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MG MGB Technical - carburator conversion

I am converting my 75b from zs carburators to su. The su's will not fit up to the car with the cowling side carburator's air cleaner fitted. The metal opening of the carburator touches the brake booster. I read in the archives of 2 intake manifolds numbered 12h3911 and 12h709. My intake manifold is numbered 12h2568. Is this the wrong manifold for an rb conversion or do I have to look further?
kra Karl

Kra, I don't think the stock aircleaners will fit with
stock 1975 booster in place. I think you will have to go with some rather small aftermarket cleaners to make things fit. RIC

I have k and n air filters for these carbs but had them removed from the carb when trying to fit. It would not have been possible to put any filter on the carb. The metal carb throat was against the brake booster.
kra Karl

i have used the oval foam air cleaners available from moss or victoria british since the late 80s with no problems. however the actual filter elements are now only available thru vb. you will have to put a dimple in the rear mesh cover to correspond with the brake booster. carefully done with a ball peen hammer.
bill dwyer

Bill and Rick
Thanks for your responses. Your right Rick the new k and n ones I purchased for this project are not going to fit without some alterations. Are there aftermarket brake boosters that are smaller and do allow more room ? Are there other alternatives such as changing the angle of fit by machining an angle into the spacers or shortening the spacers?
kra Karl

What you propose sounds like the a good solution.
kra Karl

You should get your son to help you.

Has anyone tried to use the ultra thin Stellings and Hellings air filters in these tight spots? I probably have about 1 inch of space between the end of the carburator and the brake booster.
kra Karl

As I read over the posts I thought of the air filters from Austin Healey 3000s with triple HS4s. Another item that came to mind was the cold air box fitted to the 100M Healeys. Were you to build a cold air box to fit your car then you could fit a cold air duct to it and connect it to a remote filter.Check out the Moss
listings for pictures of the mentioned parts. RIC

Kra check out e-bay item 280332638467 what do they say about pictures and words? RIC

There's a black phenolic spacer that I had to saw in half to make the twin SU's fit in my '77 B. That, along with K&N conical air filters did the trick.
If you want photos, or more info, send me a note at
Randy Olson

FWIW gentlemen: On a recent dyno day of my 77 MGB which is setup pretty much as KRA above, last run was done with conical K&N air filters removed. The RWHP went from 73- 83. Since I've found racing air boxes available anyway, any size you might want. Not cheap, but if you look from the back to front, that is the cheapest 10 ponies you will ever get.......that of course until you move up to a Moss SC which gave me 123 RWHP, 133# torgue and a flat AF between 12.5-13.
See upload below. Cheers VEM

vem myers

This thread was discussed between 26/03/2009 and 11/04/2009

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.