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GN250 won't start cold

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by RetroRacer67, Jul 9, 2014.

  1. Hi there,
    My current project is based on an '85 Suzuki GN250
    Most of the changes have been superficial/aesthetic, but it is giving me some headaches now at the sharp end.
    When purchased it had apparently had the piston, rings & head replaced/rebuilt, & had only done 30k's since. I did start & ride it, but for some reason the guy had used 2 stroke in it so obviously it didn't go too well.
    During the rebuild the tank was soaked & cleaned (yes, it was somewhat gummed up) as was the carb. I put an inline filter on it, just to make sure no rubbish would come through
    Carb was stripped, soaked & cleaned. Jets seem standard, float adjusted as per spec. Pod filter fitted. I guess I'm saying at this stage I don't believe the issei is fuel related?
    It refuses to start cold (with/without choke or throttle) unless "Start Ya Bastard" is used. It will then start & run rough, until it warms up. Idle mixture done (@1 ¾ turns out, so close enough), but seems to me to be generating a lot of heat through he engine/exhaust?
    Idle does seem to vary a bit.
    Apparently the timing isn't adjustable?
    Any ideas would be greatly appreciated, because I have no hair that I can tear out };(

  2. Not starting cold would indicate lean (if everything else is right). Some bike manufacturers set their bikes up lean to meet emission targets in some markets. Suzuki was on of these. Give it another 1/2 turn out on the idle mixture screw. Do you know what the factory setting was for sure? 2 is very common but not always the case.

    Stupid question, but you do understand the difference between a idle mixture screw and the idle speed screw? Just checking as some that come here don't.

    Also, what is your idle speed once it is warmed up?

    Replace vacuum line to the tap. It's cheap, so don't frig with it even if it looks good.
  3. Hi, & thanks for your reply.

    Yes I do know the difference, & no that's not a silly question. I do have the factory specs but nevertheless will try to richen it up. The too lean issue may also explain the seemingly excessive heat, too?

    Have no clue what idle speed is, as I removed the tachometer! However, I have it set as low as I can without it stalling on idle.

    Will replace the line, good thinking.

    Thanks again, will keep you posted.
  4. Yes, lean makes it run hotter.

    Set the idle speed 10% above when you can get away with. This allows for changes in ambient conditions, fuel, etc. It's also a bit nicer on the bike.
  5. Ok,
    Fuel line replaced, along with inline fuel filter.

    Still didn't want to start cold, but persisted the warmed it up. Once idling ok, fiddled with mixture screw some more. Is definitely better on idle now, so a combination of the above has certainly improved things. But still no cold start }:(

    Just thinking, although it looked ok when I had the carb apart, would the diaphragm cause this if it was leaking?
  6. Ok,
    Gone as far as I can with the fuel system, so now looking more seriously at the electrickery.
    Won't start cold/runs hot/backfires = timing too far advanced, right?
    As I still can not believe that an '85 model would have electronic ignition I removed the magneto cover to see for myself if there was anything at all adjustable but no, nothing doing. All seemed to be as it should.
    So, the cdi unit. Borrowed an ohm meter & sure enough there are several readings out of spec.
    Have ordered a replacement via eBay, so now we wait...
    • Informative Informative x 1
  7. Check the rubber boot between carb and engine for cracks, if it leaks and lets air in = too lean / hard start.
    If you cant see any try squirting WD40 or similar around it while its running and if idle increases theres your problem.

    My old Ducati is a '78 AND it has electronic ignition :) so dont be so surprised
    • Agree Agree x 1
  8. Thanks for that-have checked & sprayed. Right now the cdi seems to be the culprit. Have a replacement ordered, hopefully that will be the end of it.
  9. Back again...
    CDI unit replaced, issue improved but not resolved. Rechecked mixture, again slight improvement.
    Have solved the ridiculously hot running issue though, so at least we're no longer too advanced.
    Head needs a re-tension anyway & have no tension wrench, so have booked it into the mechanics for a tension & valve clearance set. My fingers are crossed this will be the end of it
    All I wanna do is ride!!!
    • Like Like x 1
  10. Thread title made me look twice.
    A 3 degree morning in Adelaide and my GN250 wouldn't start. Not quite true. The choke was stuck. It started eventually and by the time I got to work the choke moved freely again. What would cause the choke to stick on a cold morning?
  11. could just be a bit of moisture and gum in there. It's basically a plunger with an o-ring. Needs to be pulled apart, cleaned and put back together.

    Carb problems always come out in winter.
    • Like Like x 1
  12. And finally...
    Re-installed original airbox (just to eliminate my doubts about the pod filter), replaced the stator unit as well (some cooked posts), finally discovered a blocked pilot jet.
    All now running sweetly, thanks to all for their input.
    • Winner Winner x 1