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Will cam overlap affect AFR down low

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Just a question regarding cam overlap and AFR I have a vtwin motor bike with a large cam with the wideband sensors fitted into the exhaust my readings all seem accurate and on point but after riding the bike not under WOT just crusing and running around town I can pull the plugs and find the plugs to be dark/sooty showing signs of over fueling but my AFR doesnt show that could I be getting bad readings due to the large overlap from the cam or reverberation due to short exhaust? And if so is there away to adjust it to allow for accurate readings?

I am dealing with a reflash program using VE tables obviously higher up in the rev range the engine is working better and not as much pulsing compared to down low so dont have to worry about that area. The bike rides fine but just wondering about plug burn compared to AFR


Low rpm overlap. Fresh unburned charge can be pulled straight through into the exhaust. The oxy sensors measure 02, not fuel. So it will show as a false lean as it is only measuring the 02

Is there anyway to counter the overlap and stop getting false lean?

I can't immediately see an option that would work to prevent the unused oxygen showing up as a 'lean' condition unless you incorporate a catalytic converter, or somesuch, to cause the unburned fuel to react with the oxygen and use it up.

Probably the the best way would be to retard the injection start point at lower RPM, if your ECU has that option, so there is only 'fresh' air present at the inlet valve to be drawn through at overlap - might need some careful timing, though, to get the fuel into the airstream at the right time and not spray the backs of the inlets ready to be drawn through on the next cycle? It will still give a 'lean' lambda, but should give good spark plug colour and life.

If you had access to a 4/5 gas analyser, you could probably tune it using HC (hydrocarbon) and CO (carbon monoxide)?

Are you advancing the ignition timing for part throttle and/or light load operation, it is unlikely to reduce the drawn through fuel unless the above is done, but if you can use a lighter throttle for the same cruise speed, it will reduce it.

Overlap with a large cam can be a real problem and there's no easy solution. As an example, with our heavily cammed 1UZFE race engine I target 1.20 lambda at an 1800 rpm idle. There's not a particularly scientific way of establishing a target though - At idle I try varying the lambda target and as I leaned it out from 1.00 to 1.20 the idle speed picked up and the engine is noticeably crisper sounding. With reflashing a factory ECU you may be limited in what you can achieve since the lambda target for closed loop operation will always be 1.00 so you may need to force the ECU permanently into open loop mode.

The best suggestion in the cruise areas would be to try making a 5% change (leaning the AFR) and see how the engine feels. When you go too lean you won't risk damage but the engine will be hesitant and may suffer from a lean misfire.

Awesome I appreciate the answers! Thought that might be the case thank you guys

To clarify my earlier comment, monitoring HC 'should' indicate when injection timing is retarded enough to prevent fuel being passed through on overlap, monitor CO (that's monoxide, not dioxide) for fuel that isn't fully burned - you'd need to check, but I would expect

Not sure on a bike setup but on a car could you not run an aftermarket wide band gauge like Innovate and then run the output form this to the factory ECU and then bend the curve to give a lambda 1 output when the car was actually lean. Although not sure if you can change this to RPM etc so t may effect things over your entire fuel map

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