Found these small tachometer quite handy for checking the RPM: idlle speed, shifting, max rpm... Run on battery, last a couple year, no hard wiring, just need to wrap the pickup wire few turns around the spark plug wire. You can get them for about $5.00 USD online Free Shipping (if you don't mind waiting few weeks)
We use similar China strap-ons quite a bit. Accurate and cheap. Ugly but functional. In the good 'ole USA, you could pay TrailTech a whole lot more...and get the same thing.