Ralph,


What fuel are you trying to run this engine on?

It is a high compression engine and is designed to use 0-5% nitro; not like many current engine targeted for North America, that will run on 15% nitro.


This engine will simply not tolerate much nitro.


Also, there was more than one version of the Blue-Head ST; the earlier baffle-piston type and the Schnürle type.
The two can easily be distinguished by looking at the external design.

The older baffle-piston type also had a PDP version, which made as much power as the Schnürle type.
I believe there was also a two-plug version...

What type is yours?


As to the raw fuel leaking from the front (runny nose), it could be your crankshaft is highly corroded in the front-rotor area (under the carburettor), where it is supposed to seal.
Leaking there is a symptom; not the real problem.


As to your concern from the small entry hole to the Macs One-Piece (I presume)... have you seen how small the entry is to an UltraThrust tuned muffler, for an OS .40-.55?
I believe it is about half the area of the engine's exhaust stack.

Also, it will not affect the fuel pressure (causing a rich condition), since it is up-river from the muffler. What could affect fuel pressure is a small outlet hole from the muffler.