MG Car Repair: rough running mg midget at high speeds, fuel pressure gauge, fuel compression

Question
I am in the process of restoring a 1979 mg midget, Have added the following, weber carb, headers,electronic  ignition , new fuel tank, but engine seems to be rough at higher speeds. Any suggestions?

Answer
Hi Mitch,
Running rough at high speeds narrows the problem down to only a thousand possible things. You will need to do some testing to get it down a little closer.
All engines require three items to run and each item has conditions.
1. Compression
2. Fire
3. Fuel

Compression must be sufficient. Run a compression test. It should be from 135 to 180 PSI with little variation between cylinders.

Fire (Spark) must be a good spark (thick blue spark)and at the correct time (timing set to factory specs. Plugs must be the correct heat range and clean. The ignition system should be tested on a scope.

Fuel must be a combustible fuel available to each combustion chamber in the correct fuel/air ratio. First you must be sure fuel pressure is correct at the carburetor at the time of rough running. To do this you need to put a "T" in the fuel line close to the carb (with clamps) and run a hose out from under the hood and put a fuel pressure gauge under a wiper arm so you can monitor fuel pressure at the time of rough running. Fuel pressure should be 1.5 to 3 PSI at all times. Then you need to confirm that the correct main jet was installed in the Weber for the kind of car you put it on.

One more test should be run and that is exhaust back pressure. The exhaust back pressure must not exceed 1.5 PSI at high speed and high loads.
Howard