Well i have the carbies. But im worried they will be too small?!?!

Their 28mm Keihin's off a late '70s CB750.

They cost $350 AUD with a free check over and clean. Manifold is being started on soon. It was gonna be alloy, but it looks like its gonna be steel. all well, ill just paint it!

Also what kind of fuel pump should i run? Bike carbs are gravety fed on a bike. So maybe run a regulator and set it right down low?

Well a little bit of an update. I found a A15, apparently has a cam in it but im not 100% certain. Its never been started since a full rebuild 2yrs ago. It still turns over free as a bird and the bores are rust free and still have the cross hatching on them from the hone tool. So i think its a good one! I may get the head ported and polished(along with the manifold) at a later date.

On the carbies front, I have found a mate of a mate who is going to make me a alloy manifold for cheap! So im starting to look for carbies now. Smaller choke(then what i originally stated) seems to be the go. So ill be looking for 30mm ish. Probably off about a 1200cc bike. Ill see what i can find.

Still donno what to do about vac advance. possibly take it off and play with the centrafugal advance weights? Ill be using my E15 elecy dizzy with the weights right at the very top(uses Mitsu 4G15 cap and rotor so maybe internals are the 4G15 too?).

the formula you are refuring to is rpm x displacement (any given rpm) over 3456 (number of cubic inches in a cubic foot (1728) x2)

but in order to use the formula you would have to know a bit about ignition theory and would only be usful after three or more other formulas are done ie; piston fpm (stroke in inches x rpm over 6) and indicate torque (5252 x horsepower over rpm)

but rather than do that i would just go to a dizzy shop and get them to go 15 at idle (wich with quads would be 1000\1200)
and 35 degrees all in at 3500. it may prove better at 18 at idle but the motor might not start at that

Ok, they use TPS instead of vacuum.
I was wondering.

Is there a formula for that, since a particular throttle position doesn't guarantee a particular vacuum... ( unless you knew the rpm perhaps... )

I'd agree with not getting too big of a choke, it will kill low rpm power. 34 seems plenty big, you said it's just a mild A15 that might be too big even for quads.

"interested in throttle bodies? i think I can get you quad TBs on a manifold for about $250, then just ad fuel only computer, cheap injectors and off you go..."

As already stated...doing this will cause headaches with the vacum advance due to low vacum.
Best bet would be to get a 3D computer...This would allow you to use Throttle position to determine ignition advance rather than relying on a dodgy vacum signal.

Bike T/B's ?

interested in throttle bodies? i think I can get you quad TBs on a manifold for about $250, then just ad fuel only computer, cheap injectors and off you go...

with the runner length it depends on what you are trying to acheive. if you want big hp go with big chokes and short manifold length but if you wont midrange torque go with smallerchokes and longer manifold. i think the best way would be when you design you manifold alow for spacers so you can drive it either way and make your mind up then

suppose you could add ported vacuum, all you need is a place to get a line in right below the throttle plate, if you have any spacers or adaptor plates, that would help.

For the ones that don't have ported vacuum, how do they handle the advance? like the motorbikes, or race cars.

or is vacuum advance sort of a luxury?

The motorcycle carbs, like Webers etc, have no provision for ported vacuum, which is what is required for the distributor. If you draw vacuum for the distributor from the manifold, you will get manifold vacuum at idle to the distributor, when you really want to see none.

Depending on the amount of vacuum, this would mean that you have 100% of the vacuum advance all in at idle when the amount of advance from this source should be zero.

This seems to be the only real disadvantage with these carbs & if you can work your way around it, then you will just love it.