Bell uses these figures for mixtures
Starting 1:1-3
Idling 1:8-10
Low speed running 1:10-13
Light load ordinary running 1:14-16
Heavy load 1:12-14
The numbers for a four stroke are as follows: (again, just recommendations for baseline tuning, exact numbers also depend on other factors)
idle 14-15:1
light load/low rpm 14-16:1
light load/ordinary running 14-15:1
heavy load 12-13.5:1
On a four stroke, you can rely 100% on the afr for tuning. On a 2 stroke, the way the
exhaust works, the air in the expansion chamber can be very turbulant at certain rpm and throttle ranges. When you use an AFR in a 2 stroke you will work off the averages rather than the exact. It is a great tool to keep an eye on where you are at, it is however 1 tool out of a whole arsenal that you can use to get the bike tune dialed in.
I trust the gauge 100%, what I cannot trust is that with all the air moving and resonating around in the chamber, the readings may not be as accurate as in the 4 stroke engine. The wideband in the 2 stroke will likely not read very accurately near idle and in low throttle situations, so care must be taken to ensure proper running in those areas. You should also verify that the afr's you are seeing are corresponding with the plug readings and cylinder wash readings to make certain the bike is running as it should.It's a matter of where the sensor is placed in the exhaust stream.
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