Classic/Antique Car Repair: 1972 MGB, stale gas, hydraulic resistance

Question
Howard I have recently purchased a 1972MGB, It has been stored in a shed for the last three years without running.  The first thing I did was purchase a new battery,plugs changed fluids all the easy stuff first. Supprisingly it did start but runs pretty rough.  My question to you is, should I dive into the carbs right away or run it for awile?  Also I did put fresh gas in and carb cleaner.  

Answer
Hi Matt,
I would not run it very much if it is not running right as you may do a lot of damage depending on what is wrong.
My first question is, did you add new gas to some old stale gas or did you drain the old and put in new? When I worked in dealerships and my own shops and had MGs brought to me to get running that had been stored for some time I would drain all fluids and replace them with new fluids, then do a "Wet" and a "Dry" compression test. Do the "Dry" test first. A "Dry" test is just a normal compression test (throttle open). You should see 135 PSI to 170 PSI on all cylinders (allow at least 4 or 5 rotations of the crank.) Then do a "Wet" test which is just put several squirts of engine oil (about a teaspoon) into the plug hole and do a compression test (throttle open). You should see a little higher numbers than the "Dry" tests. If there is a large difference between the two tests, you either have a ring problem or rust on the cylinder wall or stuck rings.
If it is OK check the ignition timing. If this is OK then remove the air filters and examine them and if dirty blow them out with compressed air or replace them. Unscrew the caps on the top of the carb pots. Lift each one up and push them back down. If you feel hydraulic resistance they are OK if there is no resistance put several squirts of engine oil in the top and put the small piston on the end of the pin back in to the pot and tighten the cap. Start the engine and warm it up. When it is warmed up and at idle find the small pin sticking down from the front pot on the side and lift it as far up as it will go. The engine should drop RPM and start running like an old John Deer tractor. If the engine stalls the rear carb is either too lean or the front and rear throttles are not in sync. If the engine speeds up when you lift the pin the rear carb is too rich. Rev the engine a couple of times between each check to clear it. When you get it to drop off and run like a two cylinder engine go to the rear carb and do the same thing. When that one is done reinstall the air filters and road test the car to see if you still have a problem.
I found on some stored MGs that they would run ok at lower throttle settings but it you accelerated hard the engine would get flat as though it had a rev limiter. This is most likely a stopped up muffler due to rust and corrosion. An exhaust back pressure test is needed (1 1/2 PSI max at high throttle settings)
I hope this helps, let me know.
Howard