I'm in a fix with my 1970 Amazon (B20), regarding smoke from the tail-pipe. The PO put on a larger valve head (44mm) when he had an unleaded head replacement about 2 years ago, and a thicker gasket to raise the compression. It has A cam with a single stromberg.

Had an oil change at my shop (Volvo place - they know what they're doing), then left the car sitting for a few days. First start up produced huge clouds of smoke which came out of the tail-pipe for about 30 seconds. Smoke died away once I was moving, but came back (less but noticeable) when I deliberately did engine-braking at speed. No smoke at acceleration.

When the car is stopped and restarted only 4-5 hours later it starts cleanly.

From reading about this, some culprits seem to be piston-rings, valve-guides, valve stem-seals. But I'm not sure which of these can be diagnosed without taking the engine out? It will cost me about $600 just for someone to take out the engine and put it back, so I want to avoid this if possible. Is it also possible that too much oil at change-time would aggrevate the problem? I've read on other forums people taking out 200ml and the problem is almost gone.

Shame, because the car's in great condition and I paid a lot for it.

Thanks as ever for advice to help me plan what to do with the car.

TomTom