MSefi.com read only forum (Jan.15,2018)

I'm just wondering if there is any reason the Honda automatic fast idle system would be a problem with tuning MS-II? It uses the coolant temperature and engine vacuum to operate, with an in and out plumbed directly out of the coolant system thermostat housing. As soon as the thermostat opens it allows the warm coolant to flow through the fast idle valve (WAX), which switches off using the engine vacuum to power the mechanical actuator.

Please disregard my previous explanation of the WAX units operation which is posted above. Below is a detailed explanation of how it operates.

The Honda WAX unit found on many of Honda's fuel injected engines is an actuator that opens small air bypass passages that effectively allow extra air to be fed into the throttle body. A lot of engines have a powered mechanical actuator (IAC) which is controlled by the engine ECU. The WAX valve fitted to Honda TBs is effectively automatic, and operates through the expansion and contraction of a heat sensitive "wax" which acts upon a piston inside the WAX valve. The wax shrinks inside the valve when it returns to room temperature, and as it shrinks it moves the piston inwards, opening the air bypass valve. The WAX unit has a coolant inlet and outlet which are connected directly to the engines thermostat body and coolant system. When the thermostat is heated by the hot coolant and opens, the hot coolant flows through separate lines that run to and from the WAX unit and subsequently the coolant heats the wax, causing it to expand and move the piston outwards, this in turn closes the TBs bypass air valves, and subsequently the engine returns to it's standard idle speed.

Hopefully this help anybody doing a search, or like me are fitting Honda motorcycle throttle bodies to a previously carbed engine. The good news is that the WAX unit frees up MS resources, and is one less thing to worry about when starting up for the first time... hopefully!