I have an annoying downshifting problem. When slowing and gearing down the revs hang momentarily and make the downshift from 4th to 3rd very difficult until the rpm drops and gearbox is unloaded. Happens with throttle released, clutch pulled at 2500pm and bike slowing. Revs stay there for a short time before dropping down. Only seems to happen in 4th to 3rd downshift.
Clutch cable is adjusted to spec, throttle cable adjusted to spec, throttle position sensor has been reset. No ecu error codes and I can hear the iacv making operating noises when tested but don't know if it is actually doing what it is supposed to be doing.
If I downshift 4th to 3rd at higher rpm it doesn't happen, revs drop immediately when clutch pulled and no gear change resistance, drops right into gear.
I've read that he iacv adjusts not just idle rpm but also affects low rpm range as well. Is this right?
Location: St.Leonards on sea, East Sussex, England.
Posts: 1,260
What's an IACV?
Tick over revs are set within the ECU. If your bike has developed an air leak on the inlet side, that might affect the revs like that. Certainly does with a carbed bike.
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H
'02 Tiger955i in black.
Last edited by blacktiger : 02-29-2008 at 03:09 PM.
I find downshifts a bit slow and baulky on my 06 under the conditions you describe. Like you, I've made sure that everything is adjusted properly and recently changed the oil.
I feel that the clutch drags slightly and may improve as the plates wear more. Although the gearbox is positive and doesn't have false neutrals. It's not the best for fast changes.
What's an IACV?
Tick over revs are set within the ECU.
Inlet Air Control Valve. In most EFI engines, the throttle butterflies close completely when you close the twistgrip. The ECU then uses the IACV (sometimes called a stepper motor) to bleed more or less air in behind the butterflies to control the idle speed. In other words, unlike a carbed engine, idle speed isn't controlled by the throttle stops.
I assume this is what the Triumph engine does although I haven't seen it documented as such.
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Ian
2004 Tiger 955i
1955 Velocette Viper.
Pickaxe, yes it could also be sticky dragging clutch plates. I was thinking of doing something similar to what I had to do on a previous bike when clutch stuck badly after an oil change. Front wheel against wall, rear brake applied, out of gear, clutch pulled, then hit the starter, but slip it more in gear. I wouldn't think a little bit of clutch slipping should do any damage, this is what they are made to do right? My riding is mostly highway commuting and it only takes a few minutes to get out of town so the clutch has seen proportionally very little use so far.
Iansody, your description of IACV operation is what I have seen also. Like you I have not seen Tiger specific documentation though. Still waiting for my shop manual to arrive but thought I should try everything else before pulling the tank and airbox to get at it.
As far as adapting to it I try to downshift earlier at higher rpm and it doesn't have this problem.
A lot of people rag on Harley riders for revving their engines on the downshift, much like a double clutching in a non synchro car gearbox. There is a reason for it, and it's quite simply to make it easier to a) get into the lower gear and b) make it easier on the drive system.
In case, for those who don't know how. Pull clutch in, and at the same time, in one fluid movement, rev the engine slightly and click down the gear shift. This helps to bring the engine revs up to the right speed for the new gear and allows the engine to do the slowing rather than the clutch and gearbox. Hard to describe in print, but this gives you the idea...
and will save you any worries about clunky downshifting and dragging clutches.
All those who grew up on Nortons and Triumphs etc do this as a matter of course. It always makes me wince when I hear someone clunking down the box without.
Mind you, the box on my Commando was much nicer than any modern gearchange I've tried. Never a clunk going into first, and changes in both directions as smooth as silk.
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Ian
2004 Tiger 955i
1955 Velocette Viper.
Well, its now been diagnosed but not cured. It was not the IACV or the stepper motor and not operator error.
Mechanic says it is the clutch plates sticking, due to just suction or so he thinks, and this is why the revs hang only on low speed town riding downshifts. On the highway or on upshifts the greater forces easily overcome the sticking.
Unfortunately he said he cannot do much about it at the moment but will contact Triumph to see what they have to say about it. He isnt going to do any exploratory surgery under warranty to see just yet. In the meantime it doesn't hurt anything but is a real nuisance having to wait to gear down.
Hopefully in time it improves, but there's still 1 year of warranty left.
Sounds very similar to a problem I had, which ended up being a frayed and finally snapped throttle cable.
I can imagine how this could stick at the lower revs but not at higher, tension in the cable etc, sticking point within the cable sleeve.
If you blip the throttle with the clutch held in, does it die below the 2500 mark quickly or still hover there as it does now ?
Anyway the cable check is easy, a well lubed non sticking one is feather light to use, you could move the throttle with your fingertips. A poor/rusty/frayed one takes a bit of wrist in the throttle action.
TJ, which dealer are you going to? I tested this on my 06 and found that it does do it a bit, and it's just the ECU and the clutch doing their thing. Beware the dealer isn't trying to sell you something like a gearbox and clutch repair.
Once you learn the blip and down change method, you'll never notice this again.
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