Topic: CL350 & CB450 CV carbs springs and diaphragms

[greenjeans]

I have a 72 CL350 and a 72CB450 that I'm working on.  Both have CV carbs that are very similar with 1 main difference.  The CL has a rubber diaphragm, the CB has an aluminum type diaphragm (no rubber).   The one with the rubber diaphram makes sense - It has a spring to keep the slide pressed downward.  But, the CB has no spring.

Is it just the weight of the aluminum piece that returns the slide to its closed position ?   Somebody school me.

[cb650]

all I can add is that the CV's on the 650 have the aluninununum plunger with a spring.   Very light weak one but they are there. 

[tbpmusic]

450 carbs use no springs, just gravity and vacuum - however there was a retro-fit spring added for some 4-speed 450 carbs, which originally had no slide springs.
The spring was eliminated in the 5-speed series of carbs, starting with the 14-H types.
When kept scrupulously clean, the 450 carb is a brilliantly simple device, Honda used that basic design for decades on many different models - of course they inevitably added all sorts of unnecessary crapola (including springs) to the design as time went on. Just examine a Gold Wing carb - same basic design, but a lot of extra "stuff".
They (450 carbs) tend to be very tolerant of exhaust/air filter changes (unlike the 350 carb), and have a degree of immunity to altitude effects (also unlike the 350 carb), just due to the principles of their vacuum-based design.
Interestingly, all the fuel for both main and idle circuits first passes through the main jet on a 450 carb.
Early 5-speed types (14-H) used 130 main jets, later types increased that to 140-145, as pollution mandates and exhaust changes caused modifications to be required.
The only miss is that there are no vacuum ports on either bike (450/350). Many of us install vacuum ports on our own 450's, which allows razor-sharp tuning.

[greenjeans]

Mine have what I assumed was a port for synching.  At the diagram, it doesn't have the part for the screw listed, but it does for the washer.  (part #1)
I wonder if I were to add light spring to them?     These are shockingly clean though.   I guess I like a positive snap to the throttle.

[tbpmusic]

Mine have what I assumed was a port for synching.  At the diagram, it doesn't have the part for the screw listed, but it does for the washer.  (part #1)
I wonder if I were to add light spring to them?     These are shockingly clean though.   I guess I like a positive snap to the throttle.

There's no vacuum port on a 450 carb.
Adding a spring would most likely screw things up.
Take a soda straw and blow into one of the holes around the carb intake opening - the side should easily rise up, then fall back down. If so, you're golden.

[greenjeans]

Mine have what I assumed was a port for synching.  At the diagram, it doesn't have the part for the screw listed, but it does for the washer.  (part #1)
I wonder if I were to add light spring to them?     These are shockingly clean though.   I guess I like a positive snap to the throttle.

There's no vacuum port on a 450 carb.
Adding a spring would most likely screw things up.
Take a soda straw and blow into one of the holes around the carb intake opening - the side should easily rise up, then fall back down. If so, you're golden.

What's the small screw (#1) for ?   It's near the rear of the carb, right at the manifold.  I figured it was a vacuum port ?  No ?

[tbpmusic]

Mine have what I assumed was a port for synching.  At the diagram, it doesn't have the part for the screw listed, but it does for the washer.  (part #1)
I wonder if I were to add light spring to them?     These are shockingly clean though.   I guess I like a positive snap to the throttle.

There's no vacuum port on a 450 carb.
Adding a spring would most likely screw things up.
Take a soda straw and blow into one of the holes around the carb intake opening - the side should easily rise up, then fall back down. If so, you're golden.

What's the small screw (#1) for ?   It's near the rear of the carb, right at the manifold.  I figured it was a vacuum port ?  No ?

I think you are talking about a little plug that covers a hole used to cross-bore in the carb body.
There's about a dozen #1's in your diagram.........

[jays100]

I personally like the labyrinth seals on the non-diaphragm types.  more expensive to make but they're the more precision device and quite sensitive to differences in air pressure - the whole idea of a CV carb.