Just when I thought I had everything dialed in, I notice that I'm burning a reasonable amount of oil. This is from a rebuilt B20 with 20K miles, transplanted from a 72 145 and converted to carbs. I have enough paperwork from the previous owner to believe it was redone. I also have pulled the pan and looked at the bottom end and noted the new pistons, rods, etc. I haven't had the head off, but looking at the rockers seems to indicate everything was new recently as well. The previous owner did do most of the work himself, so I'm not entirely confident everything was done correctly. Engine has an overbore, and supposedly the valves were ground, with hardened seats, new guides, etc.

That said, I get the majority of the smoking at idle. It plumes to a degree that it's really embarrassing sitting in traffic. When I take off from a start, however, I get one last big plume and then it goes away entirely. I've tested for smoke by gunning the engine at various speeds and gears, but once the car is running, the smoke seems to stop, even under heavy engine load. Once I come to a stop, the smoking seems to come back after 5 seconds or so.

I would expect that a piston problem would lead to heavier smoking under load, which is why I'm thinking something with the valves. I haven't done a compression check to confirm this, but I will in short order.

I'm probably burning oil about 1 quart every 500 miles. I know it's all due to burning because while I had this engine out, I replaced every seal, cleaned, and painted it. Everything is still perfectly clean, no dripping. I am also running Mobil 1 10-40.

One of my questions is, what can I do before giving up and taking the entire head off? Can the valve seals be replaced while the head is on? Can the guides be replaced as a DIY? Is there anything else I can do to narrow down where I'm burning this oil?