Modified Vacuum Petcock Blues.

[patk12345]

I apologize in advance, I searched some of the threads, but there were soooo many related to petcocks, I thought I would put my question directly to the forum.

Okay! My bike has vacuum petcocks, with modified tubes that were sealed under vacuum pressure to keep the vacuum diaphragm always open. (I'm assuming this is what is going on as I got the bike this way, but friends who have seen this seem to agree.)

So, when the bike is parked, the carbs will overflow into the air box and fuel spills out onto the floor. My question is what position should the petcock be in when the bike is parked PRI, ON, or RES? Or because of the addition of the modified "permanent vacuum" tubes, will it leak in any of these positions?
Any ideas, why the vacuum tubes might have been modified, e.g. are the standard vacuum tubes problematic? What should I look out for if I reconnect the standard vacuum set up? Can I switch over to a non-vacuum activated petcock, and if so, is there anything special I need to do?

Thanks again.

[DAVINCI]

Modified petcocks or not, if you're getting fuel leaking into the airbox, your carb float needles / seats are leaking.

[cywelchjr]

Without knowing how the person who modified them did the modification did it, there isn't really a way to know what position they need to be in, but to start with, if you get gas out of the airbox, you very likely have gas in the oil and will trash the bearings if you don't change the oil and fix the problem with the carbs right away. To get leaking from the carbs requires two things, leaking petcocks, and leaking needle valves.

It's unlikely that the vacuum tubes were sealed "with vacuum in them" as nothing rubber like a diaphragm is a perfect seal, so they would not stay activated. So likely the person in some way bypassed the vacuum portion of the petcocks (there are a couple of ways it can be done, only one of which I know of gives an actual off position). It helps to give the model and year of your bike in your tag line as it helps us to better answer your questions (you could manually put that in each question, but that's a lot of extra effort) more accurately.

[patk12345]

@DAVINCI

But if I can get the gas to shut off, I can put off rebuilding my carbs a little longer. I need at least one day of riding the cursed thing before I start wrenching on it again. That or maybe I'll buy some snazzy new bike, with fuel injection, digital ignition, water cooling, and anti-lock brakes. But why would I do that when I can wrench and wrench and wrench and wrench and...Oh! Sorry, you mentioned something about carburetors.

[patk12345]

@Cy

Sorry, I thought my bike model was already in the signature. I will rectify that immediately.
By the way, it's a 1980 XS11 Special.

[WMarshy]

While everything they said is true this link is the most cost effective petcock solution.
http://www.xs11.com/forum/showthread...ht=petcock+mod

That being said, you still need to check for oil in your gas, could make wording about leaky carbs a mute point if you spin a bearing... GL!

This mod only works if you have the older style pet cocks...

[WMarshy]

... you still need to check for oil in your gas...

Er... gas in your oil... been up for nearly 20 hrs, can't tell if the glass is half empty or half full...

[patk12345]

@WMarshy
Thanks for the link! It looks like a good potential solution to the immediate issue. I'm a in a little over my head, when it comes to carbs, vacuum lines, and all the rest. I need to just grab my kayak and hit the damn river. If it floats your good.

[cywelchjr]

@Cy

Sorry, I thought my bike model was already in the signature. I will rectify that immediately.
By the way, it's a 1980 XS11 Special.

Ok, specials don't have vacuum petcocks. Unless someone put a standard tank on, they have petcocks with two outlets, one that works in the prime position, and the other that works in the on and res position, and neither works in the off position. If you don't have 4 positions on your petcocks, then something has been changed and isn't the way it came from the factory for the special.

It sound like though that the previous owner (called PO) may have removed the Octy which is the vacuum operated fuel valve that comes on the specials in stock form, this is actually a pretty common modification, and it's generally recommended in that case to always put the petcocks in the off position when stopping, but you still need to fix the leaking petcocks, which on a 1980 if it's not been done probably needs the o-rings on the needle valve seats replaced as those wear out and let gas seep right past the outside of the needle valve seat.

[cywelchjr]

While everything they said is true this link is the most cost effective petcock solution.
http://www.xs11.com/forum/showthread...ht=petcock+mod

That being said, you still need to check for oil in your gas, could make wording about leaky carbs a mute point if you spin a bearing... GL!

This mod only works if you have the older style pet cocks...

Being that he has a special he should have the off position already. But if his tank has been swapped for a standard tank, then this mod would be a good one for him, that or Davinci's mod (although the one you pointed out is a good bit easier to do).

[fredintoon]

- - - By the way, it's a 1980 XS11 Special.

Hi Pat,
A Special left the factory with gas taps that say:- off, res, on and prime.
Then there's at least 8 hoses that run to the carbs via a single vacuum operated valve; the dreaded octopus.
What's there now, who knows? Many have changed that set-up over time.
However, the gas is running out because one or more of the carb float valves ain't working right.
This is bad because not only will that make the bike run rich when it's running, it will let gas run into the oil when it's stopped.
You don't want that.
So, 2 fixes.
1) Fix the float valves.
2) Find an off position that works on the gas tap configuration that you have.

[DAVINCI]

Yeah, what Fred wrote

[natemoen]

A picture of your petcocks and pic across the top of the carbs could help too.

[Jamie]

From first hand experience, don't like gas on the floor in the garage, or in my crankcase. PO had put wrong re-build kits in and I got to experience his inability to read part numbers. From here on out, this will be a annnual (winter) or at least every two year service to my bike. Piece of mind is what I'm talking about. Here are some pics of my XJ vacuum petcocks and also I will be tearing down the Octy at the same time (I'm one of the rare guys who use and love the Octy).

[DGXSER]

Jamie, those are pretty much if not exactly the same petcocks as used on the Special models. They are not, however, vacuum petcocks.

The Standards use a petcock that has a similar vacuum operated daphram to the one in the octy. In esence, they have tow octy valves, one on each side. Those are the vacuum petcocks.

HERE is the thread I put together on rebuilding the petcocks and the Octy. HTH.