new "B" with "old" carbs/exhaust question

[Patricofnj]

Hi,
My son acquired from a friend of his an unexecuted father-son project in the form of a 1977 "B". It is in pretty good shape, has 45k miles on it. It sat many years, we have flushed the motor, rebuilt/replaced brakes etc. The previous owners took the weber downdraft setup and went back to the dual SU sidedraft carbs. Along with that the manifolds had to be changed as well. when that happened a direct hookup to the catalytic exhaust system was impossible. We do not have the original carbs etc. My question is: can I fabricate in a catalytic converter onto the older style system with out runniing into issues with backpressure and who knows what else. The balance of the emission control system remained with the car. I need to explore this avenue since the car will not pass state examination without the cat installed and registering the car as historic or classic limits the type of driving one can do. My son is looking for a daily driver. Any suggestions appreciated.:uncomfortableness:

 

[aeronca65t]

Welcome Patrick!

I also live in NJ and have an MGB (but it's a '69, so no catalytic converter).
In my case, I elected to register my car as a classic, so no NJ inspection; I have a Miata for normal use and the MGB sees about 1500 miles in the Summer.

Anyway, back to your issue: I would sort of think the original manifold and converter would not be hard to find used on e-Bay or through local MG clubs.

Otherwise you might be able to buy a short converter from Summit Racing and put it under the car instead of the stock location (it's normally attached to the exhaust manifold). But on these cars, the converters work best when they are close to the exhaust manifold, so you'd have it close to the engine......probably under your feet (maybe create some sort of heat shield?). The '77 is pretty high if it's stock so there is room, but if it's been lowered, this may make things more difficult. And it's hard to say if a twin-SU carb and a catalytic converter would combine to pass emissions. No telling.

If you want to go through NJ inspection, I would guess the easiest thing would be to source the original single carb manifold and converter that fits the exhaust manifold. Lots of folks complain about the original Zenith single carb on the '77, but honestly, it's not that bad if it's clean and has a new diaphragm (a key component).

One place to look for these used parts would be at Britfest here in NJ on May 4th. Here's a link to Britffest:

https://www.mgccnj.org/flyers/Britfest 2013 Registration.pdf

Otherwise, there are local British car clubs in central and south Jersey that might have events where there will be flea markets (not everyone would bring something like this, so you may have to ask each used parts vendor if you go to an event).

One good club down near you is Positive Earth Driver's Club. You might find someone via the club with these parts fairly cheap.
Link to PEDC:

https://pedc.org/

You could also try:

Doug's MG Shop (732)919-0771
1038 State Route 33, Freehold, NJ 07728

Decent guy with lots of used MG stuff.

Finally, don't forget Car-Part.com. This is a great way to locate hard-to-find parts.

https://www.car-part.com/

Here's an image from Moss Motors on the correct setup (cat is #60):

 

[DrEntropy]

I second Nial's Welcome!

And his suggestions are about the only way to get a '77 B through the emissions test short of re-engineering the entire induction/exhaust system.

 

[PAUL161]

I agree with Nial and Doc, but in the Moss illustration, no 63 is not available from them. To the unknowing it can cause more confusion. The original type cat and carb set up is very important and as said, must be replaced, but I wouldn't think the exhaust pipe and muffler, #63, should matter for pollution purposes, just sound. PJ