Maybe some basics will help.
The carbs react to the piston going down on the intake stroke, which draws a vacuum in the intake runner all the way from the cylinder valve to the point at which air is drawn from the atmosphere. (Since you have pods, that would be the filter's outside face. (If you had an air box, it would be the air box inlet opening.)
The depth of the vacuum created in that intake runner is effected by the resistance to air flow between those two points. If you block the inlet in some way, the depth of vacuum increases along the entire runner length. Similarly, just changing any restrictive element along the path also changes the specific vacuum pressure presented to the runner walls along its length.
The vacuum pressure is important because lower pressure in the carb throat is what draws fuel out of the carb bowl through the fuel metering jets. (For casual readers, yes there is the venturi effect too, but this hasn't changed on the subject of this thread.)
Anyway of you change the inlet restriction characteristics, this in turn effects the volume of fuel that will pass through a given size metering jet orifice. Honda engineers selected the fuel metering orifice size for the vacuum that occurs with the
stock air box, filter, engine breathing characteristics, and the exhaust back pressure. Popular folk lore has it that the air box and filter were a huge mistake for various reasons other the engineering principles, so this device is often discarded, and cheap pod filters are installed in its place.
Pod filters reduce the inlet restriction, leading to reduced carb throat vacuum, leading to less fuel being drawn through the metering jets. Since the engine mechanicals have not been changed as well, the air being drawn through the inlet has NOT changed in volume and if you deliver less fuel for the same volume of air to the cylinder, the engine runs lean. Standard carburettors do not have any means to self adjust their air fuel ratios with changes to
stock air box, filter, engine breathing characteristics, or the exhaust back pressure. So, the carbs must be retuned for these changes. If the vacuum pressure depth has lessened, then the fuel metering orifices must be increased in size to restore the proper air/fuel mixture in the combustion chamber. The common folk lore that larger jet sizes means you a making more power, is simply false, btw.
Your mechanical slide carbs have three prominent and adjustable fuel metering devices that must be addressed when changing the
stock air box, filter, engine breathing characteristics, or the exhaust back pressure. These are the Slow/Idle/Pilot circuit which dominates at throttle positions from idle setting to about 1/4 throttle, the Throttle valve (slide and slide needle), which dominates the fuel mixture between 1/4 and 3/4 throttle, and the main jet which dominates between 3/4 and Wide Open Throttle (WOT).
It is possible to overcompensate any or all of these carb settings/adjustments. The result is that fuel hydrocarbons that can't find oxygen molecules to pair with, get deposited on the combustion chamber walls in which the spark plug tips protrude. This looks like soot, is electrically conductive and when it coats the sparks plug's center electrode insulator, it shunts the spark energy away from making an arc across the electrodes.
How to correctly retune...
The goal is to supply the proper ratio of fuel to air at any throttle setting. When this occurs, best power is available from the engine, and there are little or no deposits left on the spark plug bits that are in the combustion chamber. The heat from correct ratio burning self cleans the spark plugs.
Modern techniques employ a dynomometer, which allows the engine to produce its maximum power at any throttle setting, along with instrumentation to "sniff" the exhaust so that the air fuel ratio can be mapped over the entire throttle setting range. This technique replaces some tuning skill with science, and is probably the fastest way to readjust after changes to the stock configured machine.
The "home brew way" is to find a test track, and force the engine to make maximum power, and then look at tel-tale signs of combustion remnants deposited on the spark plugs. This is affectionately termed the "Plug chop" method. To freeze the moment of chamber conditions, the engine is run under load for a sufficient period of time to produce plug deposits, then the engine is stopped as quickly as possible, the spark plugs are pulled, and the deposits "read" for combustion conditions.
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.htmlSince the main jet has the largest orifice and also feeds the throttle valve, this jet is usually selected first in order to produce clean spark plug deposits, and best distance/time numbers on the test track.
Then the throttle valve (slide needles) are set using midrange throttle settings on the test track, so that the spark plugs don't build up excessive deposits, brown to tan is good, as it should be slightly rich for acceptable throttle response in this range. (assuming your don't have an accelerator pump).
(Be aware that the needle taper profile also sets 1/3 and 2/3 throttle settings, if the taper is wrong, 1/2 throttle can be correct, but the 1/3 or 2/3 throttle settings can be either rich or lean)
Finally, the idle air bleed is adjusted for as lean a setting possible, yet still allow the engine to respond for brisk power when given up to one half total throttle travel on an instant twist.
All this tuning will be a total waste of time unless all the carb internal parts are clean and undamaged.
When this is all accomplished, you have successfully adapted pod filters to your bike. And, future owners of the machine will thank you instead of curse you.
Is this of any help?
