However it's worth pointing out that if the carbs are in fact jetted too rich, introducing a lot more air by removing the filter can give a 'mixed message:' if the plugs clean up after removing the air filter element, it can mean the filter is clogged -or- prove that it's jetted rich (stops running rich due to lots more air coming in) If introducing more air by removing the filter cleans up the plugs, it is not necessarily conclusive. But I'm gonna try it.
It is a common misconception that the stock air filters limit air flow. While true, to an extent, at the very high air velocities found at and above red line, if your engine is able to achieve red line, then the air filter is NOT denying air at mid range and certainly not at idle where the air flows are far far less. The stock Honda filter passes more than enough air volume at red line for the stock engine. (Possibly not above red line, though).
The filter is a membrane. As such it presents a pressure change across it while air is flowing through it. A filter with more restriction creates a higher pressure drop across it. The pressure drop in the carb throats, whether caused by the piston fall, or the venturi effect in carb throats, is further offset by the pressure drop across the air filter. It is the throat pressure in the carbs relative to the outside ambient pressure that determines the flow rate through a given size fuel jet. The greater the pressure, the more fuel flows through the jet, even if the exact same amount of air is flowing through the carb throats.
Given the same venturi size and the same engine mechanical efficiency, the filter makes little difference in the VOLUME of air getting to the cylinders (air speeds below red line operation).
The graph below demonstrates how paper filters behave regarding pressure drop across them.
The vertical graph axis is the pressure drop across the filter. The bottom axis is the number of filter cycles in a closed loop test of the membrane.
The Bottom A line is the base filter pressure differential when no particulates are introduced (or so little as to not effect the pressure drop, as in a way oversize filter cross section).
The B line is where enough particulates are introduced to effect a pressure drop change. The number of passes through the filter reduces the available air passageways and thus increases the pressure drop across the membrane with each pass of the contaminated air.
Only the A line is assumed for ideal jet size selection. That way, when a new filter is installed, the jetting is returned to the correct value.
Unless the trapped particulates are day glow or luminescent, you will not see the microscopic particles blocking some of the airways through a paper filter. Also, you can't see if the paper fibers have sagged/distorted to close up the pores. And, you will certainly not be able to see what sort of pressure drop across the membrane exists without some instrumentation both before and after the membrane position in the air duct.
Don't feel bad about getting this wrong and buying into the myth vs fact. Many here have stated that since pod filters require a jet change (bigger) to run well, they make the erroneous assumption that the filters must some how deliver more air to the engine. This is quite false, as the pod filter only changes the carb throat pressure via a filter membrane change and the shortening of the intake duct tract (raising the pressure closer to atmospheric levels). This makes the original jets flow less fuel. They are fooling themselves (and any others that believe the myth), much to the delight of pod filter salesmen and marketeers.
Cheers,
