Pinto distributor

[Ross (Rosshbar)]

Fitted new distributor, but the one I fitted has vacuum advance , previous distributor didn't and doesn't connect to my twin Webber carbs . Should I

1. Remove the vacuum mechanism not what I really want to do as timing all now nicely set up

2. Cap the vacuum outlet

3. Leave vacuum outlet open

Ross

[Ross (Rosshbar)]

Sorry should have put this under tech doh!

[mikef]

My distributor has a vacuum fitting but is not connected.  The vacuum outlet is just left open and the engine runs fine.

[Martyn Vann - Warwickshire AO]

It is not a problem to leave the vacuum advance disconnected and uncapped as is often not used on an engine that has been tuned and/or had twin choke carbs fitted.

 

However, a performance distributor will not have any vacuum advance facility at all but the mechanical advance is different to a standard distributor so this may have some consequences if you have changed from a performance type to a standard type? 

[Welly Jen]

As has been said, the usual practice with twin DCOE carburettors is to leave the vacuum port on the distributor disconnected. To connect it you would need ports in all four inlet manifold ducts. The vacuum signal would be very lumpy at tick over, due to the low overall volume of the inlet compared with the manifold for a single carb that the distributor was designed for. Even if the vacuum was connected a standard distributor may not give the best advance at all combinations of engine speed and load if the engine has been modified with go-faster bits.

 

The problem is that the vacuum alters the timing on the distributor depending on the load on the engine. Low load will give low pressure (more vacuum). Opening the throttle will raise the pressure. Without this connection the distributor will only alter the timing based on engine speed, not engine speed and load. Distributors for modified engines often have the springs changed inside to alter the timing rotation with speed and yours may not have this if it has a standard distributor. The timing will still be a compromise, so over some parts of the speed/load space it won't be optimum. On my Pinto car this lead to a dead spot around 3000rpm and partial throttle for example. On a road car where you are not always driving everywhere at full throttle this can be a bit annoying.

 

I changed the ignition to mapped 3D using a Megajolt ECU, a crank speed sensor for engine speed and a throttle position sensor on the Weber DCOE's for engine load. This was one of the best two upgrades I've done on the car. The other was a gearbox with better ratios. It eliminated the dead spots and the engine started more easily and pulled well throughout the rev and load range. There are other ignition only programmable ECU's around like Nodiz.

 

Jen

[Lawrie]

Like the power tune carburettor bible, there is also one on distributors.

 

From memory, a standard distributor has too much advance, which can be restricted, but my pinto was a pig to start, probably as a result.  However, it does suggest for full power, to set the timing at 4,000 rpm (ie at full mechanical advance), and I think this was 38 degrees which I marked on the pulley.

[Andrew]

I got Bestek to tweak mine. They removed the vacuum advance mechanism, welded up the base plate and adjusted the advance curve to suit my engine tune. Wasn't expensive.. £30 to £40 If I remember.. and a quick service.

 

http://bestekuk.webs.com/

[Ross (Rosshbar)]

Thanks car is runing well will just leave vacuum open at present, maybe something to think about for winter job