octy/petcock debate?

[mjpxs11sh]

ive been reading the threads on petcocks, fuel leaks, and octy and am a little confused. i stripped my 81 Special fuel tank parts off today to prep for a new blk with goldleaf repaint. when i was draining the fuel, i checked the function of the frt/rear petcock outlets with fuel hoses disco'd. heres what i found, engine off. i have no issues, leaks etc. just was checking where fuel flowed out w/ tank removed from bike. it runs great after repairing all normal xs11 leaks with carbs, etc.
position flow
off= none
on= rear flow
res= rear flow
pri= front flow

is that correct? maybe i misunderstood what i had read previously. i thought someone posted fuel should not flow from the petcocks with the engine off and petcocks in on/res positions.
does that mean just out of the octy to the carbs, or out of the petcocks themselves with or without fuel lines attatched? please help me clear my mind. thanx

[bikerphil]

If you have the octy, it controls the on and reserve positions. No engine vacuum, no fuel to the carbs. The prime position bypasses the octy thru a T in the fuel line directly down to the carbs, vacuum not needed.

off none
on rear flow
res rear flow
pri front flow

The above is correct.

[crazy steve]

...does that mean just out of the octy to the carbs...

That's what is meant. If the octy is in place and working right, there's no fuel to the carbs with the motor off. With the motor running and vacuum to the octy, then fuel can flow depending on what position the petcocks are set on. Unless it's 'prime', that setting bypasses the octy and you get fuel flow to the carbs at all times....

[trdriver71]

I think he means he has the tank off the bike and just tested the petcocks and yes they are working right.

[mjpxs11sh]

petcocks

thanx guys. maybe i wasnt clear. my question was about the petcock flow without fuel lines and tank off of bike. so if i have it right, fuel will always flow out of the petcocks, the only way to stop flow is in the off position, which means in on/res position, fuel flows to the octy when lines are connected, engine off, but the octy diaphram stops the flow to the carbs. in prime position, fuel flows into the T's, bypasses the octy and goes directly into the carbs. is that right, which means my flow chart is correct, right?

[bikerphil]

You have it correct.

[mjpxs11sh]

petcocks

thanx trdriver71. thats what i was lookin for. u must have replied while i was typng.

[DGXSER]

Not to confuse you, but to keep things clear for those who are or might be later following the thread, this is all true on the Special models.

Perhaps you read something from a thread on a standard tank, which operates a little differently. On the standard tank, the vacuum diaphram is built into the petcocks. On those, the petcock itself will only flow fuel in the prime position without vacuum. The ON or RES will only flow from the petcock with vacuum applied.

[mjpxs11sh]

right

u hit it on the head. thats what i read and ive had those petcocks apart and couldnt figure out what was would hold the fuel back since the washer has 4 holes in it.

[dodjh]

octy/petcock debate

I want to eliminate the octy: how do I run my lines?

Thanks

[DGXSER]

There are more than a couple answers to that question. I am a fan of the KISS method, so I put a plug over the front outlets on the petcocks, and then run the rear outlet to an inline fuel filter and straight to the carb inlet.



Depending on the year of your carbs, you may not have the vent shown in purple, mine do not. The fuel filter is a $5 filter from any local bike shop.

[fredintoon]

I want to eliminate the octy: how do I run my lines?
Thanks

Hi Charlie,
I'm with DGXSER, the simple way is the best way.
But you need to remember that once you have deep-sixed the octo the gas taps are on manual. You gotta remember to turn them off whenever you park the bike just like Grandpa on his Norton.
Not remembering to turn them on again will become self-evident in about a quarter-mile. In my case that's just about at the nearest traffic light. See the old fat guy die of embarrassment.

[dodjh]

octy/petcock debate

Thank you for the diagram...and explanation....I believe that is how I will set mine up.

Charlie

[Shockman54]

still not clear to me.

ok, i understand where to run the fuel lines, what do i do with the tubes running out of the carb boots and the vacuum tube? btw, this is on a 79 xs special. i am planning on eliminating the octy, at least for now. i also need to know what to do with the large tube running from the back/top of the engine that went into the airbox. i believe its called the breather hose?

[Danny Crawdad]

Just remove the vacuum hoses, and cap off the nipples at the carb boot. You can buy vacuum caps at any auto parts store. I just routed my breather tube along the frame, but there are probably some better suggestions.