CV 40 Issue

[fourthgear]

  A Friends Panhead was running real bad , long story short . CV 40 ,VOS Port Plug , was gone , found it wedged between the Intake Manifold & Front Cylinder. This motor got kinda warm ,both Head Gaskets were blown, the Carb is dirty with what looks like soot , & what I started this Thread for , the Vacuum Piston has what looks like it had a spark plug firing on it , the Plastic has some minor or slight melting going on where the Diaphragm & Piston meet. This marking is opposite the port passage for that VOS Port Barb , what is getting so hot to make it look like a fire is going on in there . The Intake Manifold is clean as a whistle , there is a K&N filter on this motor , but its been on for years & never looked like this , nor has there been any thing on that Vacuum Piston .

I'm pretty sure it had something to do with the very lean condition , just odd to me .

  Any thoughts or experiences , I'm not all that familiar with this type of carb.