I had made a few post about this. I was getting what sounded like a pinging issue at about 4000rpm. You would mainly hear it at about 70mph in 5th (which is about 400rpm), but it you could also hear it in 3rd and 4th at 4000rpm.
So after trying everything I could think of as well as all the suggestions. I may have found the issue.
I had MAC Whispertones on it all this time. Recently I remembered my Eldo 850 didn't really like them until I rejetted the carb a touch. I had a crusty looking pair of MAC Slashcuts on my shelf that I know my 850 ran perfectly with until I removed them. Installed those and now the noise is about 75% or more gone. Now at 70mph is finally fairly quiet. If I am going up a rise, I can slightly hear the noise, but is way way better then before. It was constant at 70mph+. It also now seems to effortlessly want to run at 75mph and about 1/4 turn of the throttle. Before it seemed labored to go over 70mph, would do it, but almost half a turn of throttle.
Next I will try another set of roached out mufflers that have a crossover. When my Ambo was a 750, it did not like mufflers without a crossover. Maybe the 1000 wants a crossover as well?? Next to try on my list!!
Thanks again for all the suggestions!!!!!