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Bike goes dull at 4000 to 6000 RPM whilst riding

Discussion in 'Technical and Troubleshooting Torque' started by goff, Nov 27, 2012.

  1. Hi all
    Suzuki gsx 250 1980
    It's a bit hard to explain but I will give it a try while the bike is at idle & stationary I can increase the rev range and there seems to be nothing wrong with the bike. But when I go for a ride the bike hesitates in every gear between 4000 rpm to 6000 rpm then past 6000 rpm she just take off a bit like power band, also at speed say 80klm she does'nt like a high gear as it drops the rpm, but go down a gear the bike seems happier to be reving above 6000rpm and has more response.
    Changed the ignition control unit
    Changed the rectifier
    Checked the wiring for continuity
    Checked coils with multi meter they read fine according to manual
    Checked contact breakers and applyed strobe light all good and on timming mark
    New spark plugs with right gap
    Diafram in carby all good
    Clean fuel
    If anyone has any answers or ideas I would be glad to read them
    Cheers Goff

  2. Has it always done it (ie since you bought it), or has it only started doing it recently?
  3. yer
    what jd said
  4. It has always done it but the rev range felt less now the rev range seems greater so it taking longer for power to arrive
  5. My first thought was that the needle height of the carb was set wrong, but not sure how this could get worse over time unless something's really badly worn.

    Other thing to check would be for blockages in the fuel tank breathers and maybe also the fuel filter.
  6. Sounds like a 4 stroke wanting to be a 2 stroke.
    Bout where you stating is where torque turns into horsepower, give or take a grand either side.
    Does that shazuki run the pistons together ??? as in the both go up and down together and because so have a bloody great 5kg counterbalancer hanging off the crank like the the GS500's ???
  7. I checked fuel filter about 4 weeks ago looked clean but will check for blockage in the breathers, also tempted to buy a carby kit?
  8. Always goes slugish around th 4000 rpm and power comes back at 6 to 6.5rpm it does have a counter balance shaft.
  9. What type of exhaust system does it have? The original exhaust had a crossover pipe under the engine that would rust out, and sometimes people would cut them off & blank off the hole in each pipe. This sometimes would make them run a bit funny. I had a 1981 model which I fitted a two into one transarc exhaust, and like yours would take off above 6000rpm but had a flat spot for 500rpm somewhere between 5-6000rpm, and no amount of jetting would resolve it. I put it down to cam profile and the pipe & just rode around it. But yours being a 2000rpm wide flat spot is more of a problem.
    Have you completely dismantled the carbs & given them a good clean?
  10. I took the top of carby off and checked diafram, also had a look at float chamber looked quite clean but i think i should get a kit for it. the exhaust is not original and the R/H silencer is missing the inner tube? I am suspect on the exhaust.
  11. Kinda what I was getting at. If it's down on power, and counterbalancer, and flat spot from leaky exhaust...what would have been slightly noticeable is now rather prominent.
    All motors have that little flat spot somewhere in the rev range.
  12. Carb kits don't necessarily fix running problems except by pure luck. It's the full dismantling, cleaning & attention to detail that's important.

    What about the crossover/link pipe, joining LH & RH pipes together. Is it still there? The RH muffler sounds dodgy, might be time for a new exhaust.
  13. The crossover link pipe has been removed so maybe instead of a carby rebuild, try a new exhaust i will start my search for one tommorow, take it out for a rev fest.

    Thanks for all the replies
  14. check and clean the air filter if it hasnt been done recently as well.
  15. you never answered the first qu.
    from jd.
    and when did the symtom start and
    what happened around same time
    etc etc ...
  16. Cleaned out air box and repaced air filter,and applied new oil on filter, the symptoms were always there with but the but not as great rev range of between 4500 rpm to 5000 rpm. Then one sunny sunday about 4 weeks ago went for a ride to Yea with a mate and thats when it all went a bit wrong. Since then have replaced all those bits mentioned in first thread,and last night removed the other inner pipe out of LH exhaust, so now both exhausts are the same and went for a ride and presto the bike is riding quite good, seems to be breathing alot more freely and the rev range is about 4700 rpm to 5000 rpm so theres a 300 rpm hesitation spot. Have not been able to find an original exhaust, had a chat to a parts supplier whom has 2 silencers for sale but I'm not sure if it will suit my bike ? I.E air flow or do I fit them and then get the bike tuned.
  17. My thoughts too. I'm betting the emulsion tube is flogged out and the needle is worn. Pretty common occurance on any 80s bike.
  18. An easy fiddle would be to run a tank with a fuel system cleaner added. Wynns has a decent one that I used a couple of months back (also in a carbed bike).

    Even if it doesn't bullseye the problem, there's a fair chance on an old bike that it'll clear some built-up crap out of the needles. Might as well drain the float bowls as well, if you haven't yet, for the two minutes it'll take.

    You mention checking the coils, but have you checked the leads? Again, something that might just help in general. For what it'll cost to have top-shelf ones made up, there's little to lose.

    You might also try different fuels if you normally just use just the one, and I'd avoid 91 of any sort as well as the independent brands, just to rule out the fair chance of it being being crap.

    The botton line though, is that bike always need a good handful of revs to get moving much, so any thing that makes a hole in the middle of the range is really going to be felt.
  19. Gday
    Ibast, Where is the emulsion pipe located?
    As a metal worker I am going to play with the exhaust as I cannot find an original one, as it has made a big difference with what i have done so far.
    Wayned I have brought some fuel system cleaner will try it tommorow, cheecked coil leads pull and turn all seem good, check on multi meter all good, And always buy good fuel.
    I keep you all posted but it is getting better.
  20. Teh emulsion tube is what americans call the needle jet. It's the brass jet the carbie needle slides up and down in. It is a precision diameter and needs to be in good condition for correct carberaton in the mid range.

    Also, if the bike has always been that way, then adjusting the height of the needle may solve the problem, but you need to check the needle and jet are good first.