Did you change the valve stem seals?

Have you checked your bottom end? sounds like maybe rings are worn?

Easiest way to check is to take the crank case breather off the back of the rocker cover but stick your thumb over the end of the pipe you remove [or the engine'll cut out ]

If there's white gas coming out the hole, you got a crankcase issue and its quite likely the piston rings are worn and you're getting some blow by, but worst case block/bores need attention.