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Discussion Starter #1
I have a 95 shadow VT600c with a vacuum problem.

Bike only idles on choke. Will die when given throttle.

Carbs are clean however...

There is a vacuum hose coming off the top of both carbs that goes nowhere. Off the top diaphram cover there is an hose coming off each one that goes to a T then goes nowhere. It is pulling vacuum and if you close it/cap it off the bike will not run under any circumstances.

I am at a loss for the service manual and cannot find a vacuum diagram anywhere. Any help is appreciated.

Thanks
 

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overtwocustoms said:
I have a 95 shadow VT600c with a vacuum problem.

Bike only idles on choke. Will die when given throttle.

Carbs are clean however...

There is a vacuum hose coming off the top of both carbs that goes nowhere. Off the top diaphram cover there is an hose coming off each one that goes to a T then goes nowhere. It is pulling vacuum and if you close it/cap it off the bike will not run under any circumstances.

I am at a loss for the service manual and cannot find a vacuum diagram anywhere. Any help is appreciated.

Thanks
That tube is not a vacuum tube, it's a pressure vent for the carburetor slide piston.
The diaphragm has to have a vent or else it will try to compress the
air in the chamber above it when it lifts.
That tube is vented to atmosphere and allows the pressure in the
piston chamber to escape to allow the piston to move up and allow
fuel in to the venturi of the carburetor.
You might have one or both of your piston diaphragms torn
or have a hole in them.
 

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Discussion Starter #4
If I put a vacuum bleeder to the line going into the top of the carb should it hold that vacuum pressure or not?

i am a bit confused as to the diaphram you are talking about.
 

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overtwocustoms said:
If I put a vacuum bleeder to the line going into the top of the carb should it hold that vacuum pressure or not?

i am a bit confused as to the diaphram you are talking about.
Read 'Litnin's post again.

If you are both talking about the SAME hose.......there should NEVER be any vacume there (or pressure either, for that matter) except for the instant that the throttle is opened or closed and even that would be mostly undetectable.

The diaphram is inside the carb.
 

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overtwocustoms said:
If I put a vacuum bleeder to the line going into the top of the carb should it hold that vacuum pressure or not?

i am a bit confused as to the diaphram you are talking about.
Inside the bore of each carburetor is a slide piston.
That slide piston has the needle for the main jets on it that go down in to a seat.
On the top of that piston, there is a rubber diaphragm.
When you open or close the throttle, air pressure differential either causes
the diaphragm to move one direction or the other.
As the diaphragm moves up, it pulls the piston up, which also pulls the
needle up out of the seat and allows the fuel from the float bowl
to be pushed up in to the venturi of the carburetor.

When you let off the throttle, the pressure differential changes again
and allows the diaphragm to relax (assisted by a spring) and the piston
goes back down and the main jet needle seats and stops fuel flow from
the main jets. All of this is variable, based on throttle position and
vacuum increasing and decreasing.

If you look on top the carburetor, you'll see a metal cap about 3 inches in diameter.
Under that cap is the diaphragm.
There is a o-ring groove in the carburetor surface.
The diaphragm seats in that o-ring groove and the cap seals and holds it in place.

Without that vent tube on the top of the carburetor,
as the piston/diaphragm moves up, the air trapped above it would
be trying to be compressed, which would prevent it from moving
it's full length of travel and try to push it back down.
The vent allows the air to escape so the piston/diaphragm can move it's full intended travel range.
 

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Discussion Starter #7
I am familiar with that diaphragm. I have inspected it and cannot find any holes or tears in the diaphragm itself. Everything looks to be in great shape. I understand how it works pulling vacuum from the engine. With the engine running the vent hose is sucking air, a substantial amount of air at that. The bike will idle only with the choke on, any hint of throttle or closing of the choke and it dies immediately.
 

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overtwocustoms said:
Attached is a picture with the 2 "vents" in question just to be sure we are talking about the same part.

Good idea posting the picture.
No, we aren't talking about the same vents.
The big black tubes on each side is the one I was referring too.

The ones you posted look like evap purge lines.

Is your bike a California bike?
These look like the hose connections that go to the evap control valve
on a California bike.
Federal bikes do not have these.

Look under your left side cover.
There *should* be a vacuum hose routing diagram that shows where each hose goes.

If you have bought carbs from a California bike and put them on a federal bike,
then you can just cap them.
If it's a California bike, they need to go back to the purge control valve
 
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