And there's no issue with idling? - and the speedometer still works? The maintenance manual shows how to troubleshoot this circuit but doesn't give a whole lot of theory on how it works.

I'm just stumped at why the engine runs fine with the speedometer DISCONNECTED.

The main connector that comes off the speedometer goes into what looks to be a relay - I assume this is what controls the solenoid at the air box.

 

I rode mine with no plastic for a while and took out all the hoses going to the front vents under the headlight and bypassed the solenoid and have had no issues at all. (speedo fine, Under 15mph no change) The whole system is just there for emissions reasons. Ive heard of grounding the wire. But it only takes a second to just bypass/remove it. Not quite sure if this helps but didnt really understand exactly what you were asking.

 

Why wouldn't it? The ECU probably has no input for speed. Unless you refer to the air valve business in which case I guess we will never really know why it's there as the bike runs fine with direct "fast" plumbing. Maybe as suggested it's some emissions thing. The only bikes I've heard of (in Europe) having some sort of speed sensor for engine management are those that might exceed 300Kph (186mph?) which are speed limited because the Japs are scared of waking up the legislators. Lots of litre+ bikes have ignition retard in the lower gears to help keep riders sunny side up - as they are capable of easily hoisting the front without clutch help you can't use full power in the lower gears anyway. That was why the 2004 ZX10 was a fearsome beast, it had no limiting in the lower gears apparently.

 

Let's see if i can beat this thread to death more than it already has - and I do appreciate the feedback you guys have offered.

WHat I'm trying to wrap my head around is the failure mode of this sensor (being the typical aircraft avionics guy that I am). When the sensor gets a voltage from the speedometer (at speeds over 12MPH) the ram air source switches from the small intakes to the large scoop inlet, offering the engine more breath. But what happens when the system fails? It never switches, obviously. But why, in the case of my bike, when the speedometer is disconnected, does the engine run fine? This would seem opposite. Without the speedometer input, the system should be STUCK in reduced air input mode - and not run correctly because it's starved for air.

 

I think I remember reading that it would work fine without the speedo Meaning failure mode would be open to the main ram air at all times with it disconnected. I cant tell you from personal experience because I took the speedo off at the same time i removed the solenoid. It only closes when you start the bike W/speedo and then opens or turns OFF at 12mph I think this is right.

 

Another success story here. Rerouted induction lines bypassing the solenoid....problem solved. Runs like an F3 again.

Hugely valuable thread this has been.

Now if I can only find a used headlamp........

 

wow, i just had the same issue and doig this mod fixed everything!!..SO HAPPY RIGHT NOW!

 

now did all F3s come with this?... the hoses on mine look like a jumbled mess on mine, and i have extra hoses in a box... i bought another OEM box w/ a K&N in it... but where would the flapper thing be at? (seeing as the bike is still apart)

 

Not sure what you mean by "FLAPPER THING". If you are talking about this air solenoid, it's ellectro-mechanical and it switches air flow to the engine (air box) between the small and large air intake hoses on the front of the motorcycle, depending on speed. I'm pretty sure this pressurized air induction system was Honda's so-called improvement when the 95' F3 was intro'd but i may be wrong on the year. Get a service manual for your year and you'll see it.

In any case, the solenoid should be below and slightly aft of the fuel tank and if you follow the air tubes that route down the side of the frame you'll get to the solenoid that's either been bypassed or still connected.

Look at the very clear pictorial early in this thread - it's spot on as to what you'll see and what to do.

 

You assume that with no signal the solenoid is on slow - that is just an assumption and not necessarily true. It could be the other way round. I make this up by the way so test it to see; it might be fast on low voltage and when you switch on it goes high, then low over 12mph.