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Loss of power and rev's staying high after a crash

Discussion in 'Technical and Troubleshooting Torque' started by Captain115, Sep 9, 2012.

  1. Hi everyone,

    So I dropped my bike (Honda CBF250 '06) the other weekend, at pretty slow speed, only about 30kmph. Just slid along on the left hand side for a couple of meters and then stopped. I picked her up, checked that everything was still functional (except for the plastic rego holder which had snapped) and off I went.

    Since then I've replaced the clutch lever (aesthetics) and rotated the handlebars back to where they were meant to be (they had been twisted slightly).

    Today is one of the first days that I've ridden it since the crash and since I got a new front tyre on it yesterday, I decided I should properly try and scrub it in. Started riding it around and noticed two things, which may be related:

    1) There now seems to be an engine 'float' when not accelerating. As in, I'll accelerate to about 6500 revs and when I roll of the throttle, the revs stay quite high before dropping off. I'm not actually getting more power during this, it just seems that the revs don't drop back down like they used to. Like coasting down a hill, with the gradient of the hill keeping revs up. Seems similar to an air-leak, that same sort of 'float' before the revs drop back down.

    2) The bike seems to be weaker now at high RPM, like a loss of power. For example, it used to lug if the revs dropped below about 4000, that mechanical noise which lets you know your in the wrong gear. Now, this lugging seems to occur up into the 5k revs, which is where I used to sit comfortably when commuting (below the 7k vibration band).

    I assume that these two events may be related, that I've somehow got an airleak and it's both robbing me of power and making the revs stay high. Like an incorrectly seated carb-to-intake mounting boot or something?

    TL;DR: Had a crash, now the bike seems to have lost power and revs don't drop down. Suggestions why, and how to fix?


  2. Check your airbox to start with mate. Could have copped some oil in there which could account for some of the symptoms.
    Good first place to start anyway.

    You seem to be thinking on the right track. The rpm stuff could also be a vacuum leak yes, id check around the carby intake and base.
    Rough running/struggling at lower rpm is a big symptom of it.

    Anything beyond that is beyond my technical skills :p.

    P.S. may also have stirred up crud in the tank which worked its way into the carby. Worth keeping in mind if the above fixes the main issues but shes still a bit rough!
  3. Depends on how I read the symptoms you describe. The over revving could be the clutch slipping slightly, hence revs increasing when going up hill but no corresponding increase in power delivered. Check clutch cable adjustment, maybe you've kinked the clutch cable...

    Or your throttle isn't snapping back to idle. Check accelerator cable, gummed up throttle action.

    When the engine revs go up and down does it correspond with speed going up and down or are they somewhat unrelated (higher revs but same speed)?
  4. The air intakes for the carbs run from little funnels under the seat, so I'm not sure really what to check there? I was definitely going with the 'spray around carb while running' to see if revs increase to check for airleak. Jest not sure how to check for oil in the airbox?

    I don't have an inline filter that I can see, so it is entirely possible that there could be some crap have made it's way into the carbs too.

    I had a look at the clutch cable and spent quite a while adjusting it since I replaced the clutch lever and it seemed fine. Good thinking though, and hadn't even considered that!

    The throttle cable shouldn't be binding since I lubed them just the other day, but I'll have a look. I sort of thought that since the rev's staying high don't equal continued power, then the throttle action probably isn't stuck. To say that more eloquently, if the throttle was stuck slightly open, would the bike still be accelerating a bit?

    Not really, the rev's increase in line with the throttle like normal but when I roll off the throttle, the power disappears (like it should) but the revs stay high as If I'm still accelerating. They don't drop off in line with the throttle action, if that makes sense?

    Thanks for the suggestion,

  5. Those funnels feed into an airbox, and it's this airbox (part 1) that can fill up with oil/fuel (sometimes to the point of soaking the air filter element). Should look something like this:
    Edit: Oh and start by opening the drain tap (part 14), if nothing comes out then it's probably not the problem. If you do get some fluid coming out then worth cracking open the airbox to check inside.
    • Like Like x 1
  6. See, this is why I love Netrider. I didn't even know that getting oil in the airbox was possible! So I opened up the drain tap (Part 14 on the diagram) and lo and behold, out drains some oil.


    I had a look inside the airbox and you could see where the oil was and then the start of the drainage tube that it must've gone down. So what now? Do I wash the air filter?

    Thanks for the help,

  7. Looks like your bike is using a pleated paper (or possibly cotton) filter in which case just check to see if looks like any of the liquid you drained from the airbox has soaked into it.

    If it has then best to buy a new filter (OEM paper filters aren't designed to be cleaned).
    • Like Like x 1
  8. Had a look at the filter and it doesn't seem as if the oil got onto the paper. No discolouration, doesn't feel or smell oily, so should be ok right?

    I'm glad you found that, as I said I didn't even know that was possible. But would this have resulted in the problems as was having? I mean, if the oil didn't touch the filter (and it seems like it hasn't) would it still effect the bike like I have described?

    I'm not trying sound like a smartarse here, I am truthfully wondering how this all interconnects.


  9. Does sound like it's okay. The main reason for checking is that I do remember a similar thread many years back where someone had dropped their bike and was having trouble getting it to run properly. When they checked their airbox it was nearly full of liquid, and the air filter was soaked which restricts airflow. Needless to say draining and replacing the filter fixed the problem

    The problem lies in the fact that because of EPA regs the crankcase is vented into the airbox rather than to the atmosphere. So when a bike is tipped at weird angles oil can flow out of then engine and through the breathers. On an unrelated note a lot of diesel trucks and older 4wds were exempt from this, which is why the f*&kers leave that trail of oil up the middle of the road.

    Oh and one other thing worth checking is the spark plug. It may have become fouled when the bike was down and that could certainly cause the problems you're describing.
    • Like Like x 2
  10. Sounds like we are on the right path :).

    jd has it covered by the looks of things.
  11. Thanks so much for all the help everyone, in particular you jd!

    I'll have a ride over the next couple of days and report back to see if the problem has been fixed.