Timing question

[splod77]

Hi I've just fitted a powerspark dizzy with the electronic module fitted.
What should I set the timing to? 30 degrees with vac line plugged?
If this is the case should I get more advance when I reconnect the vac line?
Thanks for any help Paul

 

[bac2ba6]

As far as I'm aware you set the same as points. So 28/32 degrees at approx 3000 to 3500 rpm with it settleing around the 7.5 Mark on idle . But I've found anywhere between about 5 and 10 degrees on idle is ok it's the max advance that's important . And yes when you stamp on the loud pedal it will advance briefly above the 30 mark for a svda dizzy
And yes plug any vac lines while setting up .
Someone with a bit more in-depth knowledge may have a better description .


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[StefansBus]

Yes, points or no points, the timing stays the same. The correct value depends on the distributor and requires a correct(!) vacuum signal if it's not a centrifugal advance only dizzy. What engine are we talking about? The B-Code engine (1600 single port) came with a vacuum only (not a SVDA) distributor which is set to 0 degrees TDC with the vacuum line disconnected. The 1600 twin port (or dual port) engines are usually set to 7.5 degrees before TDC with the vacuum line in place. Yes, it is always a good idea to also check total advance if possible.

 

[splod77]

It's the 1600 twin port
I plugged the vac lines when checking max advance and set it to 30 degrees and it was 7.5 on tick over but when I reconnect the vac line it still ticks over at 7.5 but the max advance is quite a bit past the 30 degree mark when it settles.
Is this correct? Surely it should still settle around the 30 degree mark?

 

[Raggles]

As I understand things - on the SVDA dizzy which takes its vacuum signal from the manifold, the vacuum advance will have little impact at idle when left connected as the vacuum signal is small - however you should still time with vacuum disconnected and plugged as it will have some impact. This is because despite the throttle being barely open when the revs are at idle the manifold vacuum will be very low.

However, when the throttle is opened a little further and the engine is under little or no load, the revs will rise quickly and then the vacuum signal will also increase advancing the ignition. So at higher revs with no load on the engine the engine will advance further than the 30 degree mark because you have the vacuum advance added to the max centrifugal advance - this is the condition when you time the engine without a rolling road and why you disconnect and plug the vacuum (advance beyond 30 degrees via the dual advance without significant load on the engine is in line with the dizzy design and is fine). When the throttle is opened further to respond to more load then the vacuum signal reduces because the vacuum itself drops in the manifold ( the carb plate is wider open and sucking in more fuel) - therefore the timing advance automatically drops back in direct proportion to the increasing fuel richness. Under significant loading at 3000rpm the vacuum signal will have gone entirely with the mechanical advance only now setting the advance to the timed 30 degrees.

The benefit of this is that the advance reacts not simply to the revs but also to the richness of the fuel mixture and therefore the loading on the engine.

You don't want the engine timed beyond 30 degrees under any significant load as it will detonate - hence you ignore vacuum advance when timing by disconnecting and plugging the port. The engine can cope with more advance under light loads and this improves fuel economy and emissions. The SVDA was designed to run in this way and is fine.

This is my understanding anyway ... hope its right!

 

[atafonso]

Max advance WITH vaccum connected should be around 30-32 deg. You will find that at idle it can be anywhere between 0-10deg sometimes depe di g on the distributor. As long as you measure max of 32 with all connected you should be fine.
Abel