Petcock useful info? Function test and some workarounds for on the road fails.

[Pete]

I read all the petcock post and hydro lock post including the tech archives and realized I should post the following.

For all you folks having petcock issues with the stock petcock.

Honda did not design the fuel system to fail with a hydro lock, i.e. gas in the cylinder.

A failure of the petcock vacuum along with 1 or more float valves should overflow through
the 2 vent hoses on top of the carbs if they are not blocked or kinked.

I know that it works that way because I have seen it happen. Now that is not to say hydro lock
cannot happen it does. But with all systems working the jets resist flow more than the vent
passages.

So check those carb vents and hoses for unrestricted flow and kinks or blockages.

As for the petcock it can fail 3 ways.

Trash in the ball valve can prevent a good seal and allow gas to flow. When rebuilding
the petcock flush the ball valve chamber until it is clean and will seal in the off position.
Confirm be turning the petcock off and  blowing through the fuel hose barb.

The strainer on the petcock does let small particles thru and they can accumulate in the
ball value chamber and in the reserve orifice. Make sure they are clean.

The fuel diaphram can develop a hole allowing gas to pass into the drain chamber of the
petcock and out of the drain. Replace the diaphram to stop the gas leak. The drain hole
can become clogged by small insects make sure it is not clogged. Be careful unstopping it
without disassembly as you can easily puncture the vacuum diaphram.
 
The most failure prone part other that trash in the fuel is the vacuum diaphram. Most discover
this failure when they go on reserve early usually after at about 1/2 tank used from a full
tank. There was an earlier symptom that most miss.

Because of hole in the vacuum diaphram your number 6 cylinder has a massive vacuum
leak, is running very lean and has not been producing its share of the power. You have been
riding a 5 or 5.5 cylinder motorcycle and not noticed it.

The is a very easy test to check the condition of the vacuum diaphram. Simply attach a length
of hose to the petcock drain hole and see if it will hold vacuum. If you get air with a fuel taste
the vacuum diaphram is holed it you get gas the fuel dapharm is holed. If you get both
they are both shot (never seen that). You will normally have to hold the hose on the
drain as the nipple is very short, failure to hold it may allow air to enter and mislead you.

I have seen 2 different vacuum diaphrams in the petcocks and replacement cover sets. On one
the round protrusion in the center of the diaphram is the same on both sides on the other one side is
shorter. The short side faces the spring side and interfaces with the spring support washer.

I find it easier to remove the fuel selector assembly screw with a #1 phillips rather than a #2.
The thinner shaft of the #1 is easier to center. Remember there is a cotter key shaft offset in the
hole that causes a #2 to off center.  Also occasionally I see dirt wasp nest in the fuel selector
hole you must clean out before a screw driver will work.

For all you folks that want to do away with the diaphrams the best way is to insert some
gas proof gasket material and a slug (washer without a hole) in place of the fuel diaphram and remove the other diaphram and spring and spring seat and reassemble. Remember to then cap the vacuum port and the drain orifice. And plug the #6 carb.

If you hole a vacuum diaphram on the road stop up the petcock drain to stop the vacuum leak
and to restore fuel flow.

That is all folks, have fun and ride safe and when your 6 cylinder becomes a 5 cylinder fix the
problem rather than wait for the early reserve clue. Or if you suddenly drop a cylinder check the petcock vacuum function.

[hubcapsc]

If you hole a vacuum diaphram on the road stop up the petcock drain to stop the vacuum leak
and to restore fuel flow.

That'll cause your petcock to fill up with gas which will run down
your vacuum line to #6, filling up that cylinder with gas, causing
raw gas to shoot out your exhaust pipe and potentially cause
a hydrolock...



-Mike "I'm pretty sure... "

[Chrisj CMA]

All that.  Or just get rid of the dang thing

[Pete]

If you hole a vacuum diaphram on the road stop up the petcock drain to stop the vacuum leak
and to restore fuel flow.

That'll cause your petcock to fill up with gas which will run down
your vacuum line to #6, filling up that cylinder with gas, causing
raw gas to shoot out your exhaust pipe and potentially cause
a hydrolock...



-Mike "I'm pretty sure... "

I disagree, and have actually done it. Please rethink your comment.
If the hole is in the fuel diaphram - yes.
BUT not if the hole is on the VACUUM diaphram

There are 2 diaphrams in the petcock the drain is between the 2 diaphrams.

[Dusty]

If you hole a vacuum diaphram on the road stop up the petcock drain to stop the vacuum leak
and to restore fuel flow.

That'll cause your petcock to fill up with gas which will run down
your vacuum line to #6, filling up that cylinder with gas, causing
raw gas to shoot out your exhaust pipe and potentially cause
a hydrolock...



-Mike "I'm pretty sure... "

 Mike

Pete is right about plugging  the drain  hole to regain your vacuum . There are two diaphragms in the petcock . The drain hole is in between these two diaphragms so if the vacuum diaphragm has a hole air will get in the vacuum side  thru the drain hole. The fuel diaphragm does not have a hole in it so that diaphragm will still stop the gas from leaking out.

This would only be a short term solution to get you where you need to go.

Hope that makes sense  

Dusty

[Pete]

All that.  Or just get rid of the dang thing

Or.
Just remove the diaphrams and insert the slug and gasket in place of the fuel diaphram.
Does the same thing, makes it manual, removes the failing items and cost about $1.00.

If on the road use an appropriate size coin and a piece of rubber as a temp patch.

Your money you pick the solution.

[Pete]

In some past post on the petcock some have recommended a vacuum restriction in the vacuum line to reduce the stress on the vacuum diaphram.

That is OK until a hole develops in the vacuum diapharm, it the hole in the  vacuum diaphram is larger than the hole in the snubber, all gas flow will cease.

Removing the snubber may allow enough vacuum to restore fuel flow.

It is somewhat surprising how large the hole can  be and still allow some gas flow. The small size of the drain port seems to act as a vacuum restriction helping the holed vacuum diaphram continue to work.

[hubcapsc]

Hope that makes sense 

I think so... there's more than one part that can go bad...

If it is the diaphragm like in the picture I posted that's bad, plugging the
weep hole is definitely bad. We made a good and easy fix to the one
in the picture with a cover set. I've seen other diaphragms that had
little pin holes in them, but never saw one wrinkled up like the
one in the picture.

-Mike

[Pete]

Hope that makes sense 

I think so... there's more than one part that can go bad...

If it is the diaphragm like in the picture I posted that's bad, plugging the
weep hole is definitely bad. We made a good and easy fix to the one
in the picture with a cover set. I've seen other diaphragms that had
little pin holes in them, but never saw one wrinkled up like the
one in the picture.

-Mike

Your picture is the vacuum diaphram not the fuel diaphram as it is smaller.
If the fuel diaphram fails we agree.

If only the vacuum diaphram fails we do not agree.

Based on the position of the failure in the picture gas escaping from the fuel diaphram with the drain blocked may have caused the vacuum diaphram to fail.

Stopping the drain from functioning is always a short term get me there fix in either diaphram failure but NOT when both fail.

If you replaced only the vacuum diaphram and left the yellow cover on the drain it is going to fail again.
Hopefully you have removed the yellow cover from the drain.

If you replaced both diaphrams you should remove the yellow drain cover to restore normal function.

[John Schmidt]

To make it manual...which I'd do before a trip, remove all the guts and instead of using a slug/holeless washer, just a couple o-rings. They go where the original diaphragm set, makes it totally manual but you need to cap off the vac. and drain holes same as the other method.

[Pete]

To make it manual...which I'd do before a trip, remove all the guts and instead of using a slug/holeless washer, just a couple o-rings. They go where the original diaphragm set, makes it totally manual but you need to cap off the vac. and drain holes same as the other method.

Yes that will work also.
I like the slug and gasket approach because it does not leave gas in the drain chamber and the vacuum chamber and really does not require capping the vacuum and drain on the petcock. Capping just makes it look better. And the gasket if cut correctly is assured of alignment.

[Blackduck]

Another thing that can happen is the very fine bleed orifice in the petcock can block.
This stops vacuum from bleeding off when the engine is shutdown effectively leaving the petcock open.
Easy check is to run the engine  or apply vacuum to the line then shut off/release the vacuum. Remove the fuel line and if there is flow the petcock is staying open.
Found this out the hard way.

[Jopson]

When I converted mine to a manual petcock, I cut the center out of each of the diaphragms, effectively turning them into o'rings. So far so good, I also installed a dan Marc at the same time.

[Dusty]

Another thing that can happen is the very fine bleed orifice in the petcock can block.
This stops vacuum from bleeding off when the engine is shutdown effectively leaving the petcock open.
Easy check is to run the engine  or apply vacuum to the line then shut off/release the vacuum. Remove the fuel line and if there is flow the petcock is staying open.
Found this out the hard way.

 Another picture. I think this plugging up of the bleed hole is the main culprit for hydro lock. IMHO

Dusty   

[Pete]

On the bleed hole on the inside of the of the vacuum chamber. There is no outside hole.

On testing the vacuum side they all hold vacuum until released which seems to me to indicate no bleed.

Since the vacuum port opens to the manifold I do not see the need for a bleed hole as the manifold will assume atmosphere pressure through the idle air passage/slide idle position right after shut off.

Correction it is part of the anti back pressure system to prevent a backfire from pressurizing and blowing the vacuum diaphram.

I would leave it alone. Appears to be non serviceable. (Updated in a later post see below)

I think this needs more research, more tomorrow.

[Dusty]

On the bleed hole on the inside of the of the vacuum chamber. There is no outside hole.

On testing the vacuum side they all hold vacuum until released which seems to me to indicate no bleed.

Since the vacuum port opens to the manifold I do not see the need for a bleed hole as the manifold will assume atmosphere pressure through the idle air passage/slide idle position right after shut off.

Correction it is part of the anti back pressure system to prevent a backfire from pressurizing and blowing the vacuum diaphram.

There is a rubber flap inside the casting that you connect the vacuum hose to. The flap opens and closes on every intake  and exhaust cycle. It's job is to keep vacuum in the area behind the diaphragm  to keep it open. When you shut off the engine you lose the vacuum in the hose and the vacuum behind the diaphragm holds the rubber flap shut. . The bleed hole allows air in the hose to leak into the area behind the vacuum diaphragm and then the spring can close the fuel diaphragm over the  fuel supply port.

 In the picture you can see the flap and the bleed hole.

To prove this is how it works you can take your petcock apart and try to suck on the vacuum port on the end of the petcock. You can suck air thru the vacuum port. Now try to blow air through the vacuum port. Air will not go through.



Dusty

[/quote]

[Blackduck]

My thoughts on the check valve and bleed orifice are that they help dampen the pulse effect from using a single intake runner for vacuum supply.
The check valve holds vacuum on the diaphragm and stops the pulses from affecting the diaphragm.
The bleed orifice is small enough that there will very little pulse effect through it but will allow the vacuum to bleed off when the engine is shut off

[Dusty]

My thoughts on the check valve and bleed orifice are that they help dampen the pulse effect from using a single intake runner for vacuum supply.
The check valve holds vacuum on the diaphragm and stops the pulses from affecting the diaphragm.
The bleed orifice is small enough that there will very little pulse effect through it but will allow the vacuum to bleed off when the engine is shut off

That's exactly what the rubber one way valve and bleed orifice  do and you said it a lot better than I did.  Without the one way valve the diaphragms would be moving constantly as vacuum increased and decreased

Dusty

[Pete]

Dusty, Blackduck.
Excellent explanations, Thanks.

I am seeing some variation in the four units I have available for examination.
All four work, but 1 has more restriction on the vacuum side than the others.
All four have the same restriction when blowing into the vacuum port.

The one that is different is a 1997 unit removed at 1500 miles, so I do not suspect anything wrong.
I will look into to it this morning and post the results.   

[Pete]

On closer examination here is what I observed on the vacuum port of the petcock.
On vacuum from the engine both holes flows unrestricted.
On pressure to the vacuum port a very slight resistance is felt (could be imagination) and then air flows with the same resistance through the small hole only.

On the 1997 petcock that had somewhat restricted vacuum.
Using a light and magnifying glass I could not detect any dirt or trash in the vacuum port or the inside port. I used silicone to wash it out, still no detected dirt.
After the silicone injection the restriction on vacuum was no longer there.

I suspect that the internal rubber was stuck and the silicone injection freed it up.

So in conclusion other than back flow protection or dampening effect or bleed off, your guess is as good as mine.

I tend to think all three.

[dchester4]

So the center section has a small vent hole in it.  Does that face down?  I've seen several references telling me to put it back the same way I found it, but I'm sure which way it was.  The picture on the OEM part sites shows it facing down....

[RGM]

I just put in a new petcock in mine last week because the old one was leaking gas bad and the gas wrecked the chrome on my alt cover. The vacuum diagram was ripped so I bought a rebuild kit. Put it all together and discovered the leak was from the selector shaft. To bad no kit for that. Anyways had to buy a new petcock and after installed on tank wanted to make sure it was working properly.  I put a line on the vac port and another on the outlet to a fuel can. When I sucked on the vac line it wouldn't hold vac for more than a sec or two and from the above comments that makes sense now. Everything worked as expected and I measured the fuel reserve to be 5 liters. After putting the tank back on the bike it took my bike 9 minutes to die at idle when the fuel was shut off. I also measure how far from my driveway I could ride after turning the fuel off.  I will be testing that a few time a year to make sure it doesn't change much.

[Pete]

So the center section has a small vent hole in it.  Does that face down?  I've seen several references telling me to put it back the same way I found it, but I'm sure which way it was.  The picture on the OEM part sites shows it facing down....

Yes down so if the fuel side leaks it will leak out the hole. And down so that water cannot enter from rain and fill it.

[dchester4]

Thanks.  Down seemed right.  I'm having issues with fuel delivery when I'm at half a tank or less.  Throttle just not responsive.  Sounds like a petcock issue.  Got my coverset the other day, will be replacing shortly.

[Pete]

Thanks.  Down seemed right.  I'm having issues with fuel delivery when I'm at half a tank or less.  Throttle just not responsive.  Sounds like a petcock issue.  Got my coverset the other day, will be replacing shortly.

Yes it sure does, that is a known issue with a small leak in the vacuum side of the diaphram.

[Davemn]

All good information. Under what conditions would I not have any reserve capacity? I was able to put 5 gallons of gas in and never went to reserve. Thanks.

[Pete]

The selector was allowing fuel to pass thru the reserve when it was on no reserve.
That is usually caused by trash in the selector cavity not letting the ball seat fully to block reserve.

It is always a good move to back flush the selector cavity and ball until it is clean when rebuilding a petcock. moving the selector as you flush forward and backward will enable you to clean it well.
I use a good grade of spray can carb cleaner and then blow it out with compressed air.

If the reserve is not working properly, selector in off could also be allowing gas to flow, so be careful.

Watch those eyes, carb cleaner in the eye hurts.

[Motodad71]

Wow all these conversations and issues with the OEM petcock has got me really worried, I am about to buy a less than 7K mile 21 year old 97 in a few weeks. I test rode it today, and other than taking a bit for me to start it and ran a bit rough for about 10 minutes, once warm it ran great and started back up great. Yeah the bike had been sitting for maybe as much as 4 to 6 months, I added maybe 1.5 gallons of fresh gas and like 3 to 4 ounces of seafoam before starting it. I'll be riding it 100 miles home, and no doubt will be worried whether I'll make it home or not.  I am a total fuel injection motorcycle guy, only owned 3 previous carb bikes, and I am honestly a bit intimidated by them. No doubt a Pingel non vac will be getting installed soon, do we start the OEM petcock in the ON position or the RES position? I ask because after trying to start 3 or 4 times with full choke and in the ON position, the engine tried to start but just died, but then switched to RES and it fired right up and idled fine.

[Pete]

Normally start in the on position, unless you are low on gas. Below 1.1 to 1.3 gallon you are entering reserve so start on reserve.

I would not be paranoid about the petcock, just check it as you would any other mechanical device and repair or replace it when not working properly.

Almost any petcock can fail when contaminated with rust/scale/dirt. So watch out for rust in the tank.
The rust then contaminates the float valves. Then the combo failure of the two results in possibility of hydro lock.

Keep the tank clean and rust free is always a good idea and will reduce the potential for failure.
It is possible to have a float failure instead of rust in the float valve but that is rare. 

[Chrisj CMA]

People have different experiences, therefore varied opinions (fancy that)  In my 16 years owning and working on Valkyries I have come to the opinion that the OEM fuel valve/petcock is the only part on the bike that I would (I have done) take off and replace with a quality valve even if it's brand new and operating properly. You can sell them or trade them easier before they start not operating properly.

[Motodad71]

Roger that on the OEM unit, is there another petcock similar to Pingel which isn't Pingel price?   Nah they aren't that pricey for the quality you get, but I must admit I'm not a fan of losing half the reserve capacity.......but range is range regardless.

[Pete]

There is another way to resolve this and automate it.
Remove the petcock and replace it with a small low pressure electric pump from say a Honda V65 or others.

[Willow]

It's easier than that.

The vast majority of OEM petcocks are working fine.  If you're afraid of being one of the 2 or less percent then add an electric switch to the line.  If you really want to spend some money add an auxiliary tank below the frame.

[Locomotive]

Roger that on the OEM unit, is there another petcock similar to Pingel which isn't Pingel price?   Nah they aren't that pricey for the quality you get, but I must admit I'm not a fan of losing half the reserve capacity.......but range is range regardless.

There is a Golan which is reputed to fit and work, discussed at the following link. Probably not much if any cheaper than the Pingel but it looks like an easier design to self-service with non-proprietary parts (just o-rings) which seems like a good idea:
http://www.valkyrieforum.com/bbs/index.php/topic,43120.0.html
In some other spot I read of people having to ream the inside diameter of the tank port just a little bit to allow the Golan screen to fit into the tank.