Wax-Fast idle valve.

Does anyone know how it increases the idle? It moves with coolant temp. but does it open throttle plates or is it an air bleed into intake. Controlled vacuum leak?

Good question and I don't know the answer for the Swing.

I do know that on my ST1300 and the VFR800 the wax unit bears on a plate that lifts the starter valves open; the starter valves are an air bypass path around the butterflies. The idle adjust screw on those bikes also bears on the same lifting plate.

When cold, the SVs are opened by the wax unit and and when hot the wax unit moves far enough that the SV plate position is now fixed by the ide adjust screw; the only thing that moves the throttle butterflies is the throttle cable and as far as know the butterflies are fully closed at rest/idle.

I assume the Swing is conceptually similar but the TBs are very compact so it is hard to say. Certainly the wax unit bears on the area where the SVs are located so I assume the wax unit is either driving these open or the wax unit operates another separate bypass (which seems less likely).

The SVs on the Swing are a bit different in having adjustments for both SVs, the other bikes all have a fixed SV and the other 3 are adjustable to synch the vacuum to the fixed one. I'm not sure what that implies.

Actually, looking at on-line images of the TBs suggest that the idle screw and wax unit work together but the balancing screws are separate to this. The idle/wax are in-line and look to be fed through a fairly large central port (1cm?) where the balancing screws are fed through a pair of much smaller ports. I note the manual also refers to the two screws as "Air Screws" not "starter valves" suggesting they are fixed and not moving open.

Given the physical look of the idle screw on the parts fiche it does not appear to have any sealing mechanism (e.g. an o-ring on the end of the spring) so maybe this and the wax unit do indeed work on the throttle butterfly shaft between the bores. Certainly the orientation of the idle screw is correct to limit the closing travel of the throttle shaft (which would push up against the idle screw) and the wax unit would be correct to push the butterflies open for fast idle.

I do know that on my ST1300 and the VFR800 the wax unit bears on a plate that lifts the starter valves open; the starter valves are an air bypass path around the butterflies. The idle adjust screw on those bikes also bears on the same lifting plate.

Air bypass then. I'd say Honda would most likely uses the same type bypass on SW. Many bikes have none fixed SVs bleeds but must follow service manual to synchronize throttle bodies. Good info. Thanks.

AHHH you reposted while I was answering. Air screws are bleeds in throttle bodies . Wax valve is centered near idle adjustment screw. Another night and more thoughts. Bed time.

I'd love to have a throttle body to dissect! But my current best guess is the wax unit and idle screw adjust the throttle plate position. And the air screws provide a bypass path to balance the vacuum and (maybe) also provide a basic idle speed even with the throttle plates fully closed.

It should be reasonably easy to see if the throttle cable drum is moving closed as the temperature increases from cold. Maybe I'll try that tonight.

OK I checked that. There is a non-user accessible throttle stop on the drum, so the idle screw and fast idle are independent of the butterflies. Must be another air bypass system.

All or most throttle bodies or carbs. have a fixed throttle stop. Plates can get stuck at closed position from engine vacuum or spring pressure. Plates bind against throttle body. Stop holds them open a bit.

I looked a several throttle bodies on Ebay and still can't see how it works. Part in hand would solve the issue easily.

I was thinking that the idle screw and wax unit may have acted as a throttle stop and move the butterflies a little. I that was the case, when cold the wax unit would be holding the throttle off the fixed throttle stop, but that is definitely not the case. The idle screw and wax unit must be acting together on another bypass circuit I think, but I can't imagine how that works.

Just bringing this thread back from the dead!

I came across the linked document today, and it describes in some detail the different FI systems that Honda have used in the same time period as the Silverwing. The twin cylinder VTX1800 setup looks conceptually similar to the Silverwing (albeit aligned for a big v-twin not a little parallel twin beastie. Interesting that the idle speed adjuster acts on a ramp on the FIWU; I had not pictured that before.
http://www.damet.com.pl/pub/moto/gl/GL1800.-.Programmabale.Fuel.Injection.2006.pdf