Dumb question - petcocks

[bluedayt]

I just had the tank off while I was putting on some stainless steel bling on the motor when I thought I should check what the petcocks do because I was sure one was reserve and the other main & prime. Brian, everyone, yes I was wrong  . Maybe I should check that sort of stuff BEFORE i've had a few stubbies.......

Anyway, Brian I simply run from left petcock to right carb inlet and right petcock to left carb inlet. around 2300km and not had an issue. I guess a balance pipe might help. Maybe next time I pull the tank off....

[Eveready1100]

LPG mate.
The cylinder itself would probably be ok in a stack. The mounts and fittings would be a worry though if it got ripped off in a crash cos of the accompanying shower of sparks that nomally occur as the bike's sliding down the road. It wouldn't go bang if the pressure relief valve works, but it would throw an impressive sheet of flame from the side of the tank.

[bluedayt]

Well done.

Yeah, that looks safe....... Is it a petrol tank or Nitrous I wonder

[Eveready1100]

I found it!



I just had to share this

[Eveready1100]

Here's a thought.



Hasn't got any radical curves on it so shouldn't be too hard to fab a mock up. Also you could make it just a cover (Dunstall type) over a plain steel tank. Just bore a hole through the top for a filler cap.

Not quite as boxy as those old TZ ducktails.

[Stout]

OK, just went downstairs to check the plumbing of my occy and MelbXS is right - it is indeed the front spigot that bypasses the occy and goes staight to the fuel rail. I got it backwards.

Eveready - didn't think it was pushy at all, just thought I should explain why I'm not doing the 'obvious' thing (though I still might...) I failed to mention my seat upholstery is also quite ordinary and the shape of the padding isn't well suited to moving around as you do on an outfit. So there are a number of reasons why a hollow, fibreglass single seat unit, shaped to my bum, padded appropriately and holding about 15 litres, would work very nicely. Particularly since I'd have to make, or pay someone else to make, the tank to go under the sidecar anyway.

I'm tossing up between a rounded, tapered profile where the the pillion seat should be (like the single-seat cowls on later GSXR750s or an over-sized Norton Fastback ducktail) or a high, square, slab-sided thing with an upswept back edge as was used on the 2-stoke Yamaha bikes in the late seventies (TZ350, etc)

Any thoughts?

I plan to do some cardboard mock-ups and will create a thread when I get around to it.

[Eveready1100]

I reckon you're right on the money there, Brian. So, they're the same as a Special.
Mine was missing the octy when I bought it in 2001 and onlty realised what was missing when I had my first meet with Steptoe last year. I'd seen the mounting lug on the top of the LHS carbs but couldn't work out from looking at exploded diagrams what was supposed to fit there - cos they were exploded. Once I saw one in the flesh, it all made sense.
Stout, sorry if I was pushy with my fuel tank suggestion. Didn't realise your situation with the vacant pillion area, so I thought it would be an easier way to do it. Youll have to put up some pics of your setup once you've got it done as you've got me intrigued.
I had visions of a photo I've got around here somewhere of a black XS11 standard with a big black gas cylinder mounted across the back of the bike. Ugly as hell and just inviting disaster.

[melbxs]

Prime has it's own outlet because Prime bypasses the vacuum valve altogether so that you can "Prime" the carbs without having the engine running.

Reserve and On both use the same outlet (rear). I am 99.9% sure on this, but happy to be proved wrong.

[Stout]

It seems unlikely that Yamaha would have used two different fuel taps for such closely related models?

...and FWIW, the rear spigot of each petcock on my RH is definitely for the PRIME setting. Both ON and RESERVE are plumbed through the front spigot thanks to the tricky four-port petcock.

Why does everyone but me seem to have pulled the occy? Mine still works beautifully.

As far as putting a tank under the chair and running an electric pump goes, that is what everyone else does ;-) Seriously, that was my original plan, but it is taking me a while to get around to it (5-6 years) and I never use the rear seat anyway, so why not make up a solo seat unit that will hold fuel and gravity feed into the main? If I can execute my design well, it will enhance, not detract from, the bike's appearance while also giving me a better seat for the forces involved in riding an outfit. Also, I will always be able to just take it off and put the original back as easily as swapping any other two seats.

[bluedayt]

did you run your tank down and check if reserve worked? If yes then just run with what you've got but Steptoe's right, one outlet is main & the other one is the reserve

[melbxs]

The second one on the RH is PRIME too. I have that blanked off.

I have been running off two petcocks I was just wondering if it was overkill or not. I was driving around all day with only one tap on and didn't notice any difference.

Here is a diagram of what I run, except I have the fuel inlets pointing down and the crossover is under the carbs.

[steptoe]

that's why they call them SPECIALS,---------  -----------WE have TWO outlets on our petcocks  ,,

one does main and reserve,and passes thru the octy diaphragm,, the other does prime, and by- passes the do hickey thingy

I still have my fuel lines plumbed as original,,

[Eveready1100]

I'm not sure if the RH taps are the same as a Special, but on mine, one outlet on each tap serves as both the main and reserve feeds. The other is for the prime position which, not having the octy vacuum valve to deal with, is superfluous so I've blanked them off with short plugs to tidy up the area a bit. Makes life much easier when removing and fitting the tank.

[bluedayt]

Brian,

I run both pipes from both petcocks but don't run the octy thing. I have run two pipes from each petcock up to a Tee piece, then 1 pipe from there down to the carb inlet. The left petcock feeds the two right hand carbs and the right petcock feeds the left carbs. I can take a photo and send it to you if you wish. I might be stating the obvious here but just in case - each petcock has two outlets on it, one is for normal and the other is for reserve so if you use only one then you may come into all sorts of issues. Doing it the way I have gives you use of the entire tank including reserve (which I had to use while on the way home from StAndrews on Sat).

[melbxs]

No Octy and I had the lines in an H shape with a crossover between the two feeds. I was thinking it would be simpler to have a single feed split under the carbs to the two inputs?