VAC advanced dizzy on twin 40's

Not sure if this will get the right response in this section but basically I'm about ready to fit twin 40 Weber dcoe's to my 1.3 polo GT engine which currently is using my golf carb with the vacuum advance dizzy with electronic ignition from early mk2 polo's. This ignition system runs fine but when I come round to fitting my Weber's I'll not be able to use the same vacuum advance. I can't use a vacuum take off from one cylinder because it'll cause pulsation in the dizzy and an erratic idle. Also, running a daisy chain of take offs from the all the cylinders will give no vacuum because the vacuum from one cylinder will be lost into the other three (follows path of least resistance). 

So, in my head, I can only think my options are to run just the dizzy without using the vacuum advance (might cause ignition issues and lack of power and economy) or I could fit the dizzy intended for the polo GT engine which would require purchasing the wiring loom and ECU to go with it or some other standalone ECU system which I would then have to have the vacuum advance programmed into it which seems like they both would be expensive routes (already spent a fair bit getting the required parts so far! ) 

If anyone else has this setup, how did you overcome this issue? And does anyone know how the polo's that were used back in the day for motorsport with this setup managed to do it?

Cheers,
Matt

The vacuum unit can be removed and the vacuum advance plate locked into place within the dizzy. Its then just a centrifugal advance dizzy. However, its unlikely to then have the correct advance curve for use with carbs, fitting the Polo GT electronic ignition ECU will be the same i.e incorrect curve.
The old school way of dealing with this is to have your existing dizzy modified to give a more suitable advance curve. This is quite literally a matter of changing the springs and centrifugal bob weights etc.. luckily there are still some old school tuners out there that can still do it quite cheaply.

I did read somewhere about having the dizzy modified to give a better curve, ill have to look into places that can do that. Maybe even the place that I get it rolling roaded might be able to sort me out. Would it have to be the same place that I get it tuned or can I just send it off somewhere, tell them what set-up im running and theyll give me roughly the right curve?

Cheers,

Matt

non return valves on the ports would help stop u loose the vacuum, maybe a vacuum reservoir would help also?

the kr 16v ecu would work with a polo gt dizzy, but how well i couldnt say

mazza411 said

I did read somewhere about having the dizzy modified to give a better curve, ill have to look into places that can do that. Maybe even the place that I get it rolling roaded might be able to sort me out. Would it have to be the same place that I get it tuned or can I just send it off somewhere, tell them what set-up im running and theyll give me roughly the right curve?

Cheers,

Matt

The ideal would we somewhere that could set it all up on the rolling road..

They'll be able to swing your dizzy for peak horsepower so as to tell you how much your swing needs inceasing, they'll also be able to give you a 'all in' figure, this is the RPM at which the centrifugal mechanism reaches that maximum advance.

For an example, mine was setup with 8 degrees advance at idle and was all in at 36 degrees by 3000 rpm.
It was a stock carb dizzy to start with.

rubjonny said

non return valves on the ports would help stop u loose the vacuum, maybe a vacuum reservoir would help also?

the kr 16v ecu would work with a polo gt dizzy, but how well i couldnt say

I thought about non-return valves but wouldn't that build up vacuum and not release it when vacuum drops? 

I got most if my information off of ford forums but they tried a resavoir and it still had the same effect of vacuum lost into the other cylinders 

addicted said

mazza411 said

I did read somewhere about having the dizzy modified to give a better curve, ill have to look into places that can do that. Maybe even the place that I get it rolling roaded might be able to sort me out. Would it have to be the same place that I get it tuned or can I just send it off somewhere, tell them what set-up im running and theyll give me roughly the right curve?

Cheers,

Matt

The ideal would we somewhere that could set it all up on the rolling road..

They'll be able to swing your dizzy for peak horsepower so as to tell you how much your swing needs inceasing, they'll also be able to give you a 'all in' figure, this is the RPM at which the centrifugal mechanism reaches that maximum advance.

For an example, mine was setup with 8 degrees advance at idle and was all in at 36 degrees by 3000 rpm.
It was a stock carb dizzy to start with.

Yeah that makes sense. okay I'll try to find somewhere that can do my all of this at a reasonable price! What sort of money should I be paying for a RR setup and dizzy modifications do you think? 

Cheers,
Matt

hmm thats true actually... never mind then