Clearance on a coated ProX piston?

[DesmoDrew]

You think taking a die grinder and carefully making the head gasket hole bigger is the way to fix them?

   That is a perfect solution. 

[pidjones]

I'd suggest a sharp knife. If using a Dremel, I'd use a burr. Dangerous to grind nonferrous with a stone.

[DesmoDrew]

Dangerous to grind nonferrous with a stone.

   What makes it "Dangerous"    Stones load up=PIA.  And of course proper ventilation, hearing, breathing, and eye protection are Strongly recommended.  But for this particular solution/application (what this post is about) the only 'danger' is knocking over your beer. 

[1976RD400C]

I used a rotary carbide burr cutter in an air powered die grinder. It cut like butter but had to be careful I held it at a right angle because it could catch and throw the gasket. Head gaskets have a 64.75mm hole which make it hang over into the bore quite a bit with 65.25mm pistons.   

[1976RD400C]

ProXs are all broken in and all seems ok. First run out it ran kind of flat, was not accelerating as hard as before. It didn't have the power it used to. I checked the plugs and they were richer than it has ever been. Messing with these carbs for 10 years I kind of figured it was needle height problem. Lowered the needle and oh yes. That needle circuit has to be right or you are missing out on a lot of performance.