Well ive finnaly decided, yes, im going to use quad motorbike carbys on my A15 build for the 1000 wagon!
Ive read every discussion on here that i can find about it so dont go telling me to search

I went to a bike wreckers the other day and the guy said i would be looking at AUD$300 for some quads and knew what i was after! Other poeople on m/bike forums have said $200-$250.

Going from research and from people ive asked 35mm-40mm seems to be the go. The A15 they will be going on wont be a power hungry monster either, just a mildly worked A15.

Im also planning a airbox with a pod filter just behind the front grill and ram tubes on the carbys!

What i still need to know!

-Would I have any drawbacks in making a steel manifold opposing a alloy one. steel will be much easyer(welding etc) and cheaper!
-What runner length am i looking at? I think there is a website for this?
-To i have to run a balance tube like in duel SU manifolds?
-Can i tap my dizzy vac adveance line in anywhere(not running a booster)
-Wil the standard mech fuel pump be enough? Ive heard bikes run at 3~4psi

I'll be updating this thread with progress so stay tuned!

Thanks in advance!

first are the carbys vac opperated or cable .Ive seen the cable set up >they dont run a balance tube .you will also have make fuel rail with adecent diametre tube as the M/bike fuel bowl are tinny .....Id also look for a mechanical advance/retard dizzy set up would be the go .sounds like alot of fun should go well ..........

just remember that if you go for a 35mm\40mm the engine may loose low end responce (dellortos and webers say thay are 45\40 mil but the chokes are 30mm\23mm, For an a15 i wouldnt go past 34mm opening
or you may loose snap and out of corner pull

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.

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?

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

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...

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..."

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.

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.