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erstearns
03-08-2009, 07:16 PM
Was perusing the thread for the velocity stacks and it got me to thinking about carbs for my BE. The 1275 I acquired for the rebuild,now 1310 I think and mated to a Datsun 5 speed, came with a single SU from the PO. The throat is 1 3/8". PO told me it was an HS2 but seems too big...........came off of an Austin American (?).

In any event seems like I have some carb and manifold work to do. Any suggestions?

Bayless
03-08-2009, 08:40 PM
Right, the HS2 is 1-1/4 and a 1275 uses 2 of them. That gives a total area of 2.45 sq in. The single carb you have only gives 1.48. That's not gonna be enough for the 1275.

erstearns
03-08-2009, 09:16 PM
I agree that the surface area is quite small. Given that, I have a variety of choices, install typical HS2's, install twin of whatever I have (too small for HS4, did they make a 3?), go with a single Weber or whatever options are out there. What to do?

Sarastro
03-08-2009, 09:51 PM
If you plan to have a stock engine, and have no good reason to do otherwise, it seems that reverting to a stock HS2 configuration is the thing to do. You can get a rebuildable pair plus manifold and heat shield fairly cheaply on ebay, you know it will be right for the engine, and all in all, minimum hassle.

If it's not going to be stock, then what you pick depends on what your intentions for the engine are. Let us know, and I'm sure there will be plenty of opinions!

Hairyone
03-09-2009, 07:46 AM
I'm about to replace my twin 1 1/4" SU for one HIF44 on my 1275 in my bugeye. Reading other measages I believe it's the way to go, and better torque and economy over a webber. Webbers out perform SU's at higher revs.
That's what I've read anyway.

Gundy
03-09-2009, 07:47 AM
My BE came with a single carb as well. It's a HIF6 SU.
Car runs sweet but I too am wondering if a twin carb set up
would be an improvement.

nomad
03-09-2009, 08:35 AM
If you read David Vizard book on the A serie's engine you will find that the single SU carb route is probably the best. He's sort of the guru on the subject.
KA

Gundy
03-09-2009, 08:47 AM
If you read David Vizard book on the A serie's engine you will find that the single SU carb route is probably the best. He's sort of the guru on the subject.
KA

I would certainly defer to a guru. I haven't read his book but I'll seek it out now. Thanks!

Sarastro
03-09-2009, 10:59 AM
Yes, he suggests a single HIF6 SU, but that's because he considers the HIFs superior, in performance applications, not that a single is preferable to a dual (pages 74-75). Note that you need an HIF6 to have the same throat area as two HS2s.

As soon as you deviate from the original setup, you have to start worrying about tuning--getting the right needles and so on. If you are modifying other aspects of the engine, you might have to do this anyway, but it seems like wasted effort if the engine is stock and used in ordinary types of driving. So, back to my original question: what is the goal of the engine rebuild? Just a new, working, stock engine or something hotter?

nomad
03-09-2009, 11:24 AM
I don't disagree with you, Steve, but if he has a single manifold already it seems as if digging up a HS 6 or HIF6 would be the way to go. If engine is modified there will be carb tuning issues anyway. I haven't gone this route but I think it would be easier to tune just one. Also, I would have to go back and reread Vizard, but it seems as if flow in the correct single manifold was better than stock dual's. So or not?
KA.

erstearns
03-09-2009, 11:26 AM
The single carb that was installed is a SU with a throat diameter of 1 3/8". Anyone have an idea what it is? PO said it came from an Austin America?

erstearns
03-09-2009, 11:29 AM
The 1275 I have acquired is aboaut 1310 now and has a mild Kent cam in it. It is mated to a Datsun 5 speed. I have a single manifold but it is not problem to go another route if that makes sense. I would like to squeeze all the performance that I can within reason (can you say that when you have 3 cars in the rebuild stage?).

nomad
03-09-2009, 11:51 AM
Eric: In hind site I would suggest you read Vizard and decide for yourself. Dual carb setups are common and I imagine someone would definetly be interested in your single manifold. Carb size? can't guess, unless its been modified for some reason.
KA

erstearns
03-09-2009, 06:08 PM
Eric: In hind site I would suggest you read Vizard and decide for yourself.

Good advice. Will do. Have plenty of time. Thanks

Hap Waldrop
03-10-2009, 07:49 AM
Nothing worng with a single carb, I might argue the HIF being a better carb than the HS for all-out performance, you won't see many at the race track. The twim HS2 set up work good for almost all 1275 street applications, and most of you already have that, so it easy to run with. Vizard is smart but a bit dated, tell him to call me when he can make 120 HP with unported head, stock HS2 carbs, 11.0 to 1 compression, stock rocker arms, and .450 valve lift, good book, oh yeah, up to date, no way.

erstearns
03-10-2009, 08:40 PM
Hap, given that I dont have any HS2's, nor any manifold for same (only pile of 948 HS1's and a single HS4), what would you recommend I look for? Tried and tru HS2's or find a mate for the HS4 I have (i think that is what it is)and a dual mainifold??