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What is going on!?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by jackbaz, Oct 9, 2013.

  1. Hey guys, this is my first post ever and I'm having troubles with my Hyosung GT250R.

    I'll try to explain it as best I can..

    Basically at random points whilst riding the engine cuts out, revs drop then comes back and the revs go to 5-6k rpm
    Then cuts out again and then repeats this until it eventually dies and I have to restart it.

    Now it doesn't always do this, just at select moments. I have absolutely no idea why it's doing this.
    My fellow rider buddies suggest it could be dirty fuel, a dirty carburettor, new piston needed, new carburettor needed etc..
    But these are 'educated' guesses at best.
    I don't really have the funds to take it to the mechanics at the moment so I'm wondering if anyone is able to help me out here at all?
    If it's something simple like replacing the carburettor than I can undertake this task, but I just need some clue as to what the issue could be.

    I'm a daily commute guy and it's killing me not having my bike! Not only because it's my main vehicle but because riding is super fun ;)

    Please someone help!! Any tips or ideas will be very appreciated

    Thanks guys :)
  2. #2 cjvfr, Oct 9, 2013
    Last edited: Oct 9, 2013
    Pull spark plugs out and check the colour of the gap. It can tell you a lot about the mixture.

    • Informative Informative x 1
  3. I'd suggest to pulling out spark plugs as well then check the gap if they're getting wider or they have black dust covering the gap. Is your GT250R feed by EFI or carbie ?
    And what kind of petrol you usually fill ?
  4. Spark plugs? Give me a break.
    You might want to look for an intake air leak.
  5. doesnt hurt to pull out air intake to check as well since its more likely to be ignition problem - air -fuel - spark .
  6. I think the answer lies in your first sentence.

  7. I posted on other thread about Hyo bikes always come with problems and eventually fall apart.
    Some people just got lucky but most of Hyo owners are not that so lucky.
  8. what year model?
    the pre 2011(?) EFI models had a cheep ass charging circuit components that generally just didnt work.
  9. I had exactly the same symptoms with my 2008 CBF250. After multiple trips to the mechanic, and a bit of back-and-forth direct to Honda, the solution in the end was to get the pilot jet changed from standard #45 to #50 - I think the #50 is slightly bigger, but I'm only guessing that because it's a bigger number.

    Maybe suggest a similar solution to your mechanic, or get in touch with Hyo and see what they think.

    Hope this helps.
  10. You wont need new pistons and you wont need a new carbie. well not if you act promptly.

    Firstly, check your tank vent. When it dies next time, open the fuel cap. You may notice air rushing in. Even if you don't, it will release any vacuum built up in the tank. If it starts fine, then this is your problem. The vent is likely in the fuel cap.

    After that I would be checking the vacuum line to the fuel tap. Or if it's FI then the fuel pump. I've had to replace this line on a couple of different bikes, even ehn it looked good, to fix similar problems to what you describe.

    As suggested above, it could be spark, but I'd start with the fuel, given the symptoms you've noted.

    Spark it fairly easy to check. Pull the plug and put it back in the lead. Earth it on the side of the engine and push the starter button. You should see a strong blue spark. Lower light conditions help this diagnosis. Check the colour and the gap at this point in time.

    If it is not good, then replace the plugs. Hell, replace them anyway, they are cheap enough. Make sure you don't cross-thread them or over tighten them. Take your time and don't yank on the ratchet.
    • Like Like x 1
  11. I've just remembered one of my friend has similar problem.
    he fills E10 every time and the bike dies.
  12. It's an '05 model so it's carby

    I've put premium in it for the past 4 months (how long I've had it) up until a friend said that it wasn't necessary and that it could be harmful for a little 250

    I'm very noob and assumed that the better the quality of fuel the better it should be for the bike.

    Thanks for your tips guys, I won't have time to take a look until Sunday but I'll keep you guys posted if it works.

    Great community on here! :)

  13. Premium or "high octane" fuel can foul the carbie float and gunk up the bowl.

    Higher octane fuel is primarily to prevent pinging (knocking) and detonation in high strung, high compression engines.

    An EFI engine has sensors to advance spark timing, A/F ratio etc, etc, etc.

    Your little'ol carbied Hyo does not.

    Give it the thinnest (ULP) petrol you can. Not some viscous, high-octane jungle juice.

    This might help.
  14. it can also foul spark plugs
  15. I bet your spark plugs are cover with white dust.
    Give them a look so you can diagnose what is going on.
    Since your hyo is not EFI , it really cant adjust the combustion of high octane fuel but it doesnt mean after you fix it you should go for lower grade fuel.
    Bike with carbie feed need the right octane fuel.
    User manual usually suggest the type of fuel that suits the bike best.

    Anyway, after pull out the spark plugs and still cant find something wrong with them then you should give a close look at your carbie.
    Just give it a nice clean then put them back together should be fine.
    The problem happens just at selected moment isnt it ? means your Hyo roughly still ok in some condition but need to check out .

    And last of the last ... if you have any chance just change your bike to be more reliable brand/make. Hyo is too fragile . It takes only a small thing that Hyo doesnt like, then comes trouble.
  16. Ok so I replaced the spark plugs, they looked oil fouled but even then they weren't badly fouled. Replaced them anyway as it was cheap and a good learning experience.

    It's still having the same issues only less frequently, when I have time this week I will clean the carby
    Will also look at replacing the fuel line, may get the mechanic to do that as it seems over my head

    Thanks guys
  17. groundhog_day.
    • Funny Funny x 1
  18. Vapor lock.

    If it's an '05 the tank should've been drilled.

    If not that (although $1000 says it is vapor lock) second bet is a cracked intake joint (between carb and cylinder head) or a leak in your vacuum line.

    Go ahead and google "hyosung tank vent". Somebody has probably got a fix for you out there on the internet.
  19. Just bought a 2009 Hyosung 250 GT, my first bike, a bargain at $1500 with 3000k, so I thought. To date it has shorted its starter motor and welded the starter solenoid, cost me a fuel pump, all because of poor design of the fuel tank breather. So the previous post on the fuel tank venting was spot on. The symptoms of the bike faults of the poor venting are;
    Engine stalls after a few minutes running then is hard or won't restart. When engine under load or sucking heaps of fuel bike looses power, misses or dies. Plays up more frequently on a full tank. I found all this was due to either a vacuum or pressure build up in the tank cause by poor tank ventilation.
    To check if you have a venting problem run your bike as normal, if it stalls, open the filler cap and listen, if a lot of air rushes in. That is your issue.
    Also when you fill up after riding and the tank expels a lot of air you are going to get a problem.
    So before you spend heaps of money sorting a problem that shouldn't exist search the web on Hyosung fuel tank venting. A kind gentleman posted a fix which applies to the 650 Hyosung which works for the 250 as well, it takes only 20 minutes to complete. So ask your repairer to make the change.
    I hope this helps someone in the future.
  20. Because of the reputation of Hyo electrics I would have looked at the engine cut out switch,