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GSX250 only running on one cylinder, wits end.

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by tornaido3927, Jul 8, 2013.

  1. Hey everyone,

    I've recently undertaken a project which is an '85 GSX250 (twin cylinder, BS30SS CV type carbs) that I started working on a month or so ago. After lots of work I have finally reached a point where the engine should be running. I can get it firing and idling but only on one cylinder. :(

    I have cleaned out the carbs to the best of my ability (I have no way of reaching the transition ports at the butterfly or the middle of the choke tubes, etc) but I definitely CAN smell fuel coming from the exhaust of the non firing cylinder. There is lots of spark and I have even tried a spare coil (have a spare parts GSX250 as well) to the same end.

    Even though I can smell fuel from that exhaust; after pulling the plug it is dry. I even threw in a brand new plug, ran the bike and pulled it, still looks brand new and shiny as when I put it in. Still sparking like a champion too.

    I have no idea what could be left to check and if I need to take it to a shop so that they can check for flow or air leaks or something then I will, but as a project bike I'd really like to try and nut it out myself, any ideas on where I can start troubleshooting or what the problem may be?
  2. Timing perhaps? Just a guess. Nothing else to offer :)
  3. One diagnostic test to see if it is a fuel related problem is to spray aerostart/startyabarstard/ether into back of carb of the problem cylinder, and if it runs for a few seconds each time you give it a short squirt, then you know it is a fuel supply problem.

    Have you done a compression test?

    Have the camshafts been removed & replaced? Had problem once where cams were set up using no'2 cyl at TDC instead of no'1cyl, and it would only run on one cylinder. DOH. Re-did the cam timing and then it ran like a clock.
  4. If the plug is dry when you pull it then its not getting fuel, or at least not enough fuel. Have ya tried cranking it with that throttle blocked? Can help to get the fuel flowing cause it applies a lot more vacuum to the carby orifices/jets etc. If its just a random bit of crud blocking something or a sticky needle and seat it might get ya going again
  5. Never even thought of timing or cams. I haven't touched any of it as I was told that it was running prior to being garaged for years, but I really should check.

    I have two cans of startyabastard and I never thought of that either! Must be having a brain fart under my frustration :( That'll be good though, I have been most confused as to whether it is a fuel supply problem or not considering the carbs were originally in a bad way but should be fine now. It may well not be getting enough but the exhaust does smell quite fuelly, not that it is conclusive at all. So I will start with the startyabastard tomorrow, following that if it doesn't help I will proceed to check timing and cams and stuff.

    Thanks heaps guys! I'm happy if I at least have something to work towards!
  6. I don't understand why the plug is dry if I can smell fuel in the exhaust though, I'll have a go at blocking it off a bit and see if it helps.
  7. #7 sl100, Jul 8, 2013
    Last edited: Jul 8, 2013
    Check out this thread of mine from a few months back, https://netrider.net.au/threads/carby-bowl-gunk.149428/
    I thought i had the carbs cleaned out but i had to pull em/disassemble/clean again to get it running right:banghead:

    Ohhh, and the fuel smell could be just that. A hint of fuel vapor getting dragged through but no where near enough atomized fuel to allow it to fire
  8. This tells me you haven't stripped & cleaned the carbs properly, start there & I expect you'll find the issue.

    If you have air & spark, you're only missing fuel.
  9. Oh man OK, so it turns out everyone who mentioned fuel was right, I gave her a squirt of startyabastard and it roared to life! It quickly died again but even a few squirts near the outside of that side pod started that cylinder firing like it should. So I suppose it is time for yet another carb yank...

    I really cannot get to the transition ports of middle of the choke tubes, they are just beyond what I am able to do myself. I might have to get the bike shop to really give them a going over, or see if I can pick up an ultrasonic cleaner if that would even help much.

    But at least I know what I need to do, thanks so much for your help guys!! Really appreciate it!
    • Like Like x 1
  10. All you should need to do is take the floats bowls off the bottom, that will give you access to everything you need to clean, ie the jets. Can of carb cleaner from super cheap & you should be good to go, it really is easy.
  11. I've done that three times to both carbs. In fact the carbs now have brand new jets (bigger for open exhaust and intake). The emulsion tube is also clean.
    The transition ports apparently in the BS series carbs need to be clear for them to function properly, hence why I don't think I'll be able to get it clean enough myself. I have even gone to replacing the o rings in the fuel screw which were had it. Also pulled the tops off the carb and made sure the rubber diaphragm was in good nick and the ports for the vacuum section were clear for proper function.