Why no vacuum advance

[rfurzer]

How come?

[AHM]

Maybe because it is Vacuum retard?

[rfurzer]

Hey Man! I'm no retard!

There is no vacuum change to the timing - never come across that on any prev car i've owned. Why did they do it this way?

[rgh0]

Vacuum advance is there to help deliver part throttle fuel effiicency. This was not a high priority for Lotus back in te 60's. Also there is substantial problems getting it to work with Webers and the mechanical advance systems avaiable in the 60's and that would have added cost and complexity it they actually wanted to do it and cost and complexity is something Colin Chapman hated!

cheers
Rohan

[andyelan]

Hi Everyone

Late model UK and European Twin Cam engines did in fact have distributors with vacume capsuals. Presumably this was necessary due to the strictor emission regulations which were comming into force around this time

Andy

[alan.barker]

my august 1973 +2s/130 has no vacuum capsule
Alan B

[Tonyw]

You can have vacuum advance and vacuum retard, it depends on where the vacuum port is within the carbs, usually the port has progressive vacuum where on light throttle and beyond it progressivly get more vacuum the vacuum advance allows the timing to advance aiding better fuel economy, plant your foot and the vacuum dissapears as will the advance so no pinging, vacuum retard usually has full vacuum at low load, idle cruise so when you plant your foot the vacuum is lost and the timing is retarded with this type you need vacuum to the advance unit as you time the car up at idle.

Tonyw

[quaybook]

To the best of my knowledge cars of the period with single choke per cylinder carburation did not have vacuum advance. I believe this was because with this set up vacuum could only be drawn from the inlet tract to a single cylinder, and at low engine speeds (idle) the vacuum pulse of a single cylinder caused the advance mechanism to 'flutter' - not good for the mechanism or for smooth running. If you tap more than one inlet tract for vacuum, you upset carb balance.

Vernon

[andyelan]

Hi Everyone

The distributor I'm talking about is the 25D4 41225A fitted to Plus 2s and Europas after November '73 as part of the ECE15 requirement

In operation, with a closed throttle, the vacume retards the ignition timing by pulling against a spring. When the throttle is opened and the vacume lost, then the spring advance the ignition (not sure if this should be described as a vacume advance or retard). If you look in the workshop manule for the timing for this distributor you'll see it quotes 10 degress advance static but 5 degrees at idle, the 5 degrees difference being the effect of the vacume retard

To be honest I've run my Europa both with and without the vacume capsule connected and I couldn't tell the slightest difference

Andy

[RogerFrench]

Federal Twin Cam engines in Plus 2s and Europas (US market) have vacuum retard distributors as standard.

[simonknee]

"To go faster, just add lightness"

(actually I second what quaybook said - there was a discussion last year about the 123tune dizzy that had debate on vacuum advance and webers)