Knucklehead plug issues

[PSANTORA]

I pulled the carb and re-installed the test apparatus. Got good results with no leakage at the manifol nuts but got bubbles coming from around both plugs with the worst of the 2 being the rear plug. I increased the air pressure from 15 to 20 and got a lot of bubbles from the rear plug. My first question is whether it's okay for that air to get by the intake valves when they are both closed and what to do to correct the leak at the plug area.

[T. Cotten]

Phil!

We now know WD-40 testing is futile.

Please inspect the plug counterbores where the crushwashers seat for any blemishes.
They may require spot-facing, or perhaps you can just use more compliant washers.

The intakes will begin to crack open at higher pressures, but fifteen psi is already overkill;
the motor can be turned to where it opens and pressurizes the combustion chamber, so that the plug and headgasket can be "snooped" with soapy water.

It doesn't hurt to wet down the entire head around the intake ports, to detect any micro porosities.
Last spring I found one that leaked past the guide in the head to bubble beneath the valve tin!


....Cotten