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MG MGB Technical - Air injection manifold plugged or not? - 76B

On my 76B, the air pump and gulp valve have been removed by the PO. The place the gulp valve was mounted is plugged. However, the air injection manifold is still in place. At the end, it looks like the PO just cut the hose and left it open. Should that hose be plugged or remain open?

FWIW - in Georgia, 25 year old cars do not have to pass emission tests.

Thank you.

John English

The air injection manifold should be removed and the threaded holes in the head closed off with screws. The check valve on the air manifold will hold the exhaust pulses, with the occasional leak, but the tubing that makes up the air injection manifold will rust and get holes in it from the inside out. Mine did that in about a year's time especially in the 180 degreee bend.

Wayne Pearson

Most people when removing the air pump and its components remove the rail completely and plug the holes with a brass, or other material, screw. The screws are available on eBay:

I believe that left open you are allowing unfiltered air to enter the combustion chambers which could cause a host of problems and creating a vacuum leak which could affect performance, although I might be wrong. Removing the air rail will also clean up the engines appearance a bit.


Take it off. It does not affect performance but is in the way/ugly. It will rust out as Wayne said, then causing an exhaust leak, and sucking air into exhaust on overrun, giving backfire. Best is allen set screws, 7/16-20 (fine)x 3/8 long - these are standard for certain sizes of keyed shafts/pulleys, so are pretty easy to find in a good hardware or parts store. You can use a long sheetmetal screw to pull the air injection nozzles out of the holes in the head, or just leave them. In either case, it is best to put a 1/4 ball bearing under the setscrew, so that the screw can seat and seal without damaging the threads in the head. The threads do not go all the way to the bottom of the hole, which is tapered at the bottom.
FR Millmore

My local supplier, Atlanta Imported, has the plugs like the e-bay ones in stock for a dollar a piece, so I'll pick some up there. I'll be glad to get this thing out of the way - it will make spark plug changing easier.

Thanks for the informatin!

John English

I just used an appropriately threaded bolt I had lying about and cut it into plugs, filed the ends smooth and cut a screwdriver slot into one end with a Dremmel. I painted them the same colour as the block and you can hardly see them.

Simon Jansen

I have a 77 MGB that still has all the emissions stuff on it. Is there anywhere that give an amatuer step by step instruction how to remove it? I don't need to pass emissions any longer. If I do remove it, does it improve performance/horsepower?

Thanks in advance!

Bill, from what I've read in the archives, John Twist's technical manual, available at his site, has a step by step procedure for removing the emissions stuff from a 75-80 MGB. Here's the link that tells you how to order it.

You might want to call them and make sure that article is in the current book before you order. From what I understand, the manual is updated occasionally.

Hope this helps.

John English

Thanks for the link... Unfortunately when I went to that site, the link to get to the articles did not work. So, if anyone else has any idea where I can go for instructions for removing the emissions junk off my 77 B, I would very much appreciate it!


John Twist's instructions are in Lindsay Porter's "MGB Purchase and Restoration Guide".

Clifton Gordon

Clifton is right. It even has pictures. I just received mine from Amazon. It's now called "mgb restoration Manual". ISBN # 1859606075. Here's the link at Amazon:

John English

You guys are great! Thanks for the help, I just ordered it. The smog emissions should be gone within a week.

Thanks again!

BILL in Maryland

This thread was discussed between 30/06/2005 and 02/07/2005

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