Classic/Antique Car Repair: Triumph Spitfire, pipe leaks, muffler shop

Question
I have a '75 spitfire which I have owned for about 15 years.
I have a problem that has been nagging me since I bought the car, and seems to have progressively gotten worse over the years. When I drive it, I get a very strong "exhaust smell" in the car.  It pretty much permeates my clothing hair etc. and makes me nauseaus.   The problem seems to be noticeably worse when the top is down.  I have had it to a muffler shop and they assure me that there is no exhaust leak.   Somebody suggested that it might be something to do with the carburetor mixing the fuel too rich,(only one carb on this one, my '64 had two) I've adjusted the choke cable linkage to ensure that the choke opens completely, and that made no difference. I have had other convertibles and one other spitfire but this is my only car that ever exhibited this problem.

I certainly don't expect you to miraculously fix my car over the internet, but if you might help to point me toward a possible cause I would be eternally grateful. Perhaps something that is an idiosyncrasy of those rascally little spitfires or something along those lines... Right now My wife refuses to ride with me, and I certainly can't blame her.  I'm getting kind of tired of my work mates knowing that I drove the spitfire as soon as I'm within smelling distance.

Answer
Hi Mark,
I have not run into this on a Spitfire but have on other cars. You should have the CO & HC checked to make sure the exhause itself is not a problem. If that is OK, you already know you don't have any pipe leaks. Than I would look toward aerodynamics. Meaning when you drive with the top down the wind screen makes a low pressure area just behind it (where you are) This lower pressure area can extend all the way to the rear of the car which can pull exhaust fumes to you from the rear. If this were my car, would try two things. Your model still has the fresh air vent in front of the windscreen? Open it when the top is down. It will not completely eliminate the low pressure area in the cockpit but it will decrease it. Also I would get one of those tail pipe ends that deflect the exhaust downward to help defuse the exhaust into the air stream coming under the car and helping to keep it from comiing up to the low pressure area behind the windscreen.