You can get AFR autometer gauges which is what ill hope to purchase soon.

You can tell if you engine is leaning out by noticing abnormal amounts of power that your car doesnt usually possess. Also "pinging" noises are a usual indicator that you are allowing more air then fuel in your Air/Fuel Ratio.

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Honda Hannspree Edition CBR 600 RR - SOLD
Yamaha FZ1N - Purchased