still building car. 1.8 zetec on zzr1100 carbs using esc unit with vacuum advance when i rev the rpm is very slow to come down have 4 vacuum pipes to small chamber to esc if i remove vacuum from esc the revs come down quick .Is this due to the esc keeping the timing to advanced or is it normal with a esc unit ?or carb fault the throttle is closing on all carbs ok and no air leaks .or do i go to nodiz ?

The vacuum pipes need to be blocked off. They are for balancing and also to open a vacuum tap on a bike fuel tank.

This can be caused by a few things but the two common ones are butterflies out of balance or throttle return is not up to the job. Bike carbs usually have two cables with one that snaps them shut when you roll the throttle off. On a car you have one so rely on the return Spring. Not usually a problem but can be. Most likely will need balancing.

vacuum pipes come from manifold not carbs .and have checked balance all ok

Using standard return spring on carbs?

Usually need a stronger spring as above,due to the bike having a twin cable set up

Fit the opposing cable and run that to a big spring to close the throttle.

I found fitting a good spring to the pedal works well then the spring on the carbs is only returning the cable and not the pedal aswell

I had the same issue, and fitted a throttle return spring as per pic below. Just a short bit of cable fitted to the quadrant and some springs and "home made washers" it actually works very well. Since the pic I've added an extra slightly stronger spring.

[img]
Throttle Return Spring [/img]

yes i did think this would fix it but even operating the carb throttle by hand and then holding closed made no difference mmm

mmm found air leak on manifold my poo welding rewelded today refit soon