I read about somewhere (i think it was in this forum) that vacuum advance in properly tuned engine/carburator can improve the fuel efficiency with triples as well. It was somekind of research, cant remember where it was.

Im very close to finishing my project with triple carb setup and i would like to hear about your experience in using vacuum advance with 3 carbs. I have SK carbs and they have vacuum port fitted, though only in one out of 3. Rest are sealed for some reason. Does one barrel provide enough vacuum for distributor?

My engine is stock, with MSA header but i have no-points dizzy. I think timing was set to 17 degrees.

Any info/help would be appreciated.

edit. haha, i had saved the pdf to my dropbox. take a look:

https://www.dropbox.com/s/p0jo85kt4mbbcpe/Weber%20DCOE%20Fuel%20Economy%20Study.pdf

Edited February 11, 201411 yr by Reverend

I'm running distributorless system so I'm out of the picture here but I'm able to control engine load advance with TPS.

At very low load state at steady speed (=max vacuum), my engine is happy with 48°. At 130kph (80mph), I really have to feather the gas pedal to keep the car steady whereas before it would need way more gas pedal travel.

So to the very post, I can say: Yes, you can increase fuel economy by controlling vacuum advance (by 20 to 30%)

When fuel mix is low (low load, low throttle angle), cylinders are not full, gas mix is much slower to burn than at WOT.

2 options exist to get good burn then: you ignite the mix exactly when needed - not possible without load advance control - or you increase the volume of fuel mix. With "poor" (= no load/vacuum control) timing management, you can only use the 2nd solution which is the less efficient.

By controlling load advance, you also improve acceleration/transition. Engine is running in a way more efficient state, transition can be done with efficient mix ("easily" done with DCOE by playing with idle jets) but also efficient advance (going in my case from 48° to 34°). Car is much more responsive as it has ever been when I was running Unilite dizzy without any load control.

here's a very good article about fuel economy, advance load control & DCOE

I'm going to need your timing maps soon for my MS!

Just to kick this topic one more time. Talked with one dude who has MSD box, and he says that static timing (5 degrees) is way too low, and it should be around 15. But that raises the total advance too much (close to 60 degrees) SO i wonder what needs to be done MECHANICALLY to the distributor?

If you can't change springs weights and advance limit stops in your after market then just get the right ZX distributor:

http://www.classiczcars.com/forums/carburetors-s30/51563-vacuum-advance-triples.html#post450025

Check out these posts by Lazeum too...he knows!:

https://www.google.ca/search?q=site%3Aclassiczcars.com+%22Lazeum%22+%22advance%22&oq=site%3Aclassiczcars.com+%22Lazeum%22+%22advance%22&aqs=chrome..69i57j69i58.20335j0j4&sourceid=chrome&espv=210&es_sm=122&ie=UTF-8

Edited March 7, 201410 yr by Blue