A gastester is an essential part of doing tuning to carburetors or fuel injection. I’ve been using the Gunson Gastester to tune both my own and customer bikes for 10 years. It is the least expensive O2 sensor on the market. The sensor works with a probe that slides into the exhaust pipe. Simply attach the electrical leads to the bike’s battery, let the Gastester establish a baseline reading, set the reading to 2.0 (normal atmospheric CO levels are 2.0), warm up the bike and insert the probe. A few minutes of tuning are all that is needed to optimize the carburetion/injection fuel ratio. On injected bikes, I use the Gastester in conjunction with tuning software for tuning all injection systems on Ducatis. See my maintenance guide for sources of software.
Instruction Sheet included.
NOTE 1: The last time I stocked out of these, it took 5 months to get another shipment. You snooze, you might lose.