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Blip the throttle and revs drop

Discussion in 'Technical and Troubleshooting Torque' started by colourclassic, Aug 30, 2010.

  1. G'day, have an 89 Honda Spada. Was running well until a few weeks ago.

    When accelerating from a stop, the engine seems very hesitant to build revs, like it's bogging up until about 4000rpm. If I blip the throttle from idle, the revs drop to about 800rpm and it nearly stalls. One thing I noticed is, this only happens after the bike has been idling for over 30 seconds i.e. waiting at lights. If I keep blipping the throttle every 10-20 seconds the engine behaves normally.

    Any ideas? Was thinking the pilot circuit/jet may be clogged, but then this problem only occurs after the bike has been idling for a while. Maybe needs new plugs?

    Cheers in advance
  2. Does seem like a carbie problem, though I would say a very small amount of dirt (or gum) under a needle seat.

    Run a tank of e10 through it and let us know what happens.
  3. ibast is probably right. When you're blipping the throttle you're letting in lots of air. If the fuel isn't ale to flow freely enough then you're going to see a drop in RPM due to there being too much air and not enough fuel.
  4. Just tried that, didn't help.
  5. Is your idle set right?

    If so then you might be up for some carbie work. bottom end clean, float height set and a syn.
  6. Yea idle is set right. Ughh, was hoping I wouldn't have to pull the carbies again, it's a PITA, but i'll give em another look, otherwise off to the mechanics (or eBay).

  7. You've been fiddling?

    Are the idle jets set right? Did you do a syn?
  8. Carbies were synced last time I pulled them off, but not since the problem occured. As for idle jets, I've just let the engine warm up and adjusted the mixture screw until the engine sounds 'about right'...
  9. Could also be an air supply problem resulting in flooding the cyl with fuel
  10. Yup, I would also look for flooding. The symptoms you describe fit perfectly. Have you checked if your air filter is clogged?
  11. Nope, but i'll check.
  12. I would think it might be all a bit dirty in there. Like the idle screw, jets, needle and seat.
    A can of Motec carby clean. A very very fine steel wool 00 steel wool if you can find it. 6 beers and about two hours and all good again.
    If adjusting your idle screw does not do anything, then all of a sudden it revs high for a while then falls down to a stall or almost, Then yep. get em off and clean em up. Dont do them on the bike and pass all that crap through to where it will really cost you.