1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Help Acceleration Issue - 1990 ZXR250R

Discussion in 'Kawasaki 250cc In-line 4's' started by Sweeks, Aug 28, 2021.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

    Messages:
    5,102
    Likes Received:
    3,472
    Trophy Points:
    1,148
    Joined:
    Dec 23, 2012
    Gender:
    Male
    Location:
    Thailand
    Home Page:
    My Bike:
    Yamaha FZR400 3TJ1, Honda MC22
    Sounds like a good plan to get to the bottom of this mystery.
     
    • Agree Agree x 1
  2. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

    Messages:
    10,914
    Likes Received:
    6,708
    Trophy Points:
    1,168
    Joined:
    Jun 14, 2012
    Gender:
    Male
    Occupation:
    Between a Rock and a Hard Place
    Location:
    North by NW NSW Oztralia - Tamworth
    My Bike:
    *Kawasaki ZXR250C *Yamaha FZR250R 3LN1 *Yamaha FZR400 *Triumph Bonneville 750 T140V *Triumph Daytona 675 *Triumph Tiger 800XC
  3. kiffsta

    kiffsta Senior Member

    Messages:
    9,066
    Likes Received:
    6,872
    Trophy Points:
    1,168
    Joined:
    Aug 7, 2010
    Gender:
    Male
    Location:
    Brisbane
    I thought the sp carbs were 32mm inlet diameter so how will a set of 30’s fit the inlet manifold ?

    I’d be looking at the slides , at 6000-7000rpm, you are on the main jet with the slides coming up , where are your needles set to ?
     
    • Like Like x 1
  4. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Please explain “where are your needles set to ?”, they are held in the slide by the spring, I haven’t made any changes to them.
    The slides are free and I have checked the diaphragms for leaks.
    These are my first CV’s, any guidance is appreciated.
    I still believe that there’s something going on with the slides, I just don’t know what.
    As you know, you can get to 7k with very little throttle opening, so I’m not sure that I’m getting on the mains fully.
     
  5. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

    Messages:
    5,102
    Likes Received:
    3,472
    Trophy Points:
    1,148
    Joined:
    Dec 23, 2012
    Gender:
    Male
    Location:
    Thailand
    Home Page:
    My Bike:
    Yamaha FZR400 3TJ1, Honda MC22
    The air filter element and air box sealing is all good?
     
  6. kiffsta

    kiffsta Senior Member

    Messages:
    9,066
    Likes Received:
    6,872
    Trophy Points:
    1,168
    Joined:
    Aug 7, 2010
    Gender:
    Male
    Location:
    Brisbane
    Sorry , are the needles shimmed ? Ie has some used washers to raise the needle height ?
     
  7. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

    Messages:
    3,979
    Likes Received:
    2,207
    Trophy Points:
    923
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Occupation:
    Gardener
    Location:
    Tasmania
    Home Page:
    My Bike:
    Spada, VT250F & ZX2R
    Are the Leak Air Jets clear?

    upload_2021-9-9_17-55-39.png
     
  8. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

    Messages:
    4,730
    Likes Received:
    2,870
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    FZR250R 3LN6
    Standard ZXR 30mm carb needles are non-adjustable. No clips. You can only shim/space them to run richer. In the event you need to lean it off, it's either find a set of adjustable ZXR needles (rare) or change the air jets, which are pressed in.

    I have a set of adjustable needles I got off @sharky some time ago.
     
    • Informative Informative x 1
  9. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Yes, clear

    Yes, all good (Litetek seals )
     
    Last edited by a moderator: Oct 20, 2021
  10. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Same part number.
    Carb spigot O.D. Same
     
  11. GeorgeT

    GeorgeT Active Member

    Messages:
    70
    Likes Received:
    31
    Trophy Points:
    88
    Joined:
    Jul 29, 2021
    Gender:
    Male
    Location:
    Glencoe NSW
    My Bike:
    Yamaha 1984 SRX250 + BMW R1150RT
    This sounds like it could be a CDI/TCI issue, i.e., the spark is too short when the rpm reaches a certain point so the spark is too close to the top-dead-center, like trying to run the engine backward almost. I have no idea if this bike used a CDi or TCi but the TCI as far as I am aware enables a longer spark at higher rpm. Older engine systems would just need the spark advanced more to enable smooth running as rpm increases. Maybe worth checking I guess?
     
  12. kiffsta

    kiffsta Senior Member

    Messages:
    9,066
    Likes Received:
    6,872
    Trophy Points:
    1,168
    Joined:
    Aug 7, 2010
    Gender:
    Male
    Location:
    Brisbane
    the symptoms are the same as my old zxr250 where the fuel inlet t piece seals had failed.


    I would be check the carbs for leaks , put the airbox on and spray some ether ( we have stuff called start you bastard) around the fuel inlet t piece , just a small spray and make sure that t piece is sealing correctly , if the revs rise then there is still a leak.


    I have doubts it is the tci, but never say never
     
    • Agree Agree x 1
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

    Messages:
    5,102
    Likes Received:
    3,472
    Trophy Points:
    1,148
    Joined:
    Dec 23, 2012
    Gender:
    Male
    Location:
    Thailand
    Home Page:
    My Bike:
    Yamaha FZR400 3TJ1, Honda MC22
    • Informative Informative x 1
  14. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Update:
    I believe that the issue WAS, running out of fuel.
    The tank had been cleaned numerous times, but when I filled it, I discovered a few pin holes in the front of the tank. It had some little spots of rust inside, so I decided to line the tank with Caswell’s tank epoxy.
    Upon removing the petcock, I noticed the reserve filter screen had some rust particles, which I believe were restricting the fuel flow. So, I sealed the tank, cleaned the petcock filters, and replaced the fuel line with clear fuel hose ( for visual inspection). The spare Igniter box came in, so I went ahead and swapped it.

    The fork seals had been leaking and I had previously ordered new seals and bushings.
    The parts were here, so I decided to rebuild the forks while I had it on the lift.
    While there, I installed some billet clip on’s to give me some adjustment for a better ride position.

    I just took it for a ride up the street, it has the noticeable hesitation/sputter at around 7k that most people have mentioned, but it clears up and smooths out and revs out great.
    This is the first time that I have ridden it.

    My impression so far: It revs to the moon, sounds really good, but I’m a bit disappointed in the power.
    My KR250 would outrun it. Next, I have to get it registered and I will be able to get it out on the road.
    Thanks to everyone who helped.
     
    • Like Like x 1
    • Winner Winner x 1
  15. DannoXYZ

    DannoXYZ Well-Known Member

    Messages:
    354
    Likes Received:
    216
    Trophy Points:
    248
    Joined:
    Sep 7, 2017
    Occupation:
    IT Manager
    Location:
    Mesa, AZ
    My Bike:
    Honda CB125TT, Kawi EX250F, EX250J race, Honda CBR250RR-MC19, NSR350R-MC21 VF500F, CBR600RR, VFR750F
    Might want to dyno-test to confirm AFR and power-output.

    My CBR250R MC19 was pretty anemic when first getting back on road. After having carbs professionally restored by Gordon @ https://customcarbservices.com , it ran A LOT better. Checking with wideband-O2 showed lean spot in mid-range and super-rich high-end. Ended up shimming needles 0.75mm and going down main-jets 1 size. Still super-rich in high-end at 10:1 AFR, but will put off downsizing mains again until I get on dyno. Looking to get MC22 exhaust with smaller tubing first.

    My sponsor Spears immediately downsized mains on my track Ninja 250 before dyno-tuning. After initial pulls, he downsized once more. That's with Tyga full-exhaust and free-flow intake. Ended up with +22% more power than stock. That's 22% more airflow than stock to match 2-sizes smaller mains. Still pig-rich @ 11:1 AFR.

    Nice bike BTW!!! :)
     
    • Like Like x 2
  16. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Wow! 22% is amazing.
    Fortunately,
    The Barber Vintage Motorcycle Festival is next week.
    There will be a mobile Dyno there. (Halls brothers)
    I plan to get it there and get a baseline run.
    Should give me enough information to start.
    I’ll take some shims, just in case. These carbs aren’t as easy to access as my other bikes.
    May take the KR too.
    Thanks
     
  17. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Well,
    Got the bike on the dyno, whopping 15 hp!
    Air/fuel ratio was 13:1 all the way through the rpm range.
    On the way home, it died at a stop.
    Restarted, then wouldn’t rev past 3000 rpm, even full throttle.
    I have parked it until I can set some time to investigate.
    Oh yeah, the KR250 got 41 hp at the wheel.
     
    • Bummer Bummer x 1
  18. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

    Messages:
    5,102
    Likes Received:
    3,472
    Trophy Points:
    1,148
    Joined:
    Dec 23, 2012
    Gender:
    Male
    Location:
    Thailand
    Home Page:
    My Bike:
    Yamaha FZR400 3TJ1, Honda MC22
    A compression test would be the first thing then.
     
  19. Sweeks

    Sweeks Active Member Premium Member

    Messages:
    50
    Likes Received:
    19
    Trophy Points:
    178
    Joined:
    Apr 5, 2020
    Gender:
    Male
    Location:
    Alabama, USA
    My Bike:
    1990 Kawasaki ZXR250R, 1984 KR250, 1973 Z1, 1972 H2, 1973 H1, 1973 Bighorn
    Compression test:
    #1=150 psi
    #2=125 psi
    #3=150 psi
    #4=125psi
    Interestingly, #1& #3 plugs were wet (fuel).
    #2 & #4 looked to be running clean.
    Checked the service manual, acceptable range is 143-218 psi.
    Thoughts ?
     
    Last edited: Oct 20, 2021
  20. ShaneP

    ShaneP Well-Known Member

    Messages:
    2,574
    Likes Received:
    1,101
    Trophy Points:
    798
    Joined:
    May 12, 2014
    Gender:
    Male
    Location:
    Yeppoon
    My Bike:
    Yamaha FZR250 speed bike, Yamaha YZ/WR250F, Kawasaki ZX2R, Honda VTR250, DR350 (x 3.5), a couple of prototypes and whatever else.
    I think their consistent afr reading sounds suspicious. But it is speculation. The wet plugs don't match the coil, so I can't blame that. Unless the leads were on wrong way around, but you sound too knowledgeable for that.
     

Share This Page