Ok, I assume this is a fresh engine with a new/reground cam and resurfaced followers? Or, a good used cam running against miss-matched followers? If yes, you need to break-in the cam properly.
First:
- cam lobes and follower bases were coated with special cam/assembly lube.
- engine oil system was primed by cranking with no spark plugs at 10 second intervals until you got oil pressure.
- cooling system was filled and bled as best as possible using all the air bleeds at the rad and engine. Overfill the coolant..
- heater set to hot.
- engine static timed.
- carb rough set 1.5T out from a light seat on the idle mix and 1T on the idle speed for the stock carb.
Start the engine and immediately bring it up to 2500 rpm minimum. Don't go over 3500 rpm. Hold it there for a minimum of 10 minutes, longer preferred, up to 20 minutes. As the engine runs, monitor the warm up and bleed the cooling system as it pressurizes. Watch for leaks.
Shut down and change the engine oil and filter. Let it cool overnight. Re-torque the cylinder head and re-set the valves. Double check timing and set carb properly.
Drive normally but not to the redline and varying engine speed for 100 miles. Change the engine oil and filter.
Drive normally but only to the redline infrequently to 500 miles. Change the engine oil and filter.
Drive normally to 1000 miles. Change the engine oil and filter. Let it cool overnight. Re-torque the cylinder head and re-set the valves.
Follow regular service intervals here on in.