Quick an easy petkock mod (for confident mechanics only)

Petcock iffy? Here's what I came up with. This will make it an on - off - reserve type with no vacuum line.
First remove it or the tank. Might can do it in place - don't know.
Take off the back (vac) side and look at the parts to make sure you have one good diaphram and a good o-ring on the plunger. remove the fiber spacer ,double up the diaphrams (look for good edges on them) and put it back together without the spacer but do use the spring. CAUTION..one of the screws will be too long and will interfere with one of the petcock mount
screw's gasket. Add two small flat washers to keep it from going through so far. For good measure cap the vacuum barb and don't forget to cap the manifold barb as well. Ok , through with the vac side.
Now remove the two little front screws and rotate the petcock handle and the retaining cover 180 degrees and the refasten making sure the wavy spring washer is in place behind the cover plate. ON is up. RESERVE is to the rear and OFF (PRI) is forward. 8) That's it and good luck! Almost forgot. When you bend over to check what it's set on the letters are no longer upsidedown :wink: NOTICE: the selector has to be shortened to clear the tank edge.

PARTS LIST - 2 #6 flat washers (#8 if the#6 is the tight kind)
PS: petcock is spelled wrong in the topic line be cause it gets "edited" if spelled correctly. Program must think it's a no no bad word.

 

Re: Quick an easy petcock mod

wait....

can you just plug the vac line and use PRI as on and on as off?

 

Re: Quick an easy petkock mod

Ask wizard. I think you have to pull out the filter tower and rotate it 180 to make it work and it will still be Off when in ON. And he also glued the middle hole closed. See Brushy's writeup on this.

 

Re: Quick an easy petkock mod

gas WILL NOT come out of the hole when it is on "ON" unless there is suction to the vac hole, so if you plug that hole it wont come out, and then when on PRI it is a gravity flow.


my question is why do that mod unless you have a broken petcock?

the vacuum fuel flow system on these yamaha's work just fine, unlike the SOS (spawn of satan) setup on DOHC cb750's.

having a gravity flow could potentially fill your crank case with gas if you forget to shut if off...

just a question, not raining on your parade, I know some people would probably prefer a simple on off petcock.

(bobbers come to mind)

 

Re: Quick an easy petkock mod

A Quick And Easy Petkock Mod?
That is necessary because, ... ???

Because there aren't enough Garage Floors saturated with Gasoline?
People need their Fuel Tanks drained down into their Crankcases?

Oh, look. If you do this, all the safety measures ingeniously Engineered into a component part will be averted and bypassed rendering the assembly completely unsafe and dangerous!!!

http://www.amazon.com/MIDWEST-ENGINE-WA ... B00307BCCU

 

Re: Quick an easy petkock mod

Bit of a harsh reaction, don't you think? Vacuum petcocks have been known to fail and pour gas straight into the manifold through the vacuum line (one of my old 900's did this).

At least with a non-vacuum tap you only risk flowing fuel into the carbs / airbox / sump ONLY if you accidentally leave the tap on (and then ONLY if the float valves are stuck open).

 

Re: Quick an easy petkock mod

Read ...think... then start typing. With the vacuum line removed no gas can return to the engine.
If you turn off the gas no gas can go to the engine.
If you select ON it is ON ( no vac required)
If you select RES it is RES
If you select PRI it is OFF
Two out of three ain't bad. Also the spring is pushing a little harder with the spacer gone. If it leaks through any then your no worse off than with the original setup and finally...if you don't like it then don't do it.

 

Ah, the first 2 words....

yes, I think that would be a smart mod if you're petcock was iffy and you didnt want to rebuild


my bad, carry on

 

Nope.
Not harsh.
Honest to God truth telling.

The old Petcock lasted almost 30-years.
Lest say a new one costs $400.00.
That's roughly ... One dollar and 9-cents a month for safety!

But, they don't cost $400.00
That means you will have to spend less than a Buck a month for the peace of mind for buying a new one.

There are things that just ain't meant to be modified.
And with the down-side far outweighing the up-side ... somebody has to rise and be the voice of reason and ... while not using any swears ... try to explain why parking an armed bomb in your garage that could go-off and burn-down the house and everybody in it ... really ain't such a good idea at all.

Any young first-year Engineering Student should have seen the obvious problems this modification is fraught with and brought forth some solutions other than getting giddy about it and recommending it employ.

 

I've had a vacuum tap fail on me without warning and pour fuel through the vacuum hose into the cylinder.

Can't say I've ever had a manual tap fail on me.

So, if your talking about time bombs, a 30 year old vacuum tap is more of a time bomb than a manual tap IMO.

 

Hey Rick. What if you aren't going to be around another 30 yrs? Then your premise is flawed from the beginning.
And actually, everything is meant to be modified. If it wasn't, we wouldn't be here (online/phone), discussing motorcycles (bicycles) with our computers (quill pens).
I'm new to this site, and this type bike, but I'm not new to bikes. And I've found with my considerable time on this earth that listening to an idea, however strange, is still worth listening to.

 

My petco' was leaking past the diaphragm O ring, got complete new innards for it from Chacal everything was clean, in tank filter intact, put it all together properly. It still leaked, took it apart checked everything, put it together, it still leaked. Did a mod' (but a different method to seaguy) it doesn't leak!!
Now there are only 2 parts to wear and if it's not turned Off that's my fault not some mechanical failure.
None of my other bikes had the vac' line they didn't leak. Problems with the petco'/ vac' line are very common on this site.

 

this place is really starting to get irritating with the whole "modified is evil, stock is best" state of mind. ugh.

 

Wow!

Have you guy's forgotton that we're friends with a common
goal and intrest?

Rick has offered years of good advice, so jumping down his throat
for a disagreement at what he feels is a danger to your safety
is just wrong.

Seaguy has come up with a good mod idea for those who need a
solution to a probem. If that idea does'nt sound like something
you want to try keep looking or go stock.

In any case, no need to act like we're still in high school.
(even if you still are lol)

 

What I failed to mention and some might not know the original plunger o-ring actually isn't a true o-ring. The side that seats has a taper to it and provides more contact area. The kit o-ring is standard type. The original one is no longer available according to the guys at Mikes XS. So if your Oem o-ring is bad then this mod will not work correctly. The rear half or o-ring seat area would have to be epoxy filled or a non gas reactive rubber plug in the center passage to block flow to the outlet.
If you rebuild with a kit that has an O-ring instead of the oem type seal then your doing a MOD. The only reason I mentioned this variation of a simular mod was to show a way to do it without having to mill the selector,drill more holes and tap the center passage for a sealed plug.

 

haha calm down everyone.

on/off petcocks are some peoples choice, they like the simplicity, for others its a choice, like ALL DOHC cb750's, the vac system just DID NOT work.

Though as long as your normal petcock works, theres no reason in my mind to change it over, its so carefree.


Ok, continue waging the war

oh and as far as first year Engineering students coming with an alternative solution rather than jumping on the unsafe bandwagen, here is my solution



Just adapt the vac's hose to fit the vac nipple on the petcock.

then run the fuel line to the carbs, pull the shop vac wherever you go, and you have a super failsafe, 1 fuel will not flow unless the vac is on, and, if the vac line starts to drain fuel, then it will gointo the shop vac and not into the engine!?!?!?!?!!?!?~!?!?!?!?!

 

Whatever you're smoking... I want some.

 

did you mean to say.""

 

Hey schooter, that vac will go nice with your new
jacket if they ship the one with orange in it. :wink:

or..........you could represent all the citris if it's yellow :lol:

 

That DVD rewinder is awesome.... I gotta get me one. No seriously, that would make a great gag gift for some friends.

 

Is it possible that a round "O" ring would flatten out after 28 years?
Is it also possible that a regular "O" ring would seal just as well?

 

Yes and yes,as long as you have the unit with good machining alignment as mentioned in the Mikes XS writeup.

 

I elimated the vacuum from mine and the original positions work as intended. But I don't remember how I did it.
I remember capping the front outlet but I don't remember the rest.
If anyone is interested I will try to conjure up the details.
I just wanted it simple. Oh and BTW I don't bother to turn them off
because they have never leaked ( so far). The only time I mess with them is when I need reserve.
(You have to say so far in the same breath or it will screw up immediately!)NEVER let a vehicle know you trust it.

 

hey guys let me throw something in the fire . those of you who know what can happen when you fill a cyl with liquid it doesnt compress it bends rods breaks pistons and if you should be lucky enough to not break anything and dont catch it it will also wipe out rod bearings. I can see the points both ways but it scares me not knowing for sure . i have recently had it happen to my virago and it allways happens at the worst time like when your headed out to work ect . and there is no way to stop it other then draining the tank. pulled the plugs cranked it over shot gas 10 feet its not pretty . i bought a new petcock plumbed a manual petcock on the vac. line so i could shut it off and run the gas out . darned if it didnt do it again a few weeks later did it again i think the float on 1 carb is sinking from sitting so long . i neep to pull off the float bowl check it . if it wasnt for the fact i bought a hi flow valve to splice into the line i would do it .

 

Am I missing something here? Two days ago, Schooter was going to be an Engineer, driving a locomotive but today he is getting tooled up like a ghostbuster.

Whats going on?

 

im with dwcopple

 

Thought this was the "Mods" section.. If you don't like modified, you're reading the wrong section..

At the end of the day, information about how to modify any part of your bike should be posted here.. If you can see some inherant dangers, by all means post them, but we're all adults, if we want to take a risk, that's our look out, they're our bikes, we can do whatever we choose to them, don't "mommy" people, it's insulting.