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Help Suzuki GSXR250 revving issues

Discussion in 'Suzuki 250cc In-line 4's' started by Simon, Sep 9, 2018.

  1. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Any ideas greatly appreciated on the following:

    Bike is currently totally stripped. Intermittent ignition/fueling fault. Symtoms are runs fine, and then doesn't!!

    (Running all ok)

    And now the fun bit, with the problem


    Its almost like it starves of fuel, and then somehow rights itself. I'm plucking at straws here but its almost like it starts loosing cylinder vacuum (hence the carb balancer) in the second clip, but then somehow starts to clear itself.

    Thanks for any and all help/ideas,

    Heading back to the unit to work on it now!!

    Cheers from blighty,

    Si
     
    Last edited: Sep 9, 2018
  2. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    ..Even the video link is a problem..try again..



    Thanks guys
     
  3. Bob Sykes

    Bob Sykes Active Member

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  4. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Hi Bob and thanks for the reply.. it's exactly the same with the tank on or when it's run off a dummy tank..
    Cheers, Simon
     
  5. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Could it be an air leak on your carb boots ?
     
  6. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Just removing them now lol ... tested ok with a can of wd40 sprayed all over and no change in engine rpm.. thinking unlikely as it's happening across all four cylinders at the same time.. but back to basics..air, fuel spark cheers pal.. keep suggestions coming.. there needed!!!!
     
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    It sounds like it is not running on 4 cylinders. Plugs, leads etc all good?
     
  8. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    All good on the cylinder count, compression 200,200,205,200, exhaust header temperatures (when it's running right) 240degrees on all (taken with an infra red temp meter).. when it misses its seems to do it on all four.. at the same time.. could it be the cdi.. crankshaft pulse sensor is 330 ohms which is in spec..
     
  9. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    .. new plugs cr9e and genuine new Suzuki leads and caps.. don't ask what they cost lol
     
  10. Wozza

    Wozza Active Member

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    Hmmmm sounds like its running out of fuel across all carbs...Id run it till it runs rough then stop it and crack the bowl drain screws,see how much fuel comes out...it will prob be something that is common to all four cylinders..fuel line,t-union, vent tubes, float heights,coil voltage ect ect...also sound like a bit of rattle..cam chain clutch basket?
     
  11. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Cheers for the reply wozza.. that's exactly what it sounds like ie running out of fuel across all four cylinders at the same time.. had a busy day today with not much progress. So far the followings been done:
    Checked battery ok
    Checked coil resistance - primary and secondary, ok
    Performed second test on coils using a spark jump tester, spark will jump 10 plus mm so I'm guessing the coils are good
    Checked out the voltage going too the coils 12.5v and 12.54v. All good.
    Then checked negative terminal on each coil, engine running, 12.5v and 7.2v on the other coil. Replaced that coil and the wiring to it and from it. Now voltage the same too and from both coils, I thought I'd fixed it.. but no the problems still there!!
    Checked signal generator ok
    Removed carbs. Opened up and they are spotlessly clean. Examined inlet rubbers. One was still serviceable but had signs of cracking starting to appear - changed it for a good one. Replaced the plugs for new again on the off chance that the other plugs( also new) were faulty. Checked again that spark is arriving at each cylinder by grounding to the frame, all good. Built it back up. Hey presto - all is good. Took it round the block and same symptoms returned after less than 5km. Bit stumped but will start by cracking open the float bowl drain plugs when the problems happening and see what quantity of fuel is in each bowl to see if you've got a point wozza - never seen it happen before but maybe floats sticking shut?? They looked all good earlier but that will tell conclusively if it's through lack of fuel.. thanks for all the comments - keep them coming, I'm off for a tinney or two!!!
     
  12. ShaneP

    ShaneP Well-Known Member Premium Member Contributing Member

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    The reg/rec or igniter might be failing when it gets hot. Check voltage or unplug the reg/rec when it starts failing. Test spark when failing. All four cylinders failing at once seems bizarre for fuel, I'd be looking electrical.
     
  13. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Done a bit more Shane.. and yes I'm looking at the whole lot.. unplugged the three yellow wires running off the generator/ flywheel earlier and ran it off the battery only.. it seemed to work fine.. so took off the LHS engine /stator cover.. stator looked fine and the three wires were giving a/c current output of between 20-70v each.. rectified the battery infeed was consistent 13.5-14.8v dependent on rpm and load(headlights) ..ive had a mossfet reg/rectifier fitted for a year or so and this seems fine. What didn't seem fine was the magnets on the flywheel which initially looked intact and were obviously supplying enough charge to the battery.. but on closer inspection yielded shocking results.. Will try to post now.. basically three of six were cracked in half.. is this the problem?? Obviously won't put it back together until I have this issue fixed as I'm lucky it hasn't trashed the engine as this part is wet lubed with oil..could the magnets be the actual cause of the issue.. it looks like there for charging only as the cdi signal generator is a pickup on the opposite end of the crankshaft.. thanks to everyone for helping 15365284707391322655825.jpg 1536528510712714982094.jpg 1536528510712714982094.jpg
     
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  14. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Good find on those magnets.
    I'm still thinking running out of fuel. What happens if you mount the aux tank higher (like to shed roof) to give more fuel flow? Can you be absolutely sure there is no blockages in the fuel feed pipes to the needle and seats?
     
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  15. ShaneP

    ShaneP Well-Known Member Premium Member Contributing Member

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    If murdo is right, then you can test by using clear hoses off the drains like you would for float level testing. Run the bike and see what the fuel level does.
     
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  16. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Anyone know of anyone with a Gsxr 250 Gj73a flywheel for sale - part no marked GP9147 9J Kokusan Japan, Suzuki genuine part number 31402-06C00..model specific.. looking at the microfiches the gj72a Gsxr and the across/Bandit 250 flywheels are different.. though in worst case I think they could be lightened and balanced to fit...
     
  17. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Will do Shane.. Cheers boss as think it's likely electrical as well and the flywheel is definitely goosed.. Will double check the fuel level in the float bowls with clear tubing so I can see what it's doing in terms of fuel flow as it starts to misbehave :help:
     
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  18. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    You said you disconnected the alternator and ran off the battery and same thing happened, so makes me think that finding the cracked magnets was just lucky find.
    What happens if you pull the choke on while it is playing up?
     
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  19. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    15365301348771058772849.jpg

    Am I right in thinking fuel pressure??? There's no fuel pump on these there operated by gravity and by a vacuum generated via the fuel tap in conjunction with a vacuum feed off cylinder 2..basically pull the carbs (disassemble the bank), inspect for blockages and thereafter raise the 'dummy' tank higher, then check the bowls for fuel after reassembly if/when the problem re occurs? Cheers matey will check as above (please advise if i'm wrong at what I think you suggest) and come back with the result..im perplexed as I think its electrical at this point as it comes and goes..ball ache lol but its an easy fix when I find out whats bloody wrong!!!!! Love these bikes :):):)
     
  20. Simon

    Simon Well-Known Member Premium Member Contributing Member

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    Lucky find is possible as I cant see how the flywheel can interfere with either cylinder vacuum or fuel flow..hit the choke to richen the mixture and it flat stalls..makes me think not fuel as it should pick up at that point..never been beaten but this one tough boss!! I'm thinking new cdi, new crankshaft sensor..the rests already new..and then probably shell out for a nos loom and thereafter another set of FCR's..then when it still happens just go in a corner and cry, admit defeat and that this one has me stumped!!!! Cheers for helping us out boss, sim
     

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