Vacum Advance

[pugit666 2]

i've read as many topics as i could find on this but would like to know what to do with the vac advance outlet on the dizzy.

 

I'm running an mi16 on bike carbs, do i leave the pipe open to atmosphere, blank it off or connect it to something and if so where?

 

thanks for your help in advance

[Anthony 1,003]

The vacuum takeoff on the carb/manifold, assuming there is one, otherwise it would be easy enough to drill and tap a suitable takeoff - just make sure that it's on the engine side of the throttle plates so that the dizzy will "see" vacuum under idle and part-throttle.

[unariciflocos 49 1 Cars]

As Anthony said you should connect to what it was supposed to be connected to. Without that advance you'll lose power in the upper rev range. Make sure the vacuum capsule isn't broken, just suck on it and see if there's resistance. If so it's fine, if not it needs changing.

 

(Did you sort your reving issue?)

Edited February 26, 2009 by unariciflocos

[pugit666 2]

great stuff thanks for that, i'm just learning as i go so all your help is appreciated.

 

i haven't sorted the revving problem yet, going to play with the dizzy today and see what happens, i put bigger jets in a couple of days ago which seemed to help.

[pugit666 2]

thanks for your help on this one, the vacuum pipe has made a huge difference. She revs right round now. just need the fueling setting up properly .

[bales 1]

Without that advance you'll lose power in the upper rev range.

 

That is actually wrong though, you won't lose power in the slightest, if you had your foot down there would be no vaccum to act on the dizzy anyway.

 

It is there as a basic method to improve part load fuel economy, you would only see a vacuum if you were on idle or part throttle.

 

I have run about with them diconnected and connected and tbh I have never seen any meaningful improvements to fuel economy, but then again that could be due to driving style.....

[unariciflocos 49 1 Cars]

You're right about the vacuum at WOT, but I still say you need the vacuum advance for the driveability and my opinion is that you're losing power if not in the high range then in the low to medium.

 

Even when driving really hard you won't be running wot at all times, at least from my experience that is an inefficient driving technique. You need partial throttle to keep the revs in the max torque range from standstill, you need to squeeze on the power when accelerating or pulling out of a corner to avoid wheelspin (I know it's fun, but that doesn't make it efficient lap-time wise). If not for this the throttle would have just been an ON/OFF switch.

 

In conclusion you need a proper advance curve all through the rev range and i think the vacuum helps.

 

I used to run a vacuum tank on my 8v because of the lumpy cam.

Edited March 5, 2009 by unariciflocos

[Tedglenn 1]

Dear All, before I go making a connection can you tell me where on a standard car the vacuum advance fits to the manifold ? I have a standard manifold but a K&N set up. Not sure where to put the pipe from the dizzy. Thanks Ian.

[stefan 4]

On the throttle body, on the underside.

[welshpug 1,661]

on the bottom of the throttle body there will be a small (circa 3mm) takeoff to fit the pipe onto.

[Tedglenn 1]

Thanks guys found it...what a dummy..i somehow convinced myself it was on the manifold. Cheers Ian.