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How to size a petcock?

14K views 24 replies 9 participants last post by  Eye_m_no_angel 
#1 ·
I just got a project bike that I've been working on fixing up and I need some advice with. The inside of the tank was very rusty but after some vigorous aquarium rock shaking and a couple coats of redkote that part is taken care of.

Thing is there is no petcock that came with it and I'm kinda new to motorcycle repair so I wanted to ask how to know what kind and what size to get? I can't find alot of info online about it.

It is not the screw in kind its the bolt on kind with two bolt holes on the ends of a oval shaped hole. Are these all the same size or are there different sizes like this?

The bike itself runs great and the bike is actually three bikes, the front is off a 71 shovelhead, the engine and frame is off a 81 yamaha xs1100h, and the rear is off a shaft drive honda. I don't believe this is the original tank because it looks like the guy I bought it from welded some stuff on there for the bolts to go through. He just let the tank sit for too long in his garage in the open humidity and it rusted inside. Any advice is appreciated.
 
#6 · (Edited)
Any chance you can post a few pics of the tank? Good chance I can ID the tank and then tell you what you need. The term "petcock" originated in England many moons ago. It was a slang term that was used because the Brits call gas "petro", and they referred to many types of valves as "cocks"..."petrocock" got shortened to petcock. Some manuals refer to them as fuel valves or as Eye pointed out, "fuel selector valve". There are many japanese bikes that use what you are describing. A pic of the area where it attaches that also has a ruler along side the holes would also be very helpful.
 
#10 ·
The term "petcock" originated in England many moons ago. It was a slang term that was used because the Brits call gas "petro", and they referred to many types of valves as "cocks"..."petrocock" got shortened to petcock.
That explains it, and thanks for posting. I never made the connection between "petrol" and "pet." Very cool!

And not worth much, but in German a petcock is called a Benzinhahn. Benzin = gas, and Hahn = Rooster, or, "****."
 
#8 ·
Actually Moni... when it comes to motorcycle mechanic's shop talk, there are lots of terms we use that we don't even think of as "naughty". For instance, when we talk about electrical connectors, we refer to them as mates. One is female, the other is male. I guess cuz I deal with bike repairs 6 days a week I don't think anything about the word petcock. I need to get out more!!! lol
 
#9 ·
Yep, I know all about the male/female terminology...but when you put 3 (1 has to be separated) of the title words together in the same sentence it tends to "stand out". LOL!!! Anyway, I better stop before this thread has to be moved to the Bar. :D :D
 
#21 ·
I KNOW, Right??? Funny thing is Moni, that every thread you post in has a sense of niceness in it. You really bring a lot to this forum. As do ALL the regulars. For a brief while there ya'll didn't hear from me. Yeah, I was all busy and all that, but I honestly missed bantering with everyone here... Hence my sudden "re-visibilty". I missed you guys. Well, tis good to reconnect!!!



:71baldboy:
 
#20 ·
Dragoon.... Sorry for the delay getting back to you. Great pic of the tank!! It helps a lot. Based on the pic, you actually have many petcocks to choose from. Kawi, Yamaha & Suzuki all have used that same layout. But here's where things get complicated. The original 1981 XS1100H had a complicated fuel delivery system. That bike originally had 2 petcocks, 1 on each side, and then a vacuum controlled fuel valve in between the tank and carbs.

First question: Does your bike have an inline electric fuel pump?
2nd question: Does your tank show evidence that it used to have 2 petcocks?

Here's why I ask these 2 questions:
A bike that uses an inline electric fuel pump does not need a vacuum controlled petcock. The fuel pump itself IS the valve.

If your tank was an original XS1100H tank, you'll have a problem if someone welded a plate over one of the petcock mounting areas. That tank can't distribute fuel from 1 side to the other. That's why they used 2 petcocks.


Here's the good news...

You have a multitude of petcocks that will fit that layout. If your bike has an inline electric fuel pump, you'll want to use a petcock from maybe a mid 90's Suzuki Intruder (not the 1400) VS700, VS750, VS800. If your bike has no inline electric fuel pump, then Yamaha is your answer. Any 1992 thru 1998 Yamaha XS750 or 1100 will fit.

Dragoon... That is one helluva Frankenteined bike... would love to see pics of her!! Please keep us updated of her progress, sounds like a really cool project!!
 
#22 ·
We're glad to have you back. I wondered what happened to you. Lots of folks join the Forum and after a few posts or a few months of regular posting disappear. I often wonder why or what happened to them.

I always appreciate you mechanically minded folks. I often learn from some of the things you tell others. Thanks for helping us and Don't be a stranger again. :)
 
#24 ·
Thanks for replying Jack! The fuel line goes straight into the carb and there is no fuel pump that I can tell. There was just the one fuel line and I have it hooked up to an old lawnmower gas tank right now just so I can crank it periodically. I don't think it is the original tank either. It looks like some mounts were tac-welded on the bottom of it to match the holes in the frame.

So it looks like Yamaha is the way to go thank you Jack the help is much appreciated man. I'll post some pics when I get finished. There is really not that much left to do to her now. I have to finish sanding and painting my gas tank and parts of the frame and get some wheel bearings (i think i might as well do both front and back at the same time, no telling how old they are) and she'll be ready for the road again.
 
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