Vacuum Advance

[Guest Larson250]

Hi,

 

Just had a couple of guys around to set up the timing and balance the bike carbs on my zero. The timing man says that I need to use the vacuum advance pipe from the dizzy to the manifold or I will get a flat spot in the rev range.

 

I'm sure I have read on here that I do not need to use it.

 

Any thoughts?

 

It's a 2.0 pinto with ZX6R carbs on a GBS manifold. The manifold has a take off pipe on cylinder 4 but this would have to be drilled through.

 

Regards,

 

Dean

[Guest woolly]

can't use just one take of for the vacuum as it will pulse to much. so best not used.

so you can only set best average set for most conditions.

 

 

woolly

[Guest SEgan]

Vac advance has little to do with performance as it is not operational at WOT. Improves ‘cruising’ economy and part throttle response, so unless you are bothered about saving a bit of fuel don’t bother.

 

Being a tight bloke from Yorkshire I “bothered” with my bike carb set-up.

 

I took vac signals from two inlets and combined them in a small plenum chamber to smooth out vacuum. Works fine except there at idle there is full vacuum as it is not a ported signal therefore you get a little too much advance at tickover.

 

Chamber shown by the blue arrow in the picture below.

 

Sean

 

[agent_zed]

can i assume you are also able to attach the servo to the plenum? as i guess you would have to run a non-servo assisted brake setup otherwise. which would be another reason for adding it if iam correct in my thinking.

[Guest Larson250]

Hi again,

 

There is no servo for the brakes on a Zero so I think I will see how it goes, and if it becomes a problem then I will look at Sean's idea.

 

Thanks for the replies,

 

Dean

[Guest salty_monk]

Made a difference of about 5mpg (having the vac advance increased MPG) on the two cars I had with same spec engine & carb. There are also some other benefits to driveability for a road car.

 

Dan

[Guest kj7]

Made a difference of about 5mpg (having the vac advance increased MPG) on the two cars I had with same spec engine & carb. There are also some other benefits to driveability for a road car.

 

Dan

 

 

What dizzy are you using? if its from a 1.6 pinto these are good for a set up with bike carbs as i spoke to H&H about the subject and what he said was set it up about 10deg btdc and take it out and listern for it pinking and if does adjust it to suit.

If yoou like they can remove the vac mech from your dizzy and re curve it for you.

I dont think that 4 pipes into a small cylinder would work as it would not smoth it out, a few people have discussed this on the locost site, if you do a search on the subject.

[Grizzly]

Made a difference of about 5mpg (having the vac advance increased MPG) on the two cars I had with same spec engine & carb. There are also some other benefits to driveability for a road car.

 

Dan

 

Ah Ha! That may well explain why my MPG isn't particularly great then?

I had my vac pipe disconnected when I took the car to Bogg Bros

Dave said the Dizzy was worn and was giving too much Advance with it connected.

He said that the Bob Weights alone would provide enough Advance and so we left it at that.

Hmm - Maybe I need to look into getting my Dizzy reconditioned and bring the Vac Advance back into play?

[Guest MrT]

hi

 

I have the same GBS bike carbs as you and dont have the VAC, but I did change the distributor for a Besteck set up which is excellant , no issues all through the rev range and loads

 

Paul

[Guest Larson250]

Thanks guys,

 

I have got my IVA test next week so I will hopefully soon be able to do a few test runs etc.

 

Reagrds,

 

Dean