did the same meself after rebuilding engine, put too much in when i changed it after running it in, but that made it smoke [lots!] at 70mph or more, keep it near the lower line on dipstick and its fine on a fast run now.
the thing is i quite like filling mr co(u)ntvertable cars up with smog when he's parked up behind me
haha! fill it to the top line on ya stick when its on a slight slope as well, like i did and you can smog out a whole stretch of dual-carriageway at 70!