MG Car Repair: 1968 midget 1275cc, vacuum gauge, manifold vacuum

Question
lose power in fourth gear.  all of the other gears expecially the third gear run up great

Answer
Hi Ron,
Unless you have a gearbox freezing up the engine don't know what gear you are in. So you need to put a manifold vacuum gauge on the intake manifold and run a long hose out from under the hood and place the vacuum gauge under a wiper arm so you can monitor vacuum as you drive. Note the reverse progression of vacuum as you accelerate from idle and on up through the gears. Write down what it goes from / to in each gear and let me know.

Also, is the engine smooth as it looses power? or is it missing and running rough?
Howard