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Choppy throttle

Discussion in 'Technical and Troubleshooting Torque' started by vanman37, Mar 23, 2007.

  1. Please move this post if in the wrong section. I have used the search function but haven't obviously found this topic or anything resembling it before.

    My concern is regarding how choppy my throttle becomes over undulating or rough surfaces. I initially thought it was a suspension issue (and am still hoping that is the case, because it's easier to fix than retraining my riding style). My current ride is a Daytona 675. I've not experienced this phenomena on any other bike I've owned - but admittedly this is my first "pure" sports bike.

    Essentially, when cruising at CONSTANT speed (ie: neutral throttle position) over a rough or undulating surface, I find that the weight transfer causes my throttle hand to instantly shut the throttle - not all the way, but just enough to cause deceleration. As soon as the bike is over the bump and the chassis has settled, my hand rocks back to the previous position and off I go again. Of course, this all happens in a tenth of a second - very quick and noticeable to me.

    The effect is a stop-start-stop start kind of action - frustrating to say the least.

    I have several recommended suspension fixes to try, from stiff to soft and will apply each over the next few weeks and see if any setting is better, and work from there.

    In the meantime, I wondered if other riders (probably the head down, bum up riders) have experiences similar problems and have successfully located a solution or workaround. Thus far, all I've been able to use as a workaround is to brace my throttle hand with one finger against the brake lever to prevent the forward motion of the throttle which causes the off-on action.

    The only other workaround I've found is to adopt a racing crouch so my wrist and forearm is parallel with the ground - not really practical for commuting (and looks damn silly at 60kph), or to sit with my balls wedged against the tank, upright as possible and placing near to no weight on my wrists, but even then the problem can occur.

    Does this make sense? Hope someone has experience they can share.

  2. This is a general problem with many fuel injected bikes, and was annoying on the Hornet9 I had. Carbed bikes tend to be smoother on the transition from closed to open throttle but less aggressive and precise with their fuel delivery.

    I think it's something to do with the very thin end of the injection map - basically what happens between no throttle and bugger-all, or bugger-all and bugger-all plus one. Also, how quickly the engine is tuned to let the revs drop off when the throttle is released.

    Also, emissions regulations and their effect on bike setup can play a part in creating a choppy throttle response. On some bikes, a new exhaust system and remapped ECU (via power commander etc) can deliver a smoother ride, on others, simply removing some of the emissions control gear from the bike can have a similar effect.

    On the Hornet, I was moving toward a nice smooth transition by adjustment of the throttle position sensor and replacing the intake air temperature sensor with a simple resistor (thanks Pete the Pom) which made a noticeable difference (until I smashed the shit out of it a day later). Pete had success using similar mods and removing the pair valve from several VFR800s.

    Hondas are particularly known for their snatchy injection (although the 06 onwards blade is excellent), whereas Suzuki has a particularly good reputation for designing injection systems that are as smooth as a well-set-up carburettor bank.

    A snatchy injection system is not only annoying, it causes pilions to bang helmets with you in traffic and contributes to rooting your chain and sprockets at a quicker rate.

    I don't know of any fixes for 675s in particular, you might want to check the worldwide forums to see what others are trying, or contact a very knowledgeable triumph mechanic and describe your symptoms, they might have some ideas. If it's a PC3 they recommend, tell 'em to get stuffed, those things are way too expensive.

    The other option is to learn to ride around it - don't coast in gear, pull the clutch in when you're rolling slowly.
  3. I have the same problem on the injected Z750. :( None of the carb'd bikes were as "digital" as this one is.

    I'm having problems with "helmet bash" as Loz mentioned, however riding the rear brake a bit seems to help at low speeds/throttle openings.

    Good luck!
  4. Yup - I have a new can and map loaded designed which opens the intake air valve from idle, rather than from 4,500rpm as is the case with the stock map. There is no noticeable difference to this problem, though I appreciate the low end torque increase in the twisties!!!

    This makes a lot of sense. I am not sure whether there is an equally sensible workaround for this. That's way beyond my level of knowledge, but I appreciate the thought.

    Its hard to not 'coast' in city traffic. Not coasting, rather maintaining a constant speed is where I'm having the problem, and it's only when I hit bumps or undulations. I can't really use the clutch in this situation.

    The problem I experience is not related to speed, but related to trying to maintain a constant speed with a neutral throttle position (ie not decelerating or accelerating) The bumps upset this, causing chop.
  5. I don't carry a pillion. I took the rear pegs off. the wife hates me for it. :grin: I am not certain that riding the rear brake in this situation is feasible, as I would virtually have to ride it all the time on a routine commute, such is the crap road surfaces around the city.
  6. Past bikes have been analogue throttles and you're right, this is digital and by nature is either on or off. That's great when riding spiritedly, and though I'm yet to do it, I imagine would be brilliant on the track. But tracks are smoother generaly, and I imagine this problem would all but disappear given a smooth road surface like a track.

    It's very confidence sapping I'm finding. Nothing worse that setting up for a corner, then rolling gently on the throttle through the corner, only to hit a bump mid-corner and chop the throttle. Less of a problem the more I accelerate - because I'm applying downward pressure to the throttle which more than compensates for any small rocking off motions transmitted to my hand via the chassis.

    So I'm wondering, is there a modification you can make to the throttle itself, to make it stiffer or make the recoil spring more gentle or somehow change things so that, when I want the throttle to wind off, it does, but when I don't want it to, it's much less likely to do so as a result of an incidental weight transfer?
  7. It really sounds like a riding style issue to me - holding on too tight to the 'bars, or keeping your arms straight and locked. You need to keep your elbows bent and remove any weight from your wrists to stop this from happening (and to allow your front suspension to work as it should). The way you're riding at the moment you're limiting how effective your bike's suspension is.

    I realise it's difficult to really keep your arms bent on a sportsbike when you're just putting around town, but it really is the solution to your problem. :) Perhaps you need a bike that isn't so 'head-down, bum-up'?
  8. Yep - I'm sure riding style plays a role here without a doubt. However, if it were ALL riding style, then I would have had the same probem on the other 2 x 675's I've ridden in the past month - but I didn't. So given that my riding style is the same on all 3 bikes (I presume) then it makes sense in my head that there's something about my bike which is different to the other ones.

    I'll have to go back to the dealer and 'test ride' their 675 again and then check out the suspension settings I think. Then I'll get them to ride my bike and theirs and comment on what might be causing the difference.

    And I'll be sure to visit them with relaxed wrists and tired abdominals :roll: