Having fun with my SU H6's Basic Question

[Tinkerman]

Been a long time since I did anything with a pair of SU's so I have some basic questions:
1. When the car is at rest, are the butterfly valves supposed to be closed or open?
2. If they are open then pulling the choke will close them partially to allow the car to start?
3. Once the car is running the butterfly's are in what position?
As I read this I'm getting more and more confused,The SU manual did not help me on this basic stuff, so I need some help!

Thanks, Tinkerman

 

[EV2239]

On H6s the butterflies should be open a tiny amount to allow tickover, when you pull the choke out it lowers the main jets by about 3/16-1/4" and opens th butterflies a tiny bit more.

Lowering the main jets makes the mixture rich, ie more petrol for a given amount of air.

The dashpots should be right down to start and they get lifted by vacuum in the inlet manifold as engine revs increase. As you press the accelerator pedal so the butterflies open more and increase the vacuum in the manifold, which pulls up the dashpots and the needles out of the jet increasing petrol flow to match air flow. Clever stuff and SU stands for Skinner Union because the originals had leather bellows.

I hope this makes sense.

Ash

 

[tinman58]

We are all awaiting for the start up Dick!!

 

[EV2239]

The important settings on H6s are:

1. Take lids off float chambers invert them and a 7/16" drill shank should just slide under forks.

2. Make sure floats don't have fuel in them.

3. Set main jets 35-38 thou down from jet bridge. Shoulder of needles should be flush with face of Dashpot.

4. Make sure with tickover screws backed off that butterflies are carefully matched by sliding a 1.5 thou feel gauge under each of them. The same effort should be required to pull it out from under either.

5. Make sure when you attach the choke linkage that the main jets are still 35-38 thou down.

This is how they were set by the factory and the cars ran perfectly once tickover speed was adjusted. Nothing else was needed.

Ash

 

[poolboy]

"Skinner"..I thought that was a family name. Of course back olden times England that doesn't rule out the family being in the slaughter house or tanning business

 

[EV2239]

"Skinner"..I thought that was a family name. Of course back olden times England that doesn't rule out the family being in the slaughter house or tanning business

I believe they were.

Ash

 

[martx-5]

"Skinner"..I thought that was a family name...

Skinner is the family name. The carb was designed by George Herbert Skinner in 1905... more info here.