Hey Carl,
Your guess is as good as mine. Really not sure whether it's #5 or #6 just here a periodic knock from the top of one of the two rear cylinders. This just started yesterday along with the popping from the exhaust after I adjusted the valves. Darn thing sounds like a bag of popcorn in the microwave just about ready to eat. Any ideas? Valve lash too tight causing the valves not to seat completely closed. Ran fine before I started making the adjustments. Only made the adjustments because I noticed #4 intake was way too tight.
