will a 34 downdraught webber make a noticeble difference in power on an 1108cc uno as opposed to the standard 32?. reason i'm asking is that one of the companies here in SA sell them as an upgrade kit.
Technical Bgger carb
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Technical Bgger carb
Well, in conjunction with a cam change, I expect it would give 10-15 bhp or so - also, bear in mind that the carb jetting is probably all different. I suspect that if you took the same jetting and put it in the 32, you'd also get a performance increase.
Also, that standard '32' sounds like a lot more than the size of the venturi (where the main jet exits) which I think is more like 24mm. I suspect that, again, the 34 carb also has a larger venturi.
On my 128's 1498cc engine, I had twin 40DNCFs fitted with 32mm venturis - four of them! - effectively one carburettor per cylinder. The main jets etc. were about as large as the main jet in a single carb. The reason? There's only one cylinder creating the depression at any time (in a four-cylinder engine) so the single carb is really set up for only one cylinder.
The other reason - a larger venturi gives less of a depression (i.e. vacuum) than a smaller venturi, so the jet size needs to be larger to allow the same amount of petrol through.
This negates to some extent the statement I made about the same jetting in a smaller carb giving similar performance - but, there's more than one variable (as well as the main jet, there's the air corrector (bleed), the idle jet, the venturi size, and the accelerator pump jet...)
Some people say that over-large carburettors will give poor low-speed running and poor economy due to the insufficient vacuum giving poor fuel atomisation. In theory, this also makes cold-running difficult.
In reality, my 40DCNFs had no choke flaps (or cold start devices) and yet the starting was not only easier than with the standard carburettor, the engine would actually idle when cold (slowly), and the economy was 2mpg better than standard... what more could you want?
Some carburettor swaps do not go so well, but I'd say it's worth a try.
-Alex
Also, that standard '32' sounds like a lot more than the size of the venturi (where the main jet exits) which I think is more like 24mm. I suspect that, again, the 34 carb also has a larger venturi.
On my 128's 1498cc engine, I had twin 40DNCFs fitted with 32mm venturis - four of them! - effectively one carburettor per cylinder. The main jets etc. were about as large as the main jet in a single carb. The reason? There's only one cylinder creating the depression at any time (in a four-cylinder engine) so the single carb is really set up for only one cylinder.
The other reason - a larger venturi gives less of a depression (i.e. vacuum) than a smaller venturi, so the jet size needs to be larger to allow the same amount of petrol through.
This negates to some extent the statement I made about the same jetting in a smaller carb giving similar performance - but, there's more than one variable (as well as the main jet, there's the air corrector (bleed), the idle jet, the venturi size, and the accelerator pump jet...)
Some people say that over-large carburettors will give poor low-speed running and poor economy due to the insufficient vacuum giving poor fuel atomisation. In theory, this also makes cold-running difficult.
In reality, my 40DCNFs had no choke flaps (or cold start devices) and yet the starting was not only easier than with the standard carburettor, the engine would actually idle when cold (slowly), and the economy was 2mpg better than standard... what more could you want?
Some carburettor swaps do not go so well, but I'd say it's worth a try.
-Alex
OP
OP
thanks for the reply, will buy it and see if it gives me a power increase while i wait for my project to be finished.
Good plan 
Do a two-way speed run down one of those awesome roads that you have over there (I remember a thrilling ride in an Uno Turbo boosting over two bar on the way back to Sturdee Avenue from some dragway somewhere).
Time your 0-100km/h and of course test the top speed. Currently? I'd imagine 11 seconds and top speed 158?
-Alex
Do a two-way speed run down one of those awesome roads that you have over there (I remember a thrilling ride in an Uno Turbo boosting over two bar on the way back to Sturdee Avenue from some dragway somewhere).
Time your 0-100km/h and of course test the top speed. Currently? I'd imagine 11 seconds and top speed 158?
-Alex
