'92 Metro 1.0 Exhaust Question -- pipe diameter

I had my exhaust replaced a little while ago, from the head pipe back, including the catalytic converter.

The O.E.M. exhaust included a double-walled section of pipe, between the catalytic converter outlet and that small resonator in the middle of the car.

The muffler shop replaced that section with the smallest pipe they had -- an inch and a third in diameter. I failed my license plate renewal emissions test not long after this was done, and I'm wondering if the larger (?) diameter of the relacement pipe has had something to do with that. I'm guessing that the slow-down in gas velocity because of the wider (?) pipe diameter (and also because of the quicker cool-down of the gas, in the non-insulated, single-walled replacement pipe) is at least partly responsible for this, but I'm not 100% sure. Whatever it is, my spark plugs are sooting up, my gas mileage is way down, and the emissions test showed way high levels of "unburned hydrocarbon" gasses.

Does anyone know of a parts outfit that has OEM Metro exhaust, that would tell me what the I.D. (Inside Diameter) of that double-walled pipe is?

Thanks,

Mike

The original is about 1.25, you've got practically the same thing. Some guys run 2 inch, that's not your problem. Your car is running rich, could be a bad O2 sensor, leaky injector, or failed fuel prssure regulator. That might be why you needed a new cat in the first place.

Thanks for the taking the time to clue me in.

I replaced the O2 sensor when I got the car, and rust is what killed the cat, but I'll have to have somone check the injector and/or fuel pressure regulator.

Much obliged.