May be a really dumb questions, however what are the pro's and con's of the 2 kinds of carbies?

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It's not the size of the dog in the fight, but the size of the fight in the dog!!

1976 Mini SS
1971 Mini Ute (Custom) - really hubby's but I will claim half
1976 Mini SS Shell
Oh and an 850 shell waiting for our dear son to start his resto!

SU:
Pros-
Good economy. Can provide vacuum advance to dizzy.
Quieter.
Good emissions.
Good low speed and midrange torque.

Cons-
Getting the right needle selected, there are something like 800 now.
Throttle shafts wear eventually (on HS series) and give air leaks.
Needles rub on the jet (floating needle types)- can wear both badly in 20,000km.
Harder to tune, ie not many dyno places speak SU.
With twin setups, linkage can wear, putting them out of balance with each other.

Weber DCOE or Dellorto DHLA:
Pros-
Better top end power (usually).
The NOISE.
Once tuned they stay tuned. Both barrels are synchronised on a single shaft.
Throttle shaft has ball bearings and seals.
Better throttle response over 3000rpm.
Very tuneable, heaps of jets etc available.

Cons-
Poorer fuel economy.
Poor emissions.
Bad choice for a city driver, due to poor low speed throttle response.
Difficult to fit into a Mini on a decent manifold (for high power) without cutting firewall.

You pays your $$$, and makes your choice.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks!

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It's not the size of the dog in the fight, but the size of the fight in the dog!!

1976 Mini SS
1971 Mini Ute (Custom) - really hubby's but I will claim half
1976 Mini SS Shell
Oh and an 850 shell waiting for our dear son to start his resto!

Just thinking aloud again , would it be possible to make a single shaft for twin SU's , I know it would involve a lot of fiddling to make sure both carbs were set up in line but it could help in tuning ????

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It would be possible but thermal expansion and other things would affect it. The Stock BMC way works as long as the operator knows what he is doing when he sets it up.
The Warneford way with the W clip that was fitted to the Sports 850 and the BMC Hot Up Kits is probably a good enough solution.

Anything is possible. The problem with 1 shaft and 2 carb bodies is synchronising the idle, I would say.
Early twin setups like your 850 Sport had 1 shaft. OK, so it was 3 bits joined by W-clips..
The Cooper & S 3 piece shaft setup is OK and works well with all new bits, unfortunately the bits do wear with time.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

go the weber, love the noise and there is also the noise
cheers

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busier than a 0ne legged man in a butt kicking competion

and what about that noise?!

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Starlet Conversion:
http://www.ausmini.com/forums/viewtopic.php?t=15484

As you can probably guess, Doc is a Weber fan

I'm impressed by the design of the SU, it dates back to the early 1900's and hasn't changed much in that time because it works so well. There are shortcomings as Doc described, but IMHO they're outweighed by the ability for the average owner-mechanic to understand how the thing works set up for their car. It usually takes dyno time to get a Weber properly dialled in, and while it can benefit an SU too, generally you can get by without.

On the other hand, I can't for the life of me figure out the HS4 on my clubby van.. so there's two sides to the story

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Simon

The adventures of an owner builder in the Tallarook Ranges