8 replies to this topic

[mtbtimr]

Just got some twin SU carbs for my Austin 1300. They don't have a nipple to plug in the vacuum advance to the distributor. 

 

They do have a large vacuum port on each carb (currently joined with a Y connector). 

 

Do I have to make up some kind of adapter to connect the small vacuum advance hose to the large vacuum ports? 

 

Cheers. 

 

Pics for interest. 

 

 

 

 

 

 

[timmy850]

Cooper S twin carbs didn't have vacuum advance. 

 

The vacuum port on the sides is normally for the emissions control, and might not be on the correct side of the throttle to provide a vacuum advance signal.

 

You can:

Ditch the vacuum advance

Get another carb with a vacuum signal (the early Cooper had it coming from one side)

[Spider]

They sound like late Cooper S Carbs, fitted with CCV (as opposed to PVC). They didn't have the vac advance port.

 

Cooper sets did.

 

While it's a good idea to connect the vac advance if everythings there for it, I wouldn't loose sleep if you can't.

 

With regards to the CCV Ports, they connected to a Y piece

 

https://www.minispar...|Back to search

 

and then to the crankcase breather.

[gazza82]

You could replace one of the spacers between carb and inlet with one that has a vacuum take-off .. http://www.minispare...s/Fittings.aspx

[timmy850]

You could replace one of the spacers between carb and inlet with one that has a vacuum take-off .. http://www.minispare...s/Fittings.aspx

Those spacers are on the wrong side of the throttle to give a true vacuum advance signal, at idle it will give a vacuum signal.

On the other side of the throttle there is no vacuum at idle.

[Spider]

This is how the CCV Ports should be connected;-

 

 

 

You could replace one of the spacers between carb and inlet with one that has a vacuum take-off .. http://www.minispare...s/Fittings.aspx

 

Not necessarily a good idea as the Vacuum is not controlled. In the HS type Carbs (and most others), the Vacuum take off for Vacuum Advance lines up with the Butterfly such that at Idle, there is next to no Vacuum for the Advance. This reduces the likelyhood of overheating while waiting at Traffic Lights and the like.

 

I know most of the HIF series have the Vac always present, but I re-drill them for the same reasons.

 

<Edit: Timmy beat me to it again!>

Edited by Moke Spider, 08 July 2016 - 08:10 AM.

[gazza82]

Stand corrected ...

[mtbtimr]

Thanks all for the advice! 

 

What are the consequences of not having a vacuum advance? Why didn't the Cooper S have one? 

[carbon]

No vacuum advance = retarded ignition at part throttle = use a lot more fuel

 

Cooper S did not have vacuum advance as you were expected to drive everywhere on full throttle...