"Mal Osborne" > wrote in
:

> Try a compression test. If compression is down, you need to look
> at a new motor. If it is OK, then the problem may just be valve
> stem seals. These are a little fiddly to change, but within the
> scope of most amature mechanics. It can be done without removing
> the head, but you will need to stuff several feet of sash cord
> through each spark plug hole, then turn the motor to hold the
> valves in place.

There's a gizmo you can buy or make that consists of a sparkplug shell
and a connector for an air hose. You screw it into the plug hole of
the cylinder you're working on and then connect the compressor, the air
pressure will hold the valves tightly closed while you replace the
seals.

It's worked well for me and... if you don't have a good air compressor
never mind.