My engine has about 450 hrs. (new in 2018) I use Unleaded 98 fuel. I normally cruise at about 4,150 - 4,300 rpm. I have been getting a slight vibration/change in engine noise (best described as bzzzz) but no change in power mostly in these instances:
1) when reducing power.
2) running under 4,000 rpm
I first noticed it at about 200 hrs. was very occasional then. Progressively increasing in frequency and duration. I did have a prop strike at low rpm just prior to 200hrs and engine was checked deemed to be ok.
Previously it would occur for a couple of seconds, it will stop if I increase RPM.
My last service at 400 hrs (this year) did a full carby service and balance and checked ignition coils. The sensation still occurs and has been getting more pronounced and lasting longer now possibly around the 10 -20 seconds at a time or until I change RPM.
I have notice it to be random in duration a typical example is: bzzzzzzzzzzzz ...............bzzzz.......bzzzzzzzzzz. ......bzzzzzzzzzzzzzzzz
Initial thoughts were to consider the coils or carby doing something hence the full carby service and balance. . Now I am thinking gearbox after reviewing some of the videos on this site.
Any suggestions please?
