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MG Midget and Sprite Technical - weber 45 vacum take off

Hi All, I have just bought a 1275 midget with a twin choke 45 weber. Currently there is no vacume take off to the distributer there is a brake servo fitted.

Can anyone tell me were the takoff point should be ? does it need to be just behind the throttle butterfly on the engine side or can it be anywhere downstream.
Ben Brown

Ben
Iwouldn't bother with it-more trouble than it's worth
Normally the dist. vac. takeoff point would be just outside the butterfly so that there is no vac. at idle but as the butterfly opens above idle the dist. will start getting a vac. supply which will increase a bit at part throttle and drop out nearing the second half of throttle application
The problem with a 45 on a little engine is that compared to a pair of smaller carbs you don't need as much throttle opening for fast cruising and where say for example you are cruising up a slight climb on the feeway at a good pace - On the smaller carbs you would be well into the throttle past the point where vac. is being supplied to the dist.-BUT because the 45 has bigger butterflies the throttle is less open and still sucking the dist.advance on and will/can cause detonation
Much better to get your dizzy recurved to suit your engine specs and forget about vac.

In my humble opinion - specially if the car is going to be driven in a spirited manner,-- which is why we have webers afterall
Cheers Willy
WilliamRevit

I've a take off adapter which fits between the servo fitting & the manifold. I'm using an Aldon dizzy with a modified curve for my engine, though changing over to mapable crank fired ignition soon.
Brad 1380

Agree with Willy - and if the car is already fitted with a DCOE then the dizzy may have been modified to suit already - if you connect up a vacuum advance to a pre-modified dizzy you run substantial risk of melted pistons... Just cos' its fitted with a VA unit doesn't mean it isn't modded...

Might be worth talking to the previous owner

FWIW

JB
James B

Thanks guys I dont think the dizzy has been modified but cant be sure, the previous owner was not technically minded so wouldn't know. So from your posts I wouldn't be able to simply take vacume off any where downstream of the butterflies then.

On SU's I think the pickup is downstream of the butterfies as you do get vacume at idle

And yes I do drive the car 'spirited' but often there is some one in front in a dull box spoiling the fun.
Ben Brown

This thread was discussed between 07/08/2010 and 08/08/2010

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