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

Discussion The ZXR250 flat spot / dyno tuning

Discussion in 'Kawasaki 250cc In-line 4's' started by Linkin, Nov 11, 2018.

  1. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    I got the chance to run my ZXR on the dyno at Ultimo TAFE on Friday. I still hadn't balanced or tuned the pilot mixtures properly since doing the top end, but I was keen to find out what was going on with the flat spot, as I haven't been able to fix it.

    Dyno's are a nice tool, my problem is that when cruising around at 60km/h in 5th (or 70km/h in 6th), opening the throttle results in a bog. If you then immediately repeat that, it revs cleanly. With the dyno we can replicate that, and found that it is actually a very rich spot. The AFR was down to about 9.5:1 at that point.

    The bike was also very lean at idle, varying between 13-15:1

    BMT0tkj.jpg

    Did two power pulls and ended up with 37.4HP with 2% atmospheric correction. AFR was 11.7-11.9, so a little on the rich side.

    lVojIRR.jpg
     
    • Like Like x 2
    • Agree Agree x 1
  2. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    I was advised that changing the air bleeds to larger ones would help, or I could adjust the emulsion tube needles, and possibly change the diaphragm springs.

    First thing I did was count and reset all the pilot mixture screws... it doesn't pay to do things in a hurry, because they were all over the place. Reset to 2.75 turns on all.

    I recently did the keyster kits and replaced the standard needles. Removed and inspected the keyster needles and found them to be wearing. I put the standard needles back in, they look to have a tougher finish (nickel plated?) and had no wear.

    Re-fitted the carbs and adjusted the synchronisation, which was all over the place after doing the top end. Now nicely balanced and running great again. Next stop: Dyno :)
     
    • Nice Work Nice Work x 4
    • Like Like x 2
  3. TonyZXR

    TonyZXR Active Member Premium Member

    Messages:
    302
    Likes Received:
    167
    Trophy Points:
    148
    Joined:
    Apr 17, 2018
    Gender:
    Male
    Location:
    New South Wales
    My Bike:
    GPX250, ZXR250A, ZXR250C
    Aren`t the air bleeds pressed into the carb body and can`t be changed , i was looking at how hard it would be to put zxr400 carbs on mine .
     
  4. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

    Messages:
    2,080
    Likes Received:
    1,154
    Trophy Points:
    823
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Location:
    Melbourne
    My Bike:
    Spada & VT250F
    The 32mm ZXR400 carbs require custom everything to graft to a ZXR250. Better off trying to find a set of B carbs (rocking horse poo).
     
  5. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    Aren't B/D models also 32mm? The outsite diameter must be the same if they are a bolt on fit.

    So if the air jets are press fit, that only leaves us jet needles to mess around with?

    @sharky didn't you have some adjustable needles you bought for one of your builds?
     
    • Agree Agree x 1
  6. TonyZXR

    TonyZXR Active Member Premium Member

    Messages:
    302
    Likes Received:
    167
    Trophy Points:
    148
    Joined:
    Apr 17, 2018
    Gender:
    Male
    Location:
    New South Wales
    My Bike:
    GPX250, ZXR250A, ZXR250C
    i think the air jet is smaller on the 400 carbs which is fine . could probably jet drill it to the right size. Only reason i wanted to experiment is that theyre so available and for $30. Yep model b carbs are 32mm too thats why . Only problem i see is fitting an airbox
     
    Last edited: Nov 11, 2018
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

    Messages:
    3,214
    Likes Received:
    2,257
    Trophy Points:
    923
    Joined:
    Dec 23, 2012
    Gender:
    Male
    Location:
    Thailand
    Home Page:
    My Bike:
    Yamaha FZR400 3TJ1, Honda MC22
    Do Keyster make the tuning kits for the ZXR? You will probably need to email them or find the Japanese only page. They make them for the MC22 Honda but the last time I looked they were not showing on the English page.
     
  8. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

    Messages:
    2,080
    Likes Received:
    1,154
    Trophy Points:
    823
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Location:
    Melbourne
    My Bike:
    Spada & VT250F
    The 400 head is wider, so if you get a set of carbs from a ZXR400 you have to "build/customise" them to fit the narrower 250 head. The trumpets on the 400 carbs are a plastic one-piece unit that you could cut up, but in the end it might be more trouble than it's worth. The B model had different gear ratios too, so might be hard to get the 400 carbs to work on a 250 without the right TCI and gearing. But, if you decide to go forward, I'll be watching with anticipation.
     
  9. sharky

    sharky Well-Known Member Premium Member

    Messages:
    480
    Likes Received:
    324
    Trophy Points:
    273
    Joined:
    Aug 5, 2016
    Gender:
    Male
    Occupation:
    daredevil
    Location:
    Tweed heads
    My Bike:
    kawasaki zxr 250c
    Yes the CVK 32s for a 250 & 400 have different airbox mounts, most cvk carbs are similar except for inlet spacing & airbox mounts. @Linkin those needles came out of an old set of carbs I got, I have never actually tried them out, there marked 76u & what is noticable is they have no taper at the tip. 20181111_145955.jpg
     
  10. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    Would you be willing to sell them to me?
     
  11. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

    Messages:
    2,080
    Likes Received:
    1,154
    Trophy Points:
    823
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Location:
    Melbourne
    My Bike:
    Spada & VT250F
    @sharky those needles don't look like ZXR carb needles. The C1, C2 & C3 run N76U needles and no ZXR needle I have ever seen has those funky height shim grooves (or whatever they are). But, my experience isn't comprehensive, so happy to be corrected.
     
  12. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    The jet needles on the FZR250's have those clips and grooves, they are used to meter fuel through the emulsion tube by raising or dropping the needle. The standard ZXR carbs aren't adjustable unless you shim the needles, which richens the mixture. I need to lean it off, so adjustable needles are needed.
     
  13. sharky

    sharky Well-Known Member Premium Member

    Messages:
    480
    Likes Received:
    324
    Trophy Points:
    273
    Joined:
    Aug 5, 2016
    Gender:
    Male
    Occupation:
    daredevil
    Location:
    Tweed heads
    My Bike:
    kawasaki zxr 250c
    I'm with you @Frankster I have had about 20 sets of carbs & there the first I have seen, they didn't come on a bike just a parts pile & I cant remember if they were A or C carbs either. @Linkin there yours mate, I'll be interested to see if solves your issues.
     
    • Like Like x 1
  14. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

    Messages:
    2,080
    Likes Received:
    1,154
    Trophy Points:
    823
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Location:
    Melbourne
    My Bike:
    Spada & VT250F
    I wouldn't compare a mikuni needle from a FZR to a Keihin needle from a ZXR. In my experience, Keihin carbs are more "robust" and will work even when they're not configured to their optimum settings. Putting those 76U needles in a Keihin will be wonderful to watch. Good luck.
     
    • Like Like x 1
  15. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    This is the bike after tuning it last weekend. I'm hopeful that the AFR numbers will be far better, and it will make more power. I've also cleaned the chain and sprockets because of all the recent rain, and friction is the enemy as always.

     
    • Like Like x 2
  16. banner001

    banner001 Well-Known Member Premium Member Contributing Member

    Messages:
    98
    Likes Received:
    135
    Trophy Points:
    223
    Joined:
    Mar 18, 2016
    Gender:
    Male
    Location:
    Nuneaton, UK
    My Bike:
    2x ZXR400, ZXR250 - Possibly...
    The air correctors are pressed into the zxr400 carbs too...but it is possible to heat the carbs and use an easy out to get the air correctors out, you then tap and use jets in them instead...I'll try and find the article
     
    • Like Like x 1
  17. banner001

    banner001 Well-Known Member Premium Member Contributing Member

    Messages:
    98
    Likes Received:
    135
    Trophy Points:
    223
    Joined:
    Mar 18, 2016
    Gender:
    Male
    Location:
    Nuneaton, UK
    My Bike:
    2x ZXR400, ZXR250 - Possibly...
    • Like Like x 2
  18. flea

    flea Well-Known Member Premium Member Contributing Member

    Messages:
    165
    Likes Received:
    112
    Trophy Points:
    248
    Joined:
    Aug 12, 2015
    Gender:
    Male
    Location:
    herberton qld
    My Bike:
    87 cbx250 / xl250 / 73 ..74..78 yam xs650 /zzr1100 / tdm850 /tt350 /zxr250c
    out of curiosity , where did you find the rack for the zxr ,was it built for the bike or did you have to adapt it , and thanks some intresting reading on carbs
     
  19. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

    Messages:
    3,697
    Likes Received:
    2,169
    Trophy Points:
    943
    Joined:
    Mar 18, 2014
    Location:
    Sydney NSW
    My Bike:
    '99 YZF-R6, '99 GSF250VY
    Genuine Ventura racks are available for C models on their website, I ordered it through my work with the part numbers off the Ventura site
     
  20. flea

    flea Well-Known Member Premium Member Contributing Member

    Messages:
    165
    Likes Received:
    112
    Trophy Points:
    248
    Joined:
    Aug 12, 2015
    Gender:
    Male
    Location:
    herberton qld
    My Bike:
    87 cbx250 / xl250 / 73 ..74..78 yam xs650 /zzr1100 / tdm850 /tt350 /zxr250c
    thanks
     

Share This Page