I also had the car 'converted' to using unleaded petrol (i.e. new valve seats).

It was giving me problems with 'pinking' and 'running on'. Research showed me (eventually) that regular unleaded petrol, here in Australia, was only 91 octane (as we said in the 'old' days). MGB's run on 98 octane petrol (assuming the are high compression ration, which mine is, viz. 8.8 : 1).

So I took the plunge and filled up with what is here known as BP Ultimate. This is lead-free but is 98 octane. (You can check on the Web local retailers of such fuel).

Results: No more 'pinking'. No more 'running on'. Better performance.

Of course you might know all this but it took me ages to find this information, which is why I am sharing it.

Advice/notes to owners of these beautiful cars:

• Have your valve seats renewed for unleaded petrol.
• Use 98 octane (unleaded) petrol, whatever you need to pay for it.
• Resist buying cheaper petrol and adding additives (they are not always compatible should you get stuck for your particular brand). In the long run, they'll cost you more and the thought of adding them at 1.00 in the morning on a lonely Motorway with the wind blowing sleet across the lanes of wet highway, is not a thought I would want to endure.
• I am using a slightly colder plug than N9-Y's. I'm using Bosch W7DC plugs. I'm not sure if that makes much difference but it can't do any harm that I am aware of. Spark-gap should remain at 25thou (0.0625mm). No sense in changing that.
• With these modifications have your car re-tuned if necessary.
• The cost of renewing valve seats/ extra cost of petrol is invaluable when you consider the damage done to the engine in the long run (that's a pun).

Made in England