Ralph,


You can tell if it is a PDP, by removing the head and looking down the cylinder, at the intake ports...

PDP ported engines have two narrow, angled Louvre ports cut in the sleeve, on the exhaust side of the piston-baffle.

These ports bring fresh, cool mixture into 'hell's kitchen'...

Through the exhaust these ports are probably not visible.


I don't seem to remember whether this engine does, or does not have sub-piston induction, which may cause reverberation of intake air, potentially causing more fuel to be taken by it, as it goes back and forth through the carburettor. But mere back-pressure with no sub-piston induction, will not cause the engine to run rich.


Take that chance to see if you got an extra head shim under the head (only one is standard - two is for 10% nitro).