it could get up and out unless there is a vacuum/suction thing going which from the carbs or cylinders on how can the fuel just leak or "run" into the carbs.

What am I missing???
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Re: why a petcock

Postby ct1500 » Sat Feb 20, 2016 8:59 am

RBGERSON wrote:OK What am I missing???


It is a safety feature which is almost invisible and totally automatic which will last 15-20 or more years before needing a $20 part replaced. :?
Last edited by ct1500 on Sat Feb 20, 2016 9:30 am, edited 2 times in total.
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Re: why a petcock

Postby dingdong » Sat Feb 20, 2016 9:15 am

RBGERSON wrote:OK i get the fuel into cylinder issues and have it seen it plenty of times on 1000' and 1100's where a full tank provides fuel above the filter, pump and carbs..but on a 1500 the fuel line from the tank runs "up hill" to the filter and petcock not to mention getting the fuel out of the tank is straight up w/o a pump I don't see how it could get up and out unless there is a vacuum/suction thing going which from the carbs or cylinders on how can the fuel just leak or "run" into the carbs.

What am I missing???



Hmmm? Good question. I never thought about that. Will wait for the experts to answer while I go into contemplation mode. :?
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Re: why a petcock

Postby virgilmobile » Sat Feb 20, 2016 9:44 am

A rare set of events...
A full tank...A few mile home...Tank gets a pressure buildup from heat.. (loosen the cap and hear it release the pressure)...Valve bad leaking fuel past it.. (remember the pressure in the tank?).....bike has one carb that didn't seal the fuel (just like the 1100 did)...

How do I know this....For testing my 88,I removed a bad petcock and once parked the bike on the side stand for a couple of days..I did not relieve the tank pressure....I hydrolocked the engine...one cylinder on the left side...

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Re: why a petcock

Postby themainviking » Sat Feb 20, 2016 9:52 am

seems to me that the siphon effect could still drain the fuel down to the level of the fuel pickup in the tank, if conditions were right. The carbs are still below the level of the fuel intake. I dunno, but just to be safe, I have always wanted a petcock on my bikes. I have had them drain a tank of fuel out onto the floor of the garage when the float in the carb cracked. Also ruined a perfectly good oil change by filling it up with gasoline. Now, this has not happened in many years, but I think "If something CAN go wrong, then it WILL go wrong eventually".
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Re: why a petcock

Postby FM-USA » Sat Feb 20, 2016 10:10 am

And how about fuel expansion?
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Re: why a petcock

Postby RBGERSON » Sat Feb 20, 2016 5:10 pm

NOW heat pressurizing the tank/gas and pushing to fuel up an out I see as possible..but you'd need a nearly full tank and lots of heat..don't the 1500 gas gaps have vents like the 1100's ??? to avoid pressurizing the tank???if not they should. Anyway if one put a valve in the line (on/off) all the issues would be solved and one could eliminate the issues with the automatic petcock... leaky diaphragms,lack of vacuum due to cracked tubes, etc. two additional hose clamps..all minor stuff until one fails!! and leaves you stranded in the dark, on a country road miles from anything with out a flashlight.. :lol: I guess carrying a piece of tubing cut(a copper tube might be best) to lenght and bent to fit between the two line ends cutting out the petcock would also fix the problem...worth making and carrying I guess..and the tools to install it.
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Re: why a petcock

Postby Bluewaterhooker0 » Sat Feb 20, 2016 9:29 pm

Somewhere on here, I read a rather extensive description of the workings of the 1500 fuel cap. Not as simple as it would appear. It has valves and 'springs' that establish and maintain certain levels of pressure in the gas tank, and also work to prevent a vacuum from forming. As I recall, the tank is still under pressure when the cap is working properly. Low pressure, but enough to push fuel through the line of an unseated float needle. I have also read that when the tank is full, gravity does, indeed, come into play, as the fuel level is above the hose levels. Because of that, it has been suggested that a full tank will allow you to run the bike with a non-functioning fuel pump, until the level again drops below the hoses.

Found it:

viewtopic.php?f=19&t=30077

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Re: why a petcock

Postby Charlie1Horse » Sat Feb 20, 2016 11:25 pm

So. . . What's the point?? You can rebuild the vacuum controlled fuel shutoff valve for $21.00 and it will probably last longer than you will own this machine. Or you can spend the same amount for a manual fuel shutoff valve which you would probably forget to turn off occasionally which would defeat the whole purpose of the change. Or you could bypass the shutoff altogether which could still siphon over to the carbs anyway, depending on heat, pressure, and fuel level. Once the fuel lines are full of fuel the fuel can still siphon over the uppermost level of the fuel line until the fuel level in the tank drops to the lowermost level of the carbs. For me, the options are only one, order the $21.00 kit and rebuild the factory fuel shutoff valve. Done and Done. No Worries, works like a champ. Really easy to do, too.
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Re: why a petcock

Postby FM-USA » Sun Feb 21, 2016 12:47 am

I know that $21.00 sounds like a great deal considering OEM's price.
My petcock rebuilding cost me about $0.015 plus my time.
Don't call it cheap, call it realistically frugal. 8-)

BTW:
I had to take a regander at my petcock and fuel filter today. I noticed they are both above the tank.
*IF* I fill the tank to the absolute top of the filler neck, only then will fuel be higher than the petcock and fuel filter... but not by much more than an ounce or two.

The point about the petcocks being unnecessary extra parts thus creating possible extra places for leaks.
Use that same analogy for engine gaskets. :roll:

.
"OIL CHANGE?" _FM 07-2009
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Re: why a petcock

Postby Charlie1Horse » Sun Feb 21, 2016 2:13 pm

Study up on how siphoning works and you will see the flaw in your logic. It doesn't have anything to do with how high the siphoning line is routed. Once the line is filled the down side of the fuel is heavy enough to keep it siphoning until air enters the intake end of the line. If you are siphoning from one can to another you can raise the center of the line as high as you can and it will still siphon from the higher one to the lower one until the levels are equal or else air enters the intake end of the line.
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Re: why a petcock

Postby RBGERSON » Sun Feb 21, 2016 3:03 pm

Just an FYI I have already changed the diaphragm in my bike's petcock. I Understand the need for a petcock where the gas source (tank) is above the carbs/pump/filter etc. Just looking at the layout of the 1500's tank, pump tubing,filter, carbs it's all uphill to the carbs..so it would take a very full tank and lots of gas expansion/pressure to push gas up to the top of the tank, up the lines, through the filter to the carbs..so not very likely unless the bike was laid down. So it seems the petcock on 1500's while adding several points for failure only protects from a very unlikely situation where gas could be siphoned into the carbs from a tank that is lower/down hill from the filter and carbs and the exit point is on top of the tank.

A permanent by pass doesn't seem like it has much downside especially if one put a manual shutoff in the line maybe even a check valve/one way pressure valve that would only open with X?? pounds or so of pressure whatever would be essay for the pump to overcome and eliminates two major points of failure the diaphragm and the vacuum line.
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Re: why a petcock

Postby FM-USA » Sun Feb 21, 2016 7:10 pm

What I see here there are 3 right ways of doing this.
The OEM way, no way (removal) and whatever way you do it.
In all basics ¯\_(ツ)_/¯ ... IT JUST DOESN'T MATTER until the bike is sold.
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Know its new taste and be loyal, you'll know when to change that oil.
Taste testing as the miles flow, souring as that acid grows.
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Re: why a petcock

Postby Bluewaterhooker0 » Sun Feb 21, 2016 7:42 pm

RBGERSON wrote:Just an FYI I have already changed the diaphragm in my bike's petcock. I Understand the need for a petcock where the gas source (tank) is above the carbs/pump/filter etc. Just looking at the layout of the 1500's tank, pump tubing,filter, carbs it's all uphill to the carbs..so it would take a very full tank and lots of gas expansion/pressure to push gas up to the top of the tank, up the lines, through the filter to the carbs..so not very likely unless the bike was laid down. So it seems the petcock on 1500's while adding several points for failure only protects from a very unlikely situation where gas could be siphoned into the carbs from a tank that is lower/down hill from the filter and carbs and the exit point is on top of the tank.

A permanent by pass doesn't seem like it has much downside especially if one put a manual shutoff in the line maybe even a check valve/one way pressure valve that would only open with X?? pounds or so of pressure whatever would be essay for the pump to overcome and eliminates two major points of failure the diaphragm and the vacuum line.


I don't have a dog in this fight, and no real concern about which way the issue is addressed, but wanted to clarify a point of your thinking. The amount of pressure generated by the gas tank, at any given temperature, which (temperature) is what will be responsible for the pressure, doesn't have much to do with the quantity of gasoline in the tank. Gas, or any liquid, can turn into a vapor, and then create pressure. A closed, sealed tank, with a 5 gallon capacity, holding 1/2 gallon of fuel, will produce exactly the same pressure as the same tank holding 4.9 gallons of fuel at 100F. It is for that reason that rockets, or even steam locomotives were possible so many years ago. The expansion of the fuel, or water in the case of steam engines, is how they were able to carry enough fuel or steam to make either device practical. The liquid can produce many times the quantity of vapor when it changes state. So, the quantity of gas in your tank will not effect the pressure generated by the tank, until the liquid is gone, and only vapor remains. In the air conditioning business, Freon, or refrigerants, behave exactly the same, only at much lower temperatures, or boiling points. Pressure is a constant, as long as liquid remains.

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Re: why a petcock

Postby RBGERSON » Mon Feb 22, 2016 7:35 am

I get that but with a full tank the liquid is already closer to the outlet and you'd need less vapor to start it up the the fuel lines..with less full tank..gas further from the top and it would require more vapor to form before pressure started to effect the liquid and it would have to have more pressure to raise the liquid as it would have further to go. Just sayin' it it very unlikely given the full system layout on the 1500's.

No fight, just a civil discussion for discussion's sake..bouncing around thoughts..
Last edited by RBGERSON on Mon Feb 22, 2016 11:06 am, edited 1 time in total.
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Re: why a petcock

Postby FM-USA » Mon Feb 22, 2016 7:49 am

I learned a very long time ago one can "Pick Apart" anything someone else did.

Why would Honda bother with the overall expense if there wasn't good reason for that petcock being there?
Apparently your safety was paramount along with saving your bike from probable harm by fire on a simple tip over.
As you point out a manual shut off will be forgotten now and then so the probable risk is now higher of an incident than the OEM way.

Not bark'n at ya (that's Hillary's job), just continuing the reasons for/against the removal of the petcock.

.
"OIL CHANGE?" _FM 07-2009
Know its new taste and be loyal, you'll know when to change that oil.
Taste testing as the miles flow, souring as that acid grows.
And don't flirt with dirt or darkened oil, all the faster your engine will spoil.

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Re: why a petcock

Postby RBGERSON » Mon Feb 22, 2016 11:08 am

What about the idea of a simple one way check valve..that requires some pressure to open but more than a vapor expansion could muster, pressure wise???
HAD LOTS OF GOLDWING 75-83
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Re: why a petcock

Postby FM-USA » Mon Feb 22, 2016 11:34 am

What I understand from what you wrote here is all you want to do is remove possible fuel leaks.
Adding anything to the fuel line from tank to carbs is adding more than 2 clamps.

Did you have an incident in the past that begets you to want to change the safety portion of fuel systems?
Otherwise, as for me, I don't understand the wanton change except to just change.

Personally I would love to change to a direct line to get me more storage for 'in reach while riding' items.
But I have my special someone with most times and don't want to risk her safety.
.
"OIL CHANGE?" _FM 07-2009
Know its new taste and be loyal, you'll know when to change that oil.
Taste testing as the miles flow, souring as that acid grows.
And don't flirt with dirt or darkened oil, all the faster your engine will spoil.

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Re: why a petcock

Postby ct1500 » Mon Feb 22, 2016 7:02 pm

If you and the bike ever go down with it pinning you or even on top of you the last thing you want happening is a tank of gas flowing out on you or hot engine parts.

The BAS kills the ignition and fuel pump and the automatic petcock stops any further flow.
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Re: why a petcock

Postby flogger » Mon Feb 22, 2016 7:44 pm

Ok, I will put this in the simplest layman's terms... however I welcome experts and engineers to chime in and I am sure some will even put it more academically "truthful" or more correct info... But I am merely relying on my old-timers experience as a long time rider...

As an old-timer, we were always taught years ago to shut off our fuel (petcocks) each time we shut down our cycles and parked them. I believe all or most cycles always had petcocks and that all or most probably all- always had a gravity feed petcock.

Why do we have a petcock?

I think this was first for performing maintenance and removing/repainting/replacing gas tanks... then secondly the petcock was for keeping the operator from inadvertently running themselves out of gas as a benefit offered from manufacturers to consumers. Lastly the petcock evolved into the vacuum petcock we know today stemming from a Federal government mandate in the late 70s or early 80s. This was to aid first responders when at accidents so that the gas was shut off automatically if the cycle was down...

Simple logic for it's being there and yes, you could remove it easily and do without it but probably not too wise... I have seen folks remove the vacuum and convert them back to gravity feed on many models of cycles preferring that as to fixing vacuum or fuel issues. There is no problem with that but you must act as the old school riders then and always shut off your petcock...

This post is generic and is not Wing nor any model of cycle specific... And most all bikes evolved from models and years where the petcock was below the tank and above the carbs...


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