I fettled (fiddled) the falt slide carbs before I went to the dyno, it only took about 45 minutes or so to get them dialed in the rest of the way. Most of the issue was because on my A12 the 39mm Keihin carbs are borderline to big for the motor. With the new cam the performance is much better across the range.......................dyno time was $100

This brings up a point about SU style carbs I.E. CV carbs. The Hitachi carbs if they are in halfway decent shape, can be tuned with out swapping parts, as noted they are made for the A series................I wouldn't use real SU carbs personally

Now for some other fun to throw in the mix, Mikuni makes an HSR series flatslide carb which is intended has a replacement for SU carbs. They are a non CV carb so again somewhat less forgiving to being off tune.

The other consideration is using motorcycle CV carbs...................I only used them as a test fit but I did have a set of Yamaha FZR1000 carbs (CV type) on my engine just to see if they would work...........never drove with them but ran the motor..................one could use a set of CV carbs off a big tandem twin...........TDM 850 or old KZ750 twin etc.

Regardless of what you use, anything outside of what was fitted to a similar displacement and state of tune engine will need some fettling...................you can get the motor running decently and then if need be get an expert to final tune them to save a few bucks.

my.02 of course............Tom

Im partial to quad bike carbs, they are light, responsive and dirt cheap. However to setup properly requires some know how.

I think best carb is by far the SUS or hitachi style CV for most people except the higher end hp setups.

Although my manifold will cost a bit of work to setup I think a single SU 2inch 50.8mm is going to be interesting considering Ive been told 50mm can allow more than 200hp.

So is there really bugger all difference between a set of twin SU's and a 32/36 downdraft Weber?

Question being, should I save my pennies for dual twin throats (Weber DCOE/ Dellorto DLHA/ Solex etc...) or get rid of my single Weber and buy a set of SU's to hold me over?

Who said that? The SU-type are better than Weber 32/36. I think nearly everyone will agree.

datsunbeginner, what is your goal? The stock carb is "best" for fuel economy and cost savings -- and reliability (if you buy a new one).

anyone who's used both would agree the 32/36 is better. Twin SU won't give any performance advantage over the single 32/36, and the single carb is easier to tune, less maintenance required, don't suffer from fuel vaporisation caused by radiant heat from headers, which can be a problem idling at lights in Brisbane summers, and certainly for the intended occassional track use.

If he wants a performance upgrade from the 32/26, twin SUs really are a waste of money.

DD - just looking for better performance, more horsepower, faster acceleration, etc. and fairly inexpensive (compared to EFI). I want to keep my A15 carberated but have it go quicker than it is now.

Currently have A15 + 60 series 5 speed + Weber 32/26 + upgraded cam + H165 diff. Extractors/headers to go on soon as well.

I'm not a mechanic but wouldn't the SU's perform better than the 32/36 because the Weber is progressive where as the SU's are not?? Also SU's are sidedraft and the Weber is downdraft - not sure if there is any performance gain there but I have been told so before.

The best throttle performance is progressive. The best full-throttle performance is different. In theory. Some say the non-progressive is better for full-throttle. But it all depends.

SUs are variable venturi so are hard to compare on paper to a fixed-venturi carb.

I was suprised to hear L18_B110 say the 32/36 was considered superior to twin-38mm Hitachis. But he knows more about racing than most of us.

Still, for all-around perf many have said they favor the twin-Hitachis. They work well at low, medium and, high throttle openings.

But why bother? Just go for twin-2bbl sidedrafts. They look great, sound great and work great.

Thanks DD. That's the plan - twin 2bbl sidedrafts. I only brought up the twin SU's as a possibility because someone offered me a pair for what seems like a good price.