better running rich than lean on these engines. Things can go pop if running lean
Problem with running too rich is petrol dilution of the oil that can lead to pre-ignition and less protection for the cylinder walls.
Think you are trying to describe "bore wash" which would only happen if the engine is running very rich such as 9:1 afr. Bore wash and oil being diluted by petrol wont cause pre-ignition. Main cause for bore wash is people flooding their engine trying to start it, not common with modern engines.
Revo settings cant show how rich/lean an engine is running, this can only be measured by analysing the exhausted gasses to see the ratio of oxygen vs unburned fuel.
Then you need to take EGT (exhaust gas temp) into account, this is a far more important factor than AFR. Your AFR may be 11.5:1 under load but EGT may be high so you would richen the fuelling to bring the AFR and EGT down.
Then there is ignition advance, this will alter EGT and AFR. The earlier you ignite the inlet charge (the more advanced your ignition is) in the combustion cycle, the more complete burn you should get. So if you have rich AFR's you can actually get these to appear leaner by adding ignition advance. Add too much advance and you ignite the inlet charge as the piston is still travelling up the bore, crank is pushing it up, combustion is pushing it down, piston has nowhere to go so it rattles from side to side against the walls of the bore and causes 'knock' which is detected by the knock sensors and the ecu removes the timing advance to a safer level. If your timing is too late you will not get a complete burn and less power is made, the combustion happens when the piston is on its way back down the bore and you have missed the window of opportuninty to push that piston down with the force of the combustion. This also raises EGT's.
So when you see someone post their Revo settings online and they have a fuelling of 4, this actually means very little in the context of how rich or lean the engine is running.
