I've found a single Dellorto 40 with manifold extractors etc. is there going to be a worthwhile performance gain without costing too much extra in gas, that's what put me off the twin 40 set up, my mates B310 A15 used $80 of gas between chch and nelson, my car uses $35 fully loaded and my mates 2JGTTZE 2.5 litre Twin turbo 1700kg supra only uses about $60 worth !

Hey Will, i would check out the shape of the ports on the manifold.....All of the single weber manifolds i have come across over the years have been for round port heads. Which wouldn't be suitable for the GX or A14/A15 type head.
But if you have the standard head.....it would be great.
I seriously doubt that you would retain the economy of the standard carb, if you were to use the weber/dellorto setup. On the other hand, you would feel a reasonable increase in power....also the engine should also breathe better.

Cheers

Hey Will Im the one selling the Carb, is for a std 1200 head, i brought it when I was expecting to work a 1200 but now that I have got an A15 is no use to me.

If the carb is properly tuned for driveability/economy, you'll get close the original fuel economy, unless you are driving faster

Many performance carb setups aren't tuned, or are tuned for maximum performance (like 12-13:1 fuel ratio), rather than for emissions (14.7:1) or for economy (lean) as is the case with the stock Hitachi.

In other words, tune that sidedraft carefully, and you'll get good fuel economy out of it. And when you put your foot down and hold it, it'll still give better performance than the stock Hitachi ... my disclaimer is I've only tuned Holley 4-bbls and Weber 32/36, but reportedly the Weber and Dellorto sidedrafts are fully tuneable in the same/similar ways, and the air cleaners don't even have to be removed to tune them making them easier to rejet than the 32/36.