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MG MGB Technical - Weber Low End Running Bad

OK Guys - a few of you have been down this path I'll bet. Put on a Weber sidedraft. Car always ran great on the SU's, but you know how we can be - never content!

Full choke and it runs REALLY bad on start up and pretty bad up to temp - you'd think I had Hilborn injection or something! I am suspecting a combination of accel pump jets and low speed jets - pump is working and emits a healthy stream.

What jets should I be running and where do I buy them?

Cheers and Merry Christmas!
Norm Tucker

Norm-
What other modifications have you made to the engine? If it is otherwise stock, put the SU's back on as the Weber DCOE provides no advantages on a stock engine.
Steve S.

If you are going to use the DCOE this link should have enough resources to help you get started. Be prepared to spend lots of time getting it sorted.
http://www.teglerizer.com/dcoe/webertune.htm

Clifton
Clifton Gordon

Steve - yes the motor has a mild cam, mallory dual point and hotter coil - but judging from the comments by Clif's reference article = pain in butt to set up - muchmore so than SU's = I will say that once the car gets over the stumble and cleans out it makes red line like a rocket!

Maybe a small block Chevy, hmmm?
norm tucker

First things first.

Have done an size inventory of all of the jets and tubes and float
chamber valve?

If so...what are they?

What manifold are you using?

Does the Mallory have full mechanical advance - or vacuum?

Daniel Wong

There is a wealth of information at the Pierce Manifolds website.
www.piercemanifolds.com
Pete W.

You shouldn't really need the choke for a DCOE; kick the accelerator 3 times from cold, 5 on a freezing morning, never when hot, then turn the key. I've left mine disconnected for years now and have never missed it.
Steve Postins

I ran a Weber 45 DCOE for almost 20 years before installing a Moss supercharger. It indeed is dificult to set up without a rolling road. After a lot of trial and error, mostly error, these are the the settings that I used with a mild cam and mechanical advance Mallory dual point: 36mm chokes,5.0 aux venturies,F16 emulsion tubes,60 F9 idle jets,160 main jets,60 pump jet and a blocked off discharge jet. I drilled out the starting jets as the car was used in a cold climate. I was able to purchase the parts through Seven Enterprises. Beware as the parts are not cheap and you will require two of each item except for the fuel pump circuit. Ray
RAY

Norm - I was thinking about the advice that's been on the board before. You may never get the Weber set up based on your description of your engine. Most posters have said that the side draft Webers require major engine work - fast cams, bigger valves, relieved ports, headers, high compression, etc. The point being that the near stock engine you have does not pump enough air to match the capability of your carb. It's roughly similar to the advice given for bigger SU's as well. The carb should match the flow requirements of the engine (it is a system, afterall). Currently, it will especially stumble at low flow rates.

You don't need a Chevy small block. If you build up your B-series engine and then screw on the Weber (AND adjust it properly) you will have a screamer. It just that all the components have to work in harmony.
John Z

Once you have a relatativly balanced setup the choke size and the auxilluary venturi sixe will make for a much more tractable engine. Enen though the sidedraft Weber gets a lousy rep from people who failed to set it up properly, once it is dialed in it is really an excellent and very flexible carb that stays in tune. Ray
RAY

This thread was discussed between 18/12/2007 and 21/12/2007

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