Vacuum Advance at idle question

[grantius]

Hey guys,


Since ripping out the EST computer I've been driving around without the vacuum advance attached so I've decided to attach it so I get better fuel economy.

Question - I've hooked up the vacuum advance to intake vacuum as AFAIK there isn't any ported vacuum on the EST carb. Is this the way these dizzy's work? Most advance at max intake vacuum and as vacuum drops the timing is pulled? Or the other way around?

It idles a bit high after connection - around 700rpm when disconnected and close to 1600 RPM when connected - is this normal? From what I've read the extra timing shouldn't rise the idle RPM that much.

And if I now turn the idle screw down so it idles around 700 will that be all I'll need to do tuning wise?

If it is a stock replacement blue motor dizzy I'd think it won't ping when cruising as it's not exactly an aggressive tune. At the moment I can run 91 without issues but if I notice any pinging at light throttle I'll fill up with 98

Thanks

 

[grantius]

so I've been driving it around with the vacuum advance on and the car is much more responsive under part throttle.

For some reason with the vacuum advance connected when starting the engine warm it pops over within half a second, with it disconnected it would take a little bit of cranking to start.

The idle RPM's sitting at around 1600 still remains, when I give it a little throttle the RPM actually drops so I'm wondering if its maybe a little too advanced?

 

[jandjmc]

Yes the car should run a vacuum advance, and it should be ported vacuum not full vacuum. Just a question, why did you remove the EST system. From memory when I was working on them, it was a simple system with most issues relating to the Thottle position Sensor mounted on the carb.

 

[grantius]

Yes the car should run a vacuum advance, and it should be ported vacuum not full vacuum. Just a question, why did you remove the EST system. From memory when I was working on them, it was a simple system with most issues relating to the Thottle position Sensor mounted on the carb.

I removed the EST because it would randomly stall on me, I'd be driving along and it would buck and start backfiring and miss like crazy. I drove it while it was doing it, kept stopping on the motorway and eventually the EST light would come on.

Since swapping it out for the blue HEI dizzy I haven't had a single stall and I've driven close to 500km's since.

Why ported? From what I've read its always better to run manifold vacuum due to a better quality and lower temperature idle. Plus being in NZ the model doesn't have any emissions stuff on the engine so I don't need to pass any tests etc

 

[Silverbird]

From memory on my VK, I installed the HEI dizzy but there was no vacuum port on the EST VarajetII. The car pinged like crazy - ended up putting the EST back in. Had I kept the car, I would have got a VH Carby and run the advance from that.

 

[jandjmc]

The EST system consists of Temp Sensor, Manifold Pressure Sensor, Throttle Position Sensor, ECU, coil, and Engine Speed Sensor. I think the only things that can give you stalling problems are either the ECU or more likley the Engine speed sensor (mounted on the rear of the engine through the bell housing). Other faults usually result in the EST light on and possibly in Limp home. HEI distributor is a good choice also.

As far as the Vacuum advance goes, by using ported vacuum, you get no vacuum advance at idle and when the throttle is opened you get advance faster than the weights react. If you have full advance at idle, you will have quite a fast idle.

 

[Silverbird]

I resoldered my EST computer - never gave another problem.

 

[grantius]

I resoldered my EST computer - never gave another problem.

I'll do that and sell it on.

The EST system consists of Temp Sensor, Manifold Pressure Sensor, Throttle Position Sensor, ECU, coil, and Engine Speed Sensor. I think the only things that can give you stalling problems are either the ECU or more likley the Engine speed sensor (mounted on the rear of the engine through the bell housing). Other faults usually result in the EST light on and possibly in Limp home. HEI distributor is a good choice also.

As far as the Vacuum advance goes, by using ported vacuum, you get no vacuum advance at idle and when the throttle is opened you get advance faster than the weights react. If you have full advance at idle, you will have quite a fast idle.

I would try to force it in limp home mode as when it was in that mode it would be slow but fully stable.

I'll have to change the idle speed screw around to drop the rev's I think, as I don't have any ported vacuum on my car.

Thanks for the help guys

 

[the_boozer]

t the vac advance line into the ported vac line the egr is connected to.

 

[grantius]

t the vac advance line into the ported vac line the egr is connected to.

The NZ models don't have EGR