Vacum Advance & Timing

[Guest Ken Brough]

Can anyone give me any advice on the following items please.

 

Q1 Do you require a vacuum advance connection when using twin 40s and a distributer with vacuum advance.

 

If so where about on the manifold do you take the connection.

 

At present there is 1 raised, drilled and tapped hole on cylnder no 4 which i presume is used for the brake servo and one raised non drilled on clynder no1.

 

I took some photos at Donnington last year under the odd bonnet or 2.

 

I can just about see on one picture what looks like 4 connections into the manifold, then teed together back to the distributer.

 

Q2

 

I am currently using a 2.1 pinto. It will start off the key when the ignition timing is set advanced within 1 mm of tdc however is does not rev very good.

Once running the distribiter can be advanced approx 5mm away from tdc and the engine will rev and drive perfect. However once switched off it wont start up in the same position.

 

I am getting my hands on a strobe light next week does anyone know the best setting bearing in mind there is a big cam fitted (Dont know exactly which one) and a vernier pulley.

 

Q3

I cant get petrol to run to the carbs when i fit the pressure regulator. The fuel runs fine when i by pass the valve.

 

Does the return pipe require some type of non return valve or should i just use the other connection on the fuel sender as a vent.

[Guest Tim Norman]

In answer to nr 3 are you fitting the valve the right way round?

 

Nr 1 I wouldnt bother with the vaccum advance, and it sounds like the cam timing is out. Find a standard cam wheel, set the cam right. Try setting the static timing at about 10-12 deg. The put the vernier back on.

[Guest Ken Brough]

Thanks for that one tim

 

as for the regulator valve there are a couple of arrows on it

 

i have the small one running back to the tank the large centre one to the carb and the large outside one from the tank supply

[IanS]

The thing to remember is that the vacume advance is there for economy. It comes into its own at part throttle.

Tapping into just one cylinder, especially with a large overlap cam, gives a lot of presure pulses to the diaphragm on the distributor and so the advance does very little except cause the diaphragm to flutter. Trying to connect all 4 together helps a bit but you do not get the full vacume so you only get a small improvement in mpg.

 

Expect 20mpg with no vacume and posibly 25 - 27 with all 4 connected.

[Guest Bazwaz]

I remember a thread about this on the old discussion board (is it still accessible?) posted by Simon Cooper. If i remember correctly when you tap into the manifold you are on the wrong side of the carb butterfly (you should be on the atmospheric side) and therfore getting full vacumn straight away. You should be aiming for something like (if i remember) 28 degrees @ 3500 rpm. Hopefully Simon's reading this and will correct me if i'm wrong. Anyhow you could always e-mail him for advise as he his an engine tuner and a very obliging chap.

Barry.

[Guest Wozzer]

Hi All,

 

I am converting EFI to carb.........the engine has a distributor without a vacuum advance on it. I was going to change it for one that had this advance !

 

Do I not need too?

 

This has me totally confused as my manifold has a take off on port 1 (twin 40's). Reading some literature on this subject the take off should be at the butterfly valve on the entrance to the carb........

 

Do I need a new dizzy or keep the existing without vacuum and seal off the take off hole on the manifold?

 

Wozzer

[Guest Bazwaz]

The single take off could be for the brake servo (if you have one)

Barry.

[Jez Morton]

Hello,

I have basically the same setup, I'm using the Sierra fuel regulator as standard with return. I have connected the rear take off to the servo and the front to vacumn advance. With one port connected to the vacumn the dizzy rattled as the vacumn pulsed so I fitted one of the none returns that was on the Doner that solved the pulsing.

[Guest Charles B]

Wozzer, you can't use the injection dizzi by itself, as it has no mechanical advance. You need a standard type, and lock off the vacuum advance. Aldon or Burtons do a dizzi with no vacuum, and the mechanical curve set up for webwers, but they are expensive.

[Guest Bazwaz]

And they also have contact breaker points in them.

Barry

[Longboarder]

Jez, air is supposed to flow to and fro in the vacuum tube depending on manifold vacuum. A non return valve nullifies this and there won't be any advantage.

The easiest/cheapest setup to get is an inductive discharge unit, bosch dizzy and coil from an 85 or earlier 2L carb model or 1.6 but not the economy 1.6. The dizzy has a vacuum unit but don't connect it. Pic below.

 

Nigel

[Jez Morton]

Longboarder, your right I didn't fit an NRV it was one the fuel traps fitted in the original vacumn advance system I used it to act like a buffer and stop the dizzy pulsing. My system is exactly as per your photo and works fine, whether the vac advance works doesnt really matter I needed to plug the pipe anyway.