Not a mechanic. Bought 66 Mustang that was running but real rough, no power. Changed Cam, Headers and distributor to HEI. NewCarb 500. Electric fule pump. Started for Break-in. Easy start, but it boils the coolant. The reserve tank shot open and was boiling for ten minutes after high RPMs for the break-in and for ten minutes after high RPM. WTF? Appreciate any insights.