This is not always a good thing since there is effectively less surface area gripping the insert, but isn't a problem if correctly fitted. I also advise a small before Winter check to prepare the car for storage. Just add the recommended dose with every tank full. Even in the subaru of Bernie's friend a fuel of the same octane rating as the one it has been set up on will make it run just as well. I generally use the genuine Rover types, as they are pretty cheap and small in outside diameter and depth whilst having a larger inside diameter. Modified cams will need modified distributors to suit. A vehicle that's done over 40, miles on leaded fuel will probably do 10, miles on unleaded before problems occur.
MG Midget and Sprite Technical Lead additive in unleaded engine? BBS discussion at MG-Cars.net
Before we get into the problems and the possible solutions, we should take a look at "leaded" gasoline and see just what the "lead" was supposed to do. Some of them have been experimenting with additive enhanced fuels. At worst, I might have needed to redo valves, guides and seats but you can do a lot of miles before that is necessary. RON is a somewhat misunderstood issue as using a higher RON fuel won't necessarily deliver better performance. You're the highest bidder on this item. There is some confusion, too, as the V8 was reputed to be suited for unleaded whereas the B wasn't.
Unleaded vs. Leaded fuel? : MG Midget Forum : MG Experience Forums : The MG Experience
But do check that the ignition timing is correct - not necessarily to retard it a bit, but just as you would with any engine. He had a problem with seized guides. If none is heard then advance by a degree at a time until it is heard and then back off one degree. My experience is simply to let the engine idle for about seconds to cool down and then switch off, and if necessary load up the engine by engaging the clutch as you switch off.
MG Midget and Sprite Technical Leaded Cylinder Head BBS discussion at MG-Cars.net
Description: To increase your chances of winning, try raising your bid. The point being that timing is reset according to the fuel's RON, and thus with a head designed for leaded, whilst the car will run reasonably well on std unleaded when properly timed, it may not perform as well as being re-timed and fed higher Octane. Suitable exhaust seat inserts fitted into the cylinder head are a minimum. These guides can seize if not reamed to provide adequate clearance, particularly on the exhaust side.