Hi Colin 725,
Sorry to hear the new acquisition has a few frustrations - and all the preceding advice is a very good place to start. I'm in Richmond, so not too far from you; although mine is a +8 of similar vintage, rather than a +4, you are very welcome to head up here and I can both give you a run in mine (which I believe behaves pretty much as Morgans of that age should do) and I'm happy to passenger yours and give you my views. Alternatively, there must be close/closer +4 owners who will be happy to extend the same offer to you.
PM me if you want to fix something up!
Dave