I have heard that you can make your own dual carb setup by cutting 2 factory intakes in half, filling the openings, and bolting the to the head backwards (cylinder 1 and 2 flange bolt to #3 and 4 ports, and vice versa). Has anyone tried this???

that sounds very keen!! (lot's of work)

but i have heard of a 1200 with twin downdraughts so it must have been done

if you were going to do that why not just put on a 4 barrel holley?
same effect yes?
way too much fuel?

Yes, yes, and no. Use two manifolds with #1 &2 ports cut off. They don't need to be bolted on upside down or backwards. There's a picture somewheres...

With twin stock Hitachi DCH306, It think you will still be carb-limited on your engine. If each manifold feeds two cylinders, you don't gain much airflow. In other words, one Weber 42 can feed an A12, or twin Weber 40s with about the same top end performance.

A Holley 4-bbl would be too big for an A12. That's like 390 cfm or more. If you don't care about good throttle response or smooth operation of course it would work, or with a drag-racing engine that's run at full throttle only.

or a tractor....
holley's suck.

Here's a pic of homemade dual-downdraft manifold. I think it bolts to a standard sidedraft manifold runners.



dual weber downdrafts

Would I gain any performance from this type of setup or is it just alot of work for nothing? I know it wouldn't be as good as spending the money for the weber, but the cheaper the better in my book.

Yes, you will gain performance. The factory A12 is carb-limited. Changing just the carb to a larger one will give you more performance but only in this situation: extends the torque curve upwards. You can rev the engine a bit higher, subjectively it feels good up to 6000 rpm instead of 5000 rpm.

Might give you a few tenths in the quarter mile? A single weber 32/36 (Ford/Chevy Holley 5200) will wake it up.

In the case of this picture, it is an A15 (25% larger engine than A12) and has an 8500 rpm redline. So it probably has 50% more HP than a stock A12, possibly up to 100% more. Yeah, two carbs is about what it needs! I rode passenger in the car and it screamed, though it didn't launch like a 14-second car. All the power was high up in rpm range, I wonder if you launched at 6000 rpm the car would be fast in a drag race?