After riding my BSA in attempt to diagnose the poor running issue the engine note change and it lost power significantly then stopped. I was then unable to feel any compression through the kick start, hence I pushed the bike home again.
On further investigation I discovered that the cylinder head gasket had a hole in it. I now suspect that the poor running of the engine was a sign of pending failure of the head gasket. At lower revs in 3rd and 4th gear while riding along there was not enough compression for the engine to function properly. Please see my earlier post titled “Losing power when in high gears” link =
There must be someone in UK, But I use Lani in USA for solid copper gaskets. He's not expensive and it's just the envelope postage each way to send yours and receive a new one....or two. Lani Visconti... coppergasketsunlimited@yahoo.com
And while I don't normally do "me too's" but I found out Lanni about 10 years ago and have been using him exclusively since then.
Lazer cut, exact gaskets that actually fit.
I scan in the head then send him the scan & he returns an exact fit gasket that works perfectly.
Not as important with a low compression WM20 but made a big difference to the B 44 & B 50.