User Tag List

Dislikes Dislikes:  0
Results 1 to 13 of 13

Thread: GN250 strange behavior from 6k rpm and up

  1. #1
    New Member
    Join Date
    Sep 2018
    Location
    Denmark
    Motorbike
    SV650s
    Liked
    0 times
    Posts
    3
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    GN250 strange behavior from 6k rpm and up

    Hi
    I have a GN250 1994 model that behaves oddly. It has the expected pull from low rpm and power gets feelable lower from 6k rpm and up.
    I have cleaned the carbie, cleaned airfilter, adjusted valves cleaned and changed fuel, new CDI.
    Compression is around 185 PSI and should be fine ?

    Any ideas ? as i'm running out ?

    COuld it be a weak sparkplug ? ignition coil or other ?

  2. #2
    Member Scrap's Avatar
    Join Date
    Jun 2009
    Location
    Perth, Western Australia, Australia
    Motorbike
    Yamaha Road Star 1600
    Liked
    18 times
    Posts
    443
    Post Thanks / Like
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    GN250?

    Known to have problems with rectifiers.
    Life seems more precious when there's less of it to waste.

  3. #3
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    8,198
    Post Thanks / Like
    Mentioned
    35 Post(s)
    Tagged
    0 Thread(s)

    .. it's the battery...
    " Imagination is the seed of life..."

  4. #4
    Member Loud's Avatar
    Join Date
    Dec 2009
    Location
    South. Just.
    Motorbike
    Aprilia RS250, GSXR750 Slabbie
    Liked
    906 times
    Posts
    4,885
    Post Thanks / Like
    Mentioned
    96 Post(s)
    Tagged
    0 Thread(s)
    Why did you change the CDI?
    Click Link for My Bikes:

    Aprilia RS250
    1985 GSXR750 "Slabbie"

  5. #5
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    8,198
    Post Thanks / Like
    Mentioned
    35 Post(s)
    Tagged
    0 Thread(s)

    is it getting full throttle when you twist the grip..? will it rev out in lower gears..?
    Have you replaced gaskets and seal in the carb? Set float level--checked air breather vents not blocked?
    if you used carb clean with the diaphram in they will be damaged slightly.. Check alignment of cap- spring -slide diaphragm for creases splits etc. Is needle free to lift fully up? Use ya finger in the back of the carb...
    Checked for vac leaks.. ( check the fuel tap? Ride with tap on 'prime.'. note differences.)I guess it is a vac type tap
    Full throttle test is it..? You need ..max air flow--max fuel flow-around about 12.5v to 14.5v ( at the battery/power feed) -max timing advance.(cdi takes car of that) or should
    .good spark..91 ulp should be fine..8.5:1 comp?
    It's a tiny gutless engine..so you need everything to be perfect before they run -on song-
    Check battery frame earth return circuits..add wiring as reqd. mi2c is carby..
    " Imagination is the seed of life..."

  6. #6
    Staff BlackFZR's Avatar
    Join Date
    May 2006
    Location
    PSB Headquarters
    Motorbike
    2 x R1's
    Liked
    646 times
    Posts
    7,597
    Post Thanks / Like
    Mentioned
    131 Post(s)
    Tagged
    0 Thread(s)

    I assume by power, you mean that it doesn't feel like it is accelerating as quickly as it used to once you get higher in the rpm? Does it occur in every gear? or just the higher gears? Is the clutch slipping?
    Sponsored by:

    Billetta Imports, Motorcycle Panel & Paint, Pirelli, YAMALUBE

  7. #7
    New Member
    Join Date
    Sep 2018
    Location
    Denmark
    Motorbike
    SV650s
    Liked
    0 times
    Posts
    3
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I have fully rebuild the carburetor, and fully cleaned as well. No carb cleaner on the diaphragm, and have checked them for holes.
    I bought a complete rebuild kit, all new springs and jets. Compression is fine, and I have done a leak test where the carbie goes to the engine.
    Just today I notised that it pops some in the exhaust on deceleration. not much but some. I was wondering if it could be the camchain that has slipped a notch ?
    I replaced the CDI because it feels like ignition runs retarded.... or at least fires too late. or it could be flow into cylinder?
    The throttle opens fully, and the same behavior in all gears. it seems to loose all willingness above 6k.

    - - - Updated - - -

    Yeah I know that "power" is somewhat an overstatement but less than it should have. And no clutch is not slipping.
    And engine have only run around 12K kilometer. and 185 psi compression says that it's not broken

    - - - Updated - - -

    Quote Originally Posted by GsxInShed View Post
    .. it's the battery...
    Battery is brand new GEL type 12,3 Volts (14,6 running)

    - - - Updated - - -

    Quote Originally Posted by Scrap View Post
    GN250?

    Known to have problems with rectifiers.
    Can rectifier do any of the above ? besides cooking or undercharging the battery ?

  8. #8
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    8,198
    Post Thanks / Like
    Mentioned
    35 Post(s)
    Tagged
    0 Thread(s)

    mmmm... blocked exhaust? Valve timing checked?

    Carb jets in the right places..? Might be nothing ..yet there are 2 that look alike yet make a huge difference in running. ( not too sure tho'....above 6000 rpm should be all jet needle and needle jet..Main.)
    " Imagination is the seed of life..."

  9. #9
    Member Loud's Avatar
    Join Date
    Dec 2009
    Location
    South. Just.
    Motorbike
    Aprilia RS250, GSXR750 Slabbie
    Liked
    906 times
    Posts
    4,885
    Post Thanks / Like
    Mentioned
    96 Post(s)
    Tagged
    0 Thread(s)
    Sounds frustrating.

    If it's all factory settings and you're 100% that the carb isn't blocked and has fresh fuel, then I'd be concentrating on ignition.

    Pull the plug, earth it to the bike and hit the starter. Is it a strong spark? A weak spark would be enough to get the bike running but it'd break down at higher RPM.

    If that's fine though I'd consider calling out someone like Derek Ball to check it out. A fresh set of eyes and decades of experience is worth the cash and saves you from going postal.
    Click Link for My Bikes:

    Aprilia RS250
    1985 GSXR750 "Slabbie"

  10. #10
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    8,198
    Post Thanks / Like
    Mentioned
    35 Post(s)
    Tagged
    0 Thread(s)

    He might be in Denmark ( not the one near Esperence )
    " Imagination is the seed of life..."

  11. #11
    New Member
    Join Date
    Sep 2018
    Location
    Denmark
    Motorbike
    SV650s
    Liked
    0 times
    Posts
    3
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I am located in Denmark This forum just seems to have a huge technical knowledge base. So I thought i'd try it out.
    Will have a look at the ignition, and the valve and cam timing.
    Likes Para045 liked this post

  12. #12
    Member Water pig's Avatar
    Join Date
    Jan 2016
    Location
    Yanchep
    Motorbike
    Cbr 500r, crf 250r, Daytona 675
    Liked
    0 times
    Posts
    517
    Post Thanks / Like
    Mentioned
    3 Post(s)
    Tagged
    0 Thread(s)
    I'm guessing it's cam timing as well, where abouts in Dk are you living? My wife's a Dane and my oldest boy is currently living there and going to university

  13. #13
    Member GsxInShed's Avatar
    Join Date
    Jun 2010
    Location
    Next to the big hole in the economy
    Motorbike
    (TY-250- RD350LC- Gsx 750 esd) Current -Gsx 250 SSM GSX 1100 EFE
    Liked
    304 times
    Posts
    8,198
    Post Thanks / Like
    Mentioned
    35 Post(s)
    Tagged
    0 Thread(s)

    I see by your posts on KiwiBiker the problem has resolved itself..

    After "fiddling with the cables"..? you mean hoses eh? kinked breather hose..?

    Nice to see the weather is warm 0-5 deg C mmm luvly...

    Any hoo .. all the best .. elverdane ;-) Enjoy the ride...

    The whole story was at wot.. it would lose power then downchange made it worse.. pull over and rest the bike for 5 mins get on ride off and all is good for 15min then goes to shit again..

    Waddayaknow....?
    " Imagination is the seed of life..."

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •