Prompted by John Parker's request for problem solvers, this is my solution for hot carbys. I machined a shallow groove on each side of the insulating spacer to take a 1/8inch viton O-ring sitting slightly proud of the spacer to be compressed/squeezed into the groove & against the barrel on one side & the carby flange on the other side to give a air tight seal. No other gasket is required. You do of course have to make longer studs to suit. My bike is 600cc & running Goldie touring cams & in Queensland (OZ) with summer temps of 30plus I have had no problems over a couple of years. I pulled it down recently & could have used the O-rings again but hang the expense, new ones went in.