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MG MGB Technical - Setting up a Weber 45DCOE - Help!

Does anyone have any advice on setting up a Weber 45DCOE??

I have a 67 GT with the following engine mods: 1840cc, Oselli Stage 3 head, Kent fast road cam, 2in freeflow exhaust, Lucas 45D4 dizzy, Facet performance fuel pump & regulator.

I am using the long manifold and ram pipes on the Weber. The settings at present are:

Choke: 36
Main jet: 145
Idle: 55 F8
Air jet: 170
Emulsion tube: F9
Pump: 40
Starter jet: 85 F9
Starter air jet: 150

The Weber is in good condition, but it was removed from another MGB, I do not know the state of tune of the engine except that it had a Piper performance dizzy. The present settings seem to be too weak, I don't have any experience using Weber carbs which so I need some advice about what to change!

Starting from cold it runs pretty rough, it coughs and splutters, but runs reasonably ok once warmed up. Once warmed up it ticks over at about 800-900 - not particularly smooth. When pulling away from a standstill it hesitates and needs quite a lot of revs to pull away smoothly. If I try to pull away reasonably quickly and I open the throttle quite quickly as I bring up the clutch it splutters & chugs and takes a second or 2 to pick up - almost like its run out of petrol. If at tickover I open the throttle a little the revs actually decrease and it runs rougher, increase it a bit more and the revs increase and it runs smoother. Cruising at 2500+rpm it runs pretty smooth, but the biggest problem is trying to drive at a constant 2000rpm. It splutters and chugs and runs really unevenly, once you open up the throttle more and accelerate to a constant 2500rpm it evens out and runs ok. This gets to be a real problem when trying to drive around town!

I know this is like asking the impossible where setting up Webers is concerned but if anyone has any advice to offer I would be very grateful. I don’t know what the standard settings are for an MGB Weber kit, so I expect this would be a good starting point, are my settings way off??


Thanks in advance for any advice!

Paul Grundy

Standard set up for a B is

Choke 36
Emulsion tube F16
Main jet 170
Air jet 155
Pump jet 50
Idler jet 50F8
Aux venturi 3.5


Fast road set up is

Choke 38
Emulsion tube F16
Main jet 175
Air jet 160
Pump jet 50
Idler jet 50F8
Aux venturi 3.5
Chris Betson

Yours sounds more like it is jetted for a 1275 A series. It struggles because the main jet and pump jet are way too small as you can see from the figures Chris has posted.

The F9 emulsion tube ought to be able to work ok though a different tube might suit it better, not certain I would go for the F16 though.

You don't say what Aux venturi you are using and this will have an influence on the main jet size at extremes eg 3.5 or 5.0.

With a fast road cam (exactly what?) you can't expect a lot at 2000rpm especially on a DCOE.

Is the distributor vacuum advance closed off (as it should be when using a DCOE).
Daniel

Also sounds like you may need to advance your timing. DCOEs like a lot more advance than stock Bs, I think.
Baxter

Thanks for your help guys,looking at the figures Chris has posted I can see why it runs like it does! Oh I meant to say I have the 43D dizzy with no advance,not the 45. I think I'll use the standard settings as a starting point and work from there. Thanks for your help, much appreciated!
Paul Grundy

This thread was discussed between 01/03/2003 and 02/03/2003

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