Vacuum line on stock petcock. Whats its purpose??

[JaysGone]

Im pretty new here and have a 99 Valk "F".
It took 3 wrecks to rescue the bike I currently have.
I bought it as a non running bike for a future trike project.
7 months later its a rat bike OK, but runs well.
Ive put a 1000 miles on it.

I have no vacuum line on the stock petcock.
The engine Im using had been desmogged.
The engines been totally cleaned up.
All vacuum ports incuding the manifolds have been plugged.
The bike does indeed run well.

My question is this:
Is it 100% needed to have a line connected to the petcock vacuum port??
If so why??
What difference does it make??

Ive read all the posts here searching I can in regards to this and didnt see what I want to know.
The OEM manual has been of no help on this.
Jay

[Skinhead]

On an unmolested OEM petcock, The vacuum line supplies engine vaccum to a spring loaded, normally closed diaphragm valve that shuts the fuel off to the carburetors when the engine is not running (no vaccum, valve closed=no fuel            engine running, vacuum, valve open=fuel flow)

That is normal intended operation.  The petcock can be modified to function manually (no vaccum line), I suspect yours has been modified.

I believe Graphon rider? may have posted a procedure on the modification details.

[Chrisj CMA]

If you have a stock petcock and it runs at all without a vacuum line, then the petcock is toast.  Get a manual (non Vac) petcock and that may be all thats needed ot get her running like a scalded dog

[JaysGone]

The bike runs pretty darn good.
Plenty of power and all.
Thats not an issue.
Im very happy with it actually.

I just went back out to the garage and looked at the petcock again.
It does have a port for a vacuum line.
Its just open, not blocked off.
I did have the petcock disassembled at one point to clean it.
The spring and plate are indeed in there.
Its a fairly simple straight forward deal.

If it does need vacuum for the valve to open.
Then my bike in its present state shouldnt run.
I figured gravity was just doing the job.
The petcock appears to all be there, with no modifications to it.

What got me started on all this is in 4th gear.
I do have a very little bit of a stumble in the engine when just cruising at 50ish mph.
So the 1st place I start looking is the fuel system.
The lack of a vacuum line is the only thing I saw.
I thought of that might be a part of the problem.

As it sits it runs fine.
It is indeed shutting the fuel on and off.
The reserve works too.
I know I could just add a line and see what it does or doesnt do.

[Bone]

There are different methods for converting the petcock to manual, reserve still works. Mine doesn't have the diaphragm. Some guys are putting the spring on the opposite side of the diaphragm and that keeps it from sealing off the gas flow.
So all of the parts may be there but not in working order.

[Chrisj CMA]

Heres the deal.  If it runs with no vacuum then the vacuum side of the petcock is not working.  Are you sure theres not a vacuum line and what you are looking at is the weep hole.  There is a "port" as you say pointing straight down, thats just a weep hole, the vacuum line is parallel to the fuel line and easier to miss.

If it is indeed running without a vacuum line and hasnt been modified then the vacuum shutoff is obviously inop and Id be suspect that less than the neeed amount of fuel is flowing.  Adding a vacuum line may not help because theres obviously no seal for the vacuum to work against.  

The OEM petcock barely satisfies the fuel needs for the old girl when working properly.  Any malfunction and you cannot rule fuel starvation out because the petcock usually starves the motor when its going bad

[JaysGone]

I can see the right side of the petcock clearly.
Its the paralell little port pointing forward that should have the line on it.
I cant say for sure whats where on the inside.
I opened that up last July when I got the bike.

Ive looked at the Pingles that are suggested for this bike and cant see how you can reach in there to use it............
Plus its costs.............
As a second bike, I dont want to shell out the $$ for a pingle.

Maybe Ill go for a rebuild kit or a used OEM.
My only fear is the way it is now.
Knowing its wrong.
I stand a good chance of getting stranded someplace in my near future.

[custom1]

Here is Gryphon's excellent post.


http://www.valkyrieforum.com/bbs/index.php/topic,40666.msg385628.html#msg385628

[Patrick]

It certainly sounds like yours has been modified for manual usage , so , to me, the question is - does it work correctly ?? Does fuel actually quit flowing when you shut it off ??  If it doesn't, spend the money for a Pingle or a new Honda valve..
If you ever touch the starter button and you hear a 'CLANK' , DO NOT , touch that button again until you clear the cylinders..

[GJS]

You do want to tend to this!
If you were to have one of your 6 carb floats get stuck, you'd get to learn about hydro lock.
Fuel pours into a cylinder, you try to start, your starter motor sheers off sprocket teeth trying to compress gasoline. Has'nt happened to me, but you have one of the two failures involved in making it happen. (there are many stories of the dreaded hydro lock in the archives)

Good news is, all you have to do to solve the problem is......
Shut off the valve manually each time you remove your keys. Easy fix.

Good luck

Glenn

[JaysGone]

Get to know Hydro Lock??
Im a pro at it.
I went through 4 gallons of oil before the bike was ever ridden.
3 sets of carbs before I found 6 that were good enough to use.
A fork oil suringe works really well for draining a cylinder full of gasoline through the spark plug holes.
Been there redid it many times.

Which is how I know the petcock is actually in the off possition when it says so.
Now............

[JaysGone]

Here is Gryphon's excellent post.


http://www.valkyrieforum.com/bbs/index.php/topic,40666.msg385628.html#msg385628

Thanks for the diagram.
According to this the right side plate is indeed on in the wrong posistion.
If I did it during my cleaning and reassemble?? No clue.
But it has the vent line forward, paralell to the fuel line.

Im ordering a rebuild kit today. Whether I actually need it or not.
Will see whats what when I have the stock petcock apart.

[JaysGone]

Yup it was modified guys.
To run with no vacuum.
All in there more or less set up backwards.

[JaysGone]

I hope this works otherwise its just crap.

Heres the bike as I bought it none running.
A purple that was welllllll disgusting.
The other picture is rather recent.
Ive removed all the paint less the wheels and rattle canned a few places.

So for thos that asked I hope they come out OK.

[tank_post142]

looks much beterer