Classic/Antique Car Repair: Mg Midget, rubber diaphragms, dual carbs

Question
I have recently taken my MG midget out of storage-8 years-. When I quit using it, it would not start after the engine was warm.  Recently, my mechanics (very good on American cars) replaced almost everything in the fuel and electical distribution.  Drained the tank, new fuel, new tires, new oil, etc.  I drove it away from the shop, and it ran better than it ever did for about 10 miles, when it started missing and eventually dying. Started back up, but still missing.  After several starts it made it home - limping.  Next day, It ran well for about two miles and the same thing happened. My mechanic will make good on it, since I have spent a lot of money with him over the years, but what is wrong? Anything I can suggest. The mechanic who worked on it did have some experience in the 60's and 70's.  Thanks  

Answer
You can't tell what is wrong untill he runs tests on it to see if it is fuel related or ignition related. Since it has been in storage for so long it is probably fuel related as even though he cleaned out the system it most likely has a lot of varnish in the whole fuel system and the new fuel can brake a lot of that stuff loose as you drive it. He may also have put an addative in the tank to help clean that stuff out and it can get loose and work it's way into the dual carbs or single carb if it is a 75 or later. From what you say he probably did what he was supose to do. You didn't tell me what year it was so if it doesn't have an inline filter in the fuel line just before the carburetor / s have him install one and check fuel pump pressure as most British car pumps (electric or mechanical) don't fair well setting for 10 years. Both electric and mechanical pumps have rubber diaphragms and they harden and don't work well after setting for a long time. That is about all I can add. It sounds like he knows what he is doing so let him run the tests and if it is fuel related suggest that he add a filter and be prepared to change it often for a while.
If it has two carburetors they are SUs and if it has just one, it is a Stromberg. If there is a problem there, I can help as even a good domestic car mechanic may not know these carbs. let me know.
Howard