For the very first time, I am having an (B20) engine problem with the beautiful 544 I bought four or five years ago. Until last month it ran like an old reliable - never a problem. Now, after a month in the ice cold garage without being driven, (once it gets warmed up) if I go to drive it, it shoots out loud gun-shot-like backfires and it is sluggish if it moves at all.
The gas in the tank is from last summer with a little lead substitute in there. I get different theories from different people. (Not having tweaked the engine since the last time I drove it, I am mystified.) I put a little WD-40 spray inside the distributor cap to keep out moisture and I added a little additive (alcohol-based) to the gas tank to remove moisture, but it did not fix the problem. I heard the theory that it is a timing adjustment problem or a carburator issue.

Any thoughts as to the correct diagnosis? If the countermeasure is involved, I'll probably wait for warm weather. I'm afraid of doing more harm than good by fooling with the distributor or yanking chains...
Thanks....