On the base models they used an exhaust manifold that was also part of the inlet manifold, it was meant to warm the fuel mixture on the way in to help economy and warm up (also cheap to make), if you buy an MG alloy inlet and then fit a proper exhaust you get a decent power increase (especially if you clean up the inlet), then you just buy a new needle for the SU from someone like avonbar and it will go much better. If you really rag the car on the current set up it will eventually conk out until the inlet cools enough to get going again, it took me a lot of break downs to find out why it was doing it.