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MG MGB Technical - 40 DCOE on fast road B

I'm currently running a 45 DCOE with the long inlet manifold on my fast road built B series but I want to swap down to a 40 DCOE.
I've just bought myself two twin 40s on a Pinto manifold so I'm half way there!

I just have a couple of questions about swapping down to the 40.
Firstly (I think I already know the answer to this one!) is there different manifolds for the 45 and the 40 due to the differing venturi sizes?

Can anyone provide me / point me towards a rough starting ground for jet sizes etc using a 40 on a fast road B?

Also does anyone know how much lift the accelerator pump rod should provide for a B series? This is one thing I never got round to changing on the current 45.

One more quicky, which manifold does everyone here generally prefer the long or the short? I've heard the short manifold can give uneven fuel distribution.
K Goldup

First why swop down?
If it is for fuel economy go back to SU's as that will give a bigger gain.

40's and 45's both fit the same manifolds.

On average you always want the longest inlet possible for better torque so go for the long manifold.
Onno K

Fuel economy doesn't come into it when I'm involved!
I want to try and regain some bottom end grunt and some drive ability.
K Goldup

Go for a smaler choke not a smaler carb.
Even on a 1275 A-series a 40 is considered small (though doable) and a wel setup 45 usualy gives beter results (even low down)

Go to a good roling road to have the 45 setup and you should be able to regain any torque present in the engine
Onno K

X2 - just select a suitable main venturi for the 45 - there is no reason to go down to the 40, which I agree is nearing the top range of available sizes (36 for the 40 DCOE, and 40 mm for the 45 DCOE)
Bill Spohn

Yep
45 should be fine on a 'b'
I ran a 45 with 40mm choke for ages with 185 jet F2 emulsion tube and if I rememder correctly 160 air
Ran as smooth as
Willy
William Revit

This thread was discussed between 26/08/2012 and 29/08/2012

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