After all the seals have been replaced and the carby is correct, then the only thing left is the dreaded bottom seal. I've had a couple (maybe 4 or 5) out of the hundreds i've repaired where the bottom seal is the culprit. If this is the case then a complete tear down is required to replace the bottom bearing and seal. If you're going to that effort, then a complete once over is recommended, both bearings, a light hone and new rings at a minimum.
