MG Car Repair: 69 MGB - Rough Running After Storage, summer siesta, piston head

Question
1969 MGB US - GHN4U

My car (I have owned it for 41 years - 9,100 miles since overhaul)was put away and not run for the Nevada summer (two months).

Last Spring it was running quite well, but after a two month siesta, it starts but runs very rough.  After rebuilding the ignition system, new plugs, wires, cap, coil and checking valve clearances - it still runs very rough!  Pulling the plug wire on # 2 cylinder has no effect on the engine speed (others will drop the rpm).  Dry compression on all cylinders runs at 130 psi +/- 5 psi.  Pulling the plugs at looking at the piston head, # 2 is oily (but the plug is a nice tan color) the others dry.

The fuel supply line from the fuel bowl have been replaced prior to it's summer siesta, but other than that nothing has changed.

I do not really want to pull the head if the culprit is somewhere else and why would it be running great and then suddenly go rough?

Ideas?

Thanks,

Answer
Hi Mike.  After 41 years you probably know your MGB very well, and you would immediately recognize if something was wrong with her.

The good news is that your compressions are all within 5psi.  That confirms to me that you do not need to take the head off.

I am concerned that the problem seems to be with #2 cylinder only.  The front carburetter is shared between cylinders #1 and #2, and there is a drop in rpm when you pull ignition wire #1 which pretty much rules out the carburetters.  I would still check that the dashpots are full of oil though.  And I would check that the front float chamber is full of gas.  Needle valves do stick sometimes.  

I really think this is an ignition problem.  

My immediate reaction would be to replace #2 spark plug and #2 HT wire, but you have already done that.  

If you are still running with points ignition, then it might be worth replacing the condenser -they only cost pennies.  Also, double check the setting of the points.  

It would be a good idea to make sure that you are getting a spark at #2 plug.  It is just possible that you had a faulty wire and you replaced it with a brand new one that is also faulty.  You could try swapping it for a different wire (say #3) which you know is good.  Does the problem stay at #2 or does it move to #3?  If that makes no difference try swapping plugs #2 and #3.

Try all the above, and if you cannot find the fault, get back to me.