I know that when I ask this there are a few variables but I need a starting point. I have Honda Fireblade bike carbs on my Skoda Estelle 1289cc engine in my trials car. I am running a Facet pump into a Filter King filter/regulator and it is set to about 2psi. I am also running an electronic distributor from a Skoda Favorit, a well known mod to do away with the points. At times but not always, when pulling away in first the engine will take time to build up revs even with the foot well planted but at other times it will rev really nicely. Its as if the engine is being choked but doesn't miss fire in any way. Any ideas or any further details required? Could the carbs suffer from fuel vaporization (if that's the correct term) due to heat from the inlet manifold and cause it?

Bike carbs can be quite touchy with their fuel supply and work best with bike fuel pumps. They are low pressure and are self regulating.

My suggestion would be to ditch the facet and fpr and fit a bike pump. It needs to be gravity fed and close to the tank. A simple in line filter could also be used.

I fitted a set of bike carbs and pump to a crossflow a couple of years ago and it's not missed a beat.

My bike carbs played up with facet & regulator until fitted bike pump..

However ..

Make sure your carbs are perfectly balanced..
.. it makes a massive difference

Also.. although my 2.0 will tick over at 500 rpm .. I find closer to 900 rpm tickover gives best off the line no flat spot...

[Edited on 3/10/17 by johnemms]

Looks like it may be worth me sourcing a bike pump. However I cannot position it so it is gravity fed though. Will that matter?

Down next tothe tank is ideal, however before i knew about it I put the zx9r fuel pump on the scuttle next to the engine and it worked fine...

Just get one and try it wherever is best for you.