squirt oil or starter fluid or wd 40 around all parts that can cause an air leak,intake manifold, base of carb, if engines speeds up or runs smoother at any place you sprayed you have found the leak, use hardwood for the spacer, any thing hard will just let the heat travel thru it to the carb, the thicker the better, at least 1/2 inch or better ,aluminum is the worst for heat transfer