Just a thought, could it be the age old Morgan problem of fumes getting into the cabin?
I’ve had 4 different Morgans and they have all done it, the latest CX Plus Four being the worst of the lot!
Get the engine warm then bury the throttle, when you have reached a decent speed lift of the throttle totally, you will get a good whiff of Shells finest and it does actually smell a little like you describe.

Sir P