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40 mm Weber and 1275 engine

Posted by 1275- ron 
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Ron Hermanson
CA, USA   usa

Will the the 40 mm side draft Weber carb. work on a 1275 engine?

Ron

P P
O, Ontario, Canada   can
1967 MG MGB GT "Maggie (GT From Hell)"

Yes, if you set it up with the right parts. The 40 should be a good match for the 1275. You need to do a bit of searching to get some baseline set-ups for the midget. What is tricky with these carbs is that there seems to be a few ways to arrive at a good setting, so different people are going to suggest different set-ups!

Do you have any idea of the current ventury and jet values?

Pete

7mg2 Avatar
Andrew Hardie
Calgary, Alberta, Canada   can
1969 MG MGC GT "Mr "C""
1972 MG Midget

Ron,
stick with SU's if I were you. Weber looks impressive, but SU's are better suited to these engines for road use. As Peter says, so many ways to set these things up, and everyone does it a little differently it seems. Dual carb set ups are what seem to intimidate folks the most, but they are actually easier to set up and keep in tune ironically, especially if you stay with the HS2's the car came with.
The 40mm you asked about will certainly work on your 1275 tho'



Andy

NAMGBR# 20-7738
AMGCRA# 1678

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moreso74 Avatar
David Maples
Augusta, Georgia, USA   usa

A 45 will work too. And, like the 40, there will be a significant tuning time requirement for initial setup.
Both of these carbs will really only be of use if the engine has been "worked over" well.
Both are big carbs and to be of use, the engine has to be made to breathe a LOT more than stock.
= ported head, lumpy cam, compression bump to 9.2, tubular LMB header

Expect your gas mileage to drop.
Tom Bedenbaugh used to drive his to work every day.



David

P P
O, Ontario, Canada   can
1967 MG MGB GT "Maggie (GT From Hell)"

I suggest that it is a misconception that an engine has to be Tuned in order to benefit from a DCOE carb. The carb could care less what state of tune your engine is in.

A carburator, any carburator including the DCOE, is a calibrated fuel leak that responds to the air your engine pumps. The carburator has no way of knowing if the engine is stock or modified. A modified engine is just a more efficient air pump.

Your job as a carb tuner is to set the carb up to feed the proper fuel ratio to whatever airstream is going down the ventury. In the case of the DCOE, this starts with actually selecting the ventury for the engine application and desired use of said engine. The carb is adjusted to work with the engine, not the other way around.

The truth is that a tuned engine can benefit from a DCOE since he carb can be set to take advantage of the improved air pump.

A stock MG engine SHOULD enjoy better throttle response with a DCOE due to the accelerator pump, feature however the irony is that most of us end up with a bog in the transition to accelration when we use these carbs. Go figure...

Pete

Art Hughes
Ohio, USA   usa

Contact a Weber dealer. They will be able to sell you the correct Idle fuel jets, main fuel jets, air corrector jets, and proper Venturi size. They will have recommend starting ponts, and can advise you.
Weber carbs have to be adjusted properly, or you will get a bog. The old "turn it 1/4 turns until it idles" WILL NOT make it operate correctly. You have to have proper idle speed, and realize that for a Weber, 1/16 turn of the mixture screw is a big adjustment. If you gain RPM with idle mixture adjustment you have to drop the idle down, and adjust some more. If you screw with it too long at idle, you overheat the intake and the carb, and gain nothing. With wrong jets, will never run right.

The down draft Weber is always jetted wrong, especially the idle jet, which is 1-2 sizes too small. Best to call a Weber dealer and get the right things.

tim65mgb Avatar
Tim Guntly
Cherry Valley, Illinois, USA   usa
1960 Daimler V8-250 "SP250"
1967 Daimler V8-250 "Delany"
2013 Mazda 3

I would say stay with SU. Unless you want your car to sound like you are driving a vacuum cleaner. I also noticed no sizable difference in performance but did note less fuel milage.



Edited 1 time(s). Last edit at 2010-04-07 10:17 PM by tim65mgb.

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P P
O, Ontario, Canada   can
1967 MG MGB GT "Maggie (GT From Hell)"

Ron:

I am just finishing the tune on the DCOE on my MGB. Here is a link to a site that really helped.

http://www.tjwakeman.net/TR/WeberDCOEinfo.htm

The article breaks down the process so it is easy to understand. I was able to see that the so called expert who set my carb up years ago did a lousy job.

The idle setting on a DCOE is unlike any other carb. It is the foundation to the set-up and vital that it be done right if the thing is going to work well and deliver decent fuel mileage. After many years of living with the bog and poor fueld consumption, I have the thing running like it should.

Pete

Bryanm362 Avatar
Bryan Matthews
Cincinnati, Ohio, USA   usa

In reply to a post by NOHOME
A stock MG engine SHOULD enjoy better throttle response with a DCOE due to the accelerator pump, feature however the irony is that most of us end up with a bog in the transition to accelration when we use these carbs. Go figure...

Pete

How can I correct the bog down, when going from idle to acceleration?

P P
O, Ontario, Canada   can
1967 MG MGB GT "Maggie (GT From Hell)"

Bryan:

The secret to setting these carbs up is the the idle. You need to get the engine running smooth with the screw that adjust the butterflies open AT MOST 1/2 turn. Until you do that, the job is impossible.

Read the link I posted. It covers idle setting and what happens when the throttle opens.
Another thing is that before the carb can be set, the spark ahs to be perfect.

Pete

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