convert frame mounted petcock for no vacuum

[ktrim]

I disassembled my frame mounted petcock and discovered the diaphragm is torn.  So, rather than runnin in prime I decided to convert it to work with out vacuum.  it was very simple and cost near nothing.   this also turns the PRI position into OFF.   all you have to do is remove the 4 screws on the rear of the petcock.  removed the spring and diaphragm (save the diaphragm).  looking at the petcock from the rear with the nipple that attaches to the carb on the right you will notice 2 holes facing you.  one in the center (tower stickin up) and one directly below it.  You will need to plug the second hole (below the tower).  I used 80 grit sandpaper to scuff the area then applied jb-weld and pushed a #6 x 1/4 screw in to the hole.  then used jb weld to smooth the area.  I then scuffed the nipple that the vacuum hose attaches to and applied jb weld and another screw (to block it off).  after the jb weld dries,  its time to reassemble.  I trimmed the diaphragm so that all that was left was the outside ring (i guess you could buy an o-ring if you can find one to fit) placed the ring in the grove in the back of the petcock and reattached the back.  Now I have RUN, RES, OFF.  this may be a bit confusing but I have no way to post pictures at the moment as my camera is broken

edit:  forgot 1 part--  the plastic cone attached to the valve must also have 1 of its holes plugged.  If you hold the cone with the small end facing you and 1 hole facing up and the other facing the right.  the one facing up must be plugged.  I used jb weld on this also.

[Kerry]

I have no way to post pictures at the moment as my camera is broken

Wow - like everything else at your house.  

Good job with the procedure!  

[Jenya]

This is a reply to the very old post, but I thought it may be still interesting. I followed ktrim's procedure. Except, unless his petcock is different, it isn't PRI that becomes an OFF, it is RES.
http://culbertfamily.com/jenya/gs500/petck_plugged.jpg

[Jenya]

And here is the final product! I deliberatelly stripped threads in the aluminum body of a petcock and inserted longer bolts that I could tighten very tight with nuts on the other side. I also inverted direction of bolts for estetic reasons, so that Allen bolt heads would be on the outside. Checked petcock for vacuum leaks. So far so good.

http://culbertfamily.com/jenya/gs500/petck_finished.jpg

[Queso]

So... Can you still prime? I'd like to do this, but I don't quite understand the instructions... I wish someone had pics of the actual procedure...

[Jenya]

There is no need for Priming any more. Or to look at it differently, it is always on Prime when it isn't OFF. Prime means that the fuel flows into carbs even if the engine is not running. The stock petcock acheives that by bypassing the diaphragm inside of the petcock. That diaphragm closes the hole that allows the fuel flow when the engine isn't running.

Therefore, it may be advisable to turn the knob to OFF position when parking the bike to prevent the fuel from continuing flowing into carbs when engine isn't running. Now, don't think that it is absolutelly crusial to do that. In fact, I forgot many times to turn off the fuel and nothing bad happened. If carb floats are set correctly, jet needle will close the flow automatically and prevent fuel from spilling all over the floor.

If you decide to perform this mod, which I think beats buying super expensive Pingels (sp?), and, unlike Pingles, still provides you with a Reserve position, post a question here and I can walk you through the whole process.

Jenya

[Queso]

Great! I'll be attempting this fix this weekend. I suppose I should get a new petcock gasket, then? Do you know the size of those bolts you used? That seems like a very good idea I'd like to replicate.

Also, last time I went to clean my petcock, after taking off the screws, it was still stuck together pretty solidly. Should I just use a screwdriver to pry it apart, or is there something else I should do? Thanks for your help!

[12thmonkey]

Queso, do you fully understand how to do this? i was actually about to buy some vacuum hoses and reconnect the vacuum system on the petcock (the PO disconnected it for some stupid reason...and it keeps leaving me stranded ). But, this sounds like a better solution. Maybe once i have the petcock all disassembled, it'll make more sense.

[Jenya]

Unfortunately, it isn't possible to get a replacement gasket for the petcock. It isn't offered. which means that either you should reuse an old gasket or cut a new one or use some of the liquid gasket compound or the combination of both.

I don't remember the bolt size, but I used the same as the stock. I think M5.

This picture pretty much sums up what needs to be done. Three passages need to be plugged.
http://culbertfamily.com/jenya/gs500/petck_plugged.jpg

Jenya

[Mandres]

Hey Jenya, thanks for the pic.  I think I'm going to try this myself.  I sent you a pm about your cool blue fuel hoses btw.

-M

[Jenya]

One thing to remember is to cap the vacuum port on the carb where the vacuum hose used to connect.

That is one additional benefit of this mod, IMO, ensuring that both carbs work identically. When one carb is providing the vacuum for the petcock and petcock is leaky, that carb isn't working the same as the other one.

Jenya

[Kerry]

Jenya,

Does this annotation reflect reality?

[12thmonkey]

Jenya, thanks for the post and the pictures (you make the petcock look so noble!  )

Kerry, thanks for the annotations. That helped clear things up for me, and make the helpful pictures more helpful.

[Jenya]

Kerry, it sure does.

Just to ellaborate a bit more.

I inserted a metal rivet into the PRI hole, which is top/right on teh picture.

I removed the white peforated plug from the vacuum port, which is left on the aforementioned picture.
The plug with five little holes can be seen on this picture, http://culbertfamily.com/jenya/gs500/petck_dirty.jpg
I then filled the hole with JBWeld, reinserted the plug and applied a bit more of JBWeld over it.

And finally, I tried to make a groove in the middle of the hole's wall in the plastic cone carefully with a tip of a fine diamond file, so that JB Weld would have something to grab on. I also bevelled the entry of the hole a bit. Sort of as if for countersinking. Moreover, I prepped the cone in the following way before pouring JBWeld into a cone's hole: http://culbertfamily.com/jenya/gs500/petck_prep.jpg
You may be able to see a groove in the hole's wall and a bit of a bevelling of the hole's entry.

Some of the JBWeld would be allowed into inside fo the cone and in combination with scuffed walls and bevelled entry would ensure a secure seating. After JBWeld sets, I removed some of it from the inside of the cone and smoothed both the inside and, most importantly, outside surfaces of the cone.

I hope that is clear. If not, don't hesitate to ask.

Jenya

[Queso]

Ahhh, Thanks Kerry! That helped a bunch!

I guess I'll grab some JB weld and gasket maker. So, I plug up these passages and then... PRI is off, FUEL is like prime (so it should eliminate fuel starvation with plenty of gas left issue), and RES still switches the the last bit of gas, right? So I should turn it to PRI whenever it's not running?

Seems like a bit of a pain, but if it get's my fuel system working right it will be worth it. Just out of curiousity, anyone know of another petcock that is compatible and would work correctly?

I'll with hold further questions until I've got my petcock apart, as I'm sure several things will become clearer once I'm there... Thanks for the help Jenya & Kerry!

[Jenya]

Actually, PRI will become res, RES will become OFF. So basically, when the knob is horizontal it is OFF. Up or Down and the fuel flows. It is up to you how you want to connect hoses.
You can have Down to be RES or Up to be RES. I chose Down for ON and Up for RES.

Jenya

[12thmonkey]

Another question: Does this mod convert it to a gravity-feed system? If so, how much gas would you have to have in your tank to keep fuel flowing to the carbs?

[werase643]

always has been always will be a gravity feed

about where the res tap come off the shut off valve.....so when the tank is empty...you have no fuel

the vac operation is a secondary means to shut off fuel to the carbs for dummies/lazy people

[Jenya]

This mod makes for a sort of an anti-theft device too, which I tested successfully on myself.

Before I developed a habit of turning on the fuel prior to taking off, sometimes I would run out of gas shortly after leaving a parking lot. Took me couple times of that happening to learn to recognize the problem right away and simply reach down to turn the knob.

Now, I have developed a habit of turning on the fuel automatically. I still forget to shut it off occasionally, which isn't a biggy.

Jenya

[12thmonkey]

Ohhhh. i've run out of gas several times, and still had plenty in the tank. i removed the tank, cleaned the petcock, replaced the fuel lines, and noticed that the PO had disconnected all of the vacuum lines. Didn't plug anything...just disconnected.    It seemed to run fine, other than the premature sputter and die. i figured that the reason i would run out of gas, and still have gas in the tank, was there wasn't enough to push it through.    i'm sure it's connected to the missing vacuum lines...but as soon as i added any gas, it would fire right up.

Either way, i'm hoping this petcock modification will fix that and the fuel starvation issue too.