[Barry_R]

Pressure check the intake. It's a little work - but very do-able in your home garage.

You'll need to remove the rocker arm assemblies so that the valves are all closed. You'll need to remove the carb & make up a block off plate for that flange - with an 1/8NPT threaded hole in it. You'll need to plug/block off all the vacuum hoses.

Now take a common pump type radiator pressure tester and pump 10 pounds or so into the intake through the threaded port in the carb flange plate. If it leaks down some careful listening and soapy water solution will often pinpoint the location.

If the valves are leaking you'll hear it in the exhaust or crankcase & the test won't work. But if thats the case you'll be taking it apart anyways....