When I brought my 19 plate Multi 1260 Enduro last year I was told by the vendor that it was fitted with an 'Exhaust Flap eliminator', which to be honest I had to work out what that was. I immediately realised there was some sort of minor issue with the bike, as there was a flat spot between 3500 and @4250RPM, right where the valve is doing it's bit to cut noise at the 4K test. I dug around and found a Healtech unit plugged into the loom where the valve servo should have been plugged in, which should have been a good thing, but this one had been resting on the exhaust and was melted: I brought another one expecting the issue to go away, but it had no effect at all, I took the exhaust silencer off and found the valve was fully open and the cable from the servo disconnected. Having heard about plug leads on these breaking down I replaced all 4, dropped new plugs in as well, and the flat spot got a bit better but didn't completely dissapear. I then sort of got used to it, and avoided that part of the rev range thinking perhaps the Healtech was causing it. Anyway, fast forward to Friday afternoon I was doing a little bit of tidying on the bike, had the exhaust cover off and thought, 'haven't I seen somewhere that you should wire the flap open not just leave it disconnected?' So added a lockwire to hold it open: Managed to out for a short ride this afternoon and what a difference, no flat spot at all. Obviously the exhaust gas flow at that revs was closing the valve. I'm sure everyone apart from me already knew this, but I'm now a happy bunny this evening.
Now, this is where I struggle in my comprehension. The default position for the valve is open. The servo motor, when activated, closes it by pulling on the cable. Once activation has finished the spring on the valve pulls the valve open again and resets the servo motor. It’s a strong spring. How could the exhaust flow cause it to close? Even if the exhaust flow was powerful enough to close the valve against the spring why would it become less powerful as the revs rise beyond 5000rpm such that the valve can spring open again? I suggest your flat spot is more due to the fuelling map also leaning out at the same point the valve closes ie 3500-5500rpm in order to get the bike through the then emissions tests. ESE’s are there to overcome the fact the valve invariably rusts and seizes and to trick the ECU into thinking all is hunky dory and stop it from throwing an engine management light.
Paul, Honestly, the difference wiring it open was really noticeable. I made no other changes at the same time and the flat spot I've been putting up with was gone. The spring, on mine at least, really isn't very strong at all, the disconnected valve is very easy to move with very little pressure and I doubt there is enough force in it to drag the servo motor back to it's rest position.
