"Scooter Valve" vacuum line modification

[Wilder]

Installing a Dan-Marc electric fuel solenoid into the fuel line is a popular approach to avoiding having a hydrolock event damage our Valkyrie engines.  But this still leaves us vulnerable to gas flowing down the vacuum line from the petcock to intake #6.  This modification to the vacuum line is similar to the modification we make to our fuel lines, in that it puts an automatic check valve inline to allow passage inside the line only when the engine is on.  I will explain the exact steps and parts needed below.

First, I want to acknowledge that if anyone has fuel getting into their cylinders, there is something that needs to be addressed in addition to installing either a Dan-Marc or a Scooter Valve.  There is either a leaking diaphragm (or both of them) in the OEM petcock causing fuel to flow down the vacuum hose, or there is a leaking float valve in one of the carbs.  These faults must be addressed.  A Dan-Marc and a Scooter Valve are both nothing more than devices designed to prevent a catastrophic failure in the event of a gas leak.  These are not our first lines of defense, but rather back-up or "fail safe" devices.  So, if there is a problem, fix it as soon as possible.

The Scooter Valve modification has to do with only the vacuum line going to the petcock.  It effectively plugs off that line from anything (air or gas) going either direction when the engine is not running.  Some people prefer to switch ot a manual petcock such as a Pingel one, and others prefer to switch to a different vacuum-operated petcock.  My view is that the OEM petcock is a good device as long as the diaphragms are in good shape; and that rebuilding the OEM petcock at least every 10 years with a new Honda "cover set" is a smart idea.  In order for a hydrolock to take place, fuel must be flowing through that petcock in one direction or the other - or potentially both.  Those rubber diaphragms can't last forever, and there are many still in service that are 20 years old.  They will fail, sooner or later.

My older son rides a Yamaha V-Max and discovered that speeding on the highway at twice the posted speed limit in NC will cause you to lose your license on the spot for a year, and be given a ride to jail in the back of a Highway Patrol car.  He then bought a Kymco brand 50cc Moped for transportation to and from work.  I was working on his moped and discovered this neat little vacuum-operated fuel shutoff inline in the moped's fuel line.  This was over 3 years ago, and I immediately ordered one of those valves and fashioned my first "Scooter Valve" modification for my Valkyrie.  I have since refined the concept and have installed them in 5 additional Valkyries.  So far, these 6 "Scooter Valves" are 100% operational.  Periodically I re-test my own, and it passes with flying colors.  Yesterday I ordered supplies to make 10 Scooter Valves to take with me to Inzane.  I will sell them for $25 installed, $25 mailed within the US, or $20 in person with no installation.  These things are neither expensive or complicated, and installation takes under 5 minutes total once they are made.

Here's what you need:
1.  A vacuum-operated 50cc scooter/moped fuel cutoff valve.  They are available on ebay for all sorts of price points.  You can find one made in China for $6 with free shipping from a US seller.  I prefer one that costs $8.50 each and is made in Taiwan.  I think it is better quality, but they do the same thing.  When you hold them in your hand to compare side-by side, they are essentially the same but the casting of the body is smoother with the Taiwan model.  I assume it is smoother inside as well.  It's just worth it to me to spend a couple of more bucks and have something that I am confident will last a long time.  This is also why my son bought a Kymco instead of the Chinese scooters that are available.  The quality is better.  It's worth a few more dollars.  Enough of that rant. On ebay, search for Vacuum Operated Mini 3-Way Fuel Valve Petcock.  Get the 3-Way, not the 4-Way.  Take your pick, there are several choices.
2.  You need some small (5mm / 3/16") vacuum tube.  I use silicone tube because it is far more heat resistant and long lasting.  If you have done a desmog and have the parts on a shelf, you have some already.  It only takes a few inches.
3.  You need a plastic "Y" fitting designed to split a windshield washer pressure line into 2 lines, so that the spray will shoot out of 2 nozzles.  It's easy to find at an auto parts supplier, but apparently the volume of these being sold is low because they are about $2.50 each.  That's a lot for what they are but I have not found anything better.  The problem with these is that they are white, or at least all I have found are white.  That can show up in a place where we might prefer it to disappear.  My solution is to use a black sharpie marker and color the center inch of the Y black.  The "legs" of the inch are going to be inside black hoses, so no need to color them.
4.  You need 6 small zip ties to use as clamps.  The connections would probably stay together anyhow, because they are pretty tight.  But I like to make sure it won't come apart, so I clamp them.
5.  You need another zip tie to secure the finished product up out of sight.  There's a convenient mounting hole on the valve itself, so I use that to secure the thing in place just because I don't want it just hanging around.  Really, it can't go anywhere.  So maybe this is not essential.  I just prefer it to be nice and tidy.

Procedure to assemble the Scooter Valve:
1.  The plastic "Y" goes on the intake manifold side of the valve.  There are 2 small hose barbs that point in the same general direction, which need to be connected to the "Y" with 2 short pieces of hose and clamped.
2.  Using a "Mighty Vac" or similar tool (or just sucking on a piece of hose), ensure that air will flow one way but not the other through the assembled Scooter Valve modification.  I actually test the valve itself before assembly with 2 Mighty Vacs, but that's not essential.  If it's working right, you will easily draw air through the end with the Y, but can't get any through the end with the single outlet to the valve.
3.  It passed the test.  You're done.

Installation: 
1.  Snip the vacuum line going to intake manifold #6 at a convenient location, making sure that you will still have enough line to work with on the end that is connected to your petcock.
2.  Inside that vacuum line there is a small, rigid plastic tube.  It is there to ensure that this vacuum line can not collapse upon itself or get kinked.  Either way, this could potentially cut off the vacuum to your petcock and result in a stoppage of fuel flow.  So you still want it, but it is now keeping you from plugging the hose into either end of the Scooter Valve assembly.  All you need to do is slide it out a little ways and cut off 3/4" of both tubes (they were one, but now they are upper and lower because you cut the hose).
3.  Connect the upper hose, going to the petcock, to the single side of the Scooter Valve.  Clamp it.
4.  Connect the plastic "Y" to the short piece of hose connected to intake #6.  Clamp it.
5.  Hide the assembly behind the left bank of carbs and zip tie it in place to something - anything will do.  You're done.

What it does:  Vacuum from the intake first opens the scooter valve and then vacuum is supplied to the petcock.  It doesn't take much vacuum to open it, but in the absence of a vacuum the valve is closed.  The scooter valve is designed for fuel to go through one side and to have a vacuum pulled on the other side.  The "Y" supplies vacuum to both sides at the same time, but vacuum is passed along to the petcock only once the valve opens.  If your petcock diaphragms have ruptured, it can pull gas down that small line, but only when the engine is running.  This will cause #6 to run rich, which it would be doing whether or not you have a scooter valve installed.  You probably wouldn't notice it unless you smell fuel odor when it's idling inside your garage - a bad sign.  But when you cut the engine off, that fuel flow will instantly stop.  This will keep intake manifold #6 from filling up with gas and hydrolocking your engine - even with a ruptured petcock diaphragm.

OK, it takes longer to describe this than it does to both assemble the Scooter Valve and install it onto your Valk.  You're going to spend around $13 (plus or minus a couple of bucks), possibly plus a small shipping charge, to make your own.  I welcome your feedback, questions, suggestions to improve it, etc. 

I hope to see a bunch of you again at Inzane.
Blessings,
Dave Wilder

[N8171S]

Just plug #6 carb, remove the diaphragm and convert the original peacock to manual.  The Dan Marc takes care of the rest.  Manual peacock still works fine to control reserve and on/off.

[Houdini]

Doesn't happen, the petcock is vented and the fuel will dump out on the block and not go down to #6.

[Wilder]

Since posting this information, I had one person on Facebook and now one here post that this addresses a problem that doesn't happen because of the weep hole in the OEM petcock cover.

The original reason for me to ponder a way to keep gas from going down the vacuum line was me encountering it on a guy's bike I fixed after it happened. I picked him and his bike up with my trailer and brought the bike to my workshop. Luckily, he had a weak battery and it didn't shear any gears. We pulled the plugs and gas spewed out of #6 only. I unplugged that vacuum hose and there was a very slow drip, maybe a drop a minute. So I know it can happen, though it seems rare.

So yesterday I spent a couple of hours on this forum, using the search function repeatedly and found several references to the petcock leaking down the vacuum line. At least 2 instances were reported to be situations where the weep hole was plugged, so when the diaphragm tore, gas went straight to #6. At least 3 were situations of the cover being "clocked" to the wrong position, leaving that weep hole above the vacuum line. I assume those instances were people having it apart and putting it back wrong, not an error from Honda. Other descriptions of this event did not suggest a cause. On the one I encountered, I replaced the cover set, but can't say for sure what position it was in, or if the hole was plugged up with junk.  It was very nasty under there, covered by the pretty chrome side covers - so it looked great from the outside.  The owner said that the tank had never been off, and the air filter attested to that being the case.  At the moment, I just replaced the parts and focused on the other issues at hand, working late one night and trying to get the guy rolling again so he could ride home and I could get some sleep.

I really do believe that the majority of hydrolock situations are from stuck floats and float valves (or those little rubber tips failing, or a speck of rust/trash, or weak springs inside the float valves, etc.). I also believe that it's possible to hydrolock with the petcock closed because of the fuel in the line. It doesn't take much liquid fuel to lock a cylinder.

The bottom line is that hydrolock is rare, but it is often catastrophic to a Valkyrie due to the design. And out of all hydrolocked engines, a small number can be traced back to the vacuum side of the petcock, for whatever reason. The percentage is unknown, but I'm sure it's low.

My scooter valve modification may not be needed but once in a rare while. And I understand why someone would think it's a waste of time and money. But I will continue using it if for no other reason than peace of mind. I also will continue using Dan-Marc number 121 because I can mount that model very close to the carbs with a brass "T" screwed directly into the outlet side - and thus limit the fuel available for a hydrolock in case of a stuck float.

I'm just throwing the idea out there for anyone who is interested.  It's a cheap and easy fix to a problem you might never encounter, but if any thing happens that causes gas to drip down that vacuum line, there will be a problem.

I've not personally tested this next theory, but I think a leak in the second diaphragm could begin slowly and the vacuum present would suck the gas straight to #6 with the engine running.  It might even suck pieces of dirt/road crud into the weep hole and cause a plug.  Just as an early test for a failing main petcock is to cut the gas off and see how far you can go before the engine starves for fuel, we should be able to check the spark plugs and see soot on #6 because of running too rich.  That leak may only be happening under a vacuum at first.  Again, this is my theory.  It is a good practice to replace the cover set periodically as a precaution, especially with ethanol in the fuel.

And another worthy approach is to do away with the vacuum line completely with either a manual petcock or a petcock conversion to manual, plus install the Dan-Marc.  Personally, I have a fresh cover set in mine (about 3 years old now), a Dan-Marc, and a Scooter Valve modification.  My float valves are about 2 years old.  I'm confident that I'm not going to have a hydrolock, but any mechanical device can fail.  Even if well maintained.

[MarkT]

Doesn't happen, the petcock is vented and the fuel will dump out on the block and not go down to #6.

This is correct.  It would take both diaphrams - vacuum and fuel control - to be holed, and the vent between them plugged for the fuel to run down #6 w/o also leaking onto the engine block and being noticed.  Also if both diaphrams are holed the engine won't run unless the holes are very small, calling attention to the problem.  This is assuming the petcock hasn't been otherwise modified.

BTW, not seen this mentioned much, but small holes such as vents are often attractive to small bugs, making nests in them.  Though in a fuel environment that may be stopped by the nasty home for them.  I had a furnace vent blower failure due to a spider making a home in a vent that controlled the vacuum diaphram switch.

I put a Dan-Marc on Deerslayer and left the OEM petcock in place.  As a preventive measure, it hadn't failed at that moment.  I had previously cleaned sand out of the petcock twice, and replaced it once, all due to failures.  George (blown bobber, below) has a Pingel and a single carb; hydrolock not possible unless I forget to shut off the Pingel - never happened yet.  Jade has a completely different fuel system with a belly tank, installed as a gravity feed, with a Pingel and a Dan-Marc.  My 4th Valk is in storage, saved as a parts bike.  I don't believe hydrolock can happen at Horseapple Ranch.

[Jruby38]

There is not enough gas in the line to cause hydro lock with a manual Pingle.  I drained  mine off and it was less than a oz.

[Bighead]

There is not enough gas in the line to cause hydro lock with a manual Pingle.  I drained  mine off and it was less than a oz.

Jruby there should be NO gas in that line. And it takes very little to hydro lock....not a chance i would take. Not saying what the OP is needed i dont think it is.....

[Gavin_Sons]

There is not enough gas in the line to cause hydro lock with a manual Pingle.  I drained  mine off and it was less than a oz.

It takes much less than an oz to lock a cylinder from making its full stroke.

[Paladin528]

The total capacity of one cylinder is 253CC about 8 oz.
Compression ration of about 9.5-1 would mean that a full hysrolock would need about 26 CC or .87 oz of fuel or more to fully hydrolock the engine.  Less than that amount will still cause issues due to the air in the cylinder as well as the fuel. 
So it takes less that 1oz to hydrolock an engine.