MF, I would suggest you get a little tachometer like this one https://www.ebay.com.au/itm/Digital-Engine-Tach-Tachometer-Hour-Meter-Inductive-for-Motorcycle-Motor-SE/143310228155?epid=7020916288&hash=item215df48abb:g:~wEAAOSwHNxaCVIC .
If you get one like that, I suggest checking they mention a CR2450 battery not included - otherwise you have a sealed battery that isn't replaceable
The rusty corvette sounded like it was over revving, but tach measured it at 3500 rpm.
