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. 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
    leak down test to confirm.

    however given the age of the bike, I'd bed the rings are worn out and valves not sealing.

    I did new rings, bore measure (ok) and hone, cylinder head cleanup and lap the valves, 16 new shims and new chain/tensioner.
     
  2. 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
    Coils correct, 1&4, 2&3.
    I actually thought (hoped)coils, but doesn’t make sense that #1 would be wet and #4 looks good.
    I’m on the fence about the compression results. I checked with engine cold, manual says warm engine.
    Didn’t do a leak down test, but if it were that bad; you would think I would see some oil deposits on the plugs or smoke from the exhaust.
    It ran smooth with no miss fires except for the big bog.
    Now it won’t rev past 3k rpm, even full throttle.
    I don’t know if they are related.
    The odometer has 35k km. So, I guess it’s got some wear.
     
  3. 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
    do you have any compression numbers?
    That’s what I was thinking that I would do.
    If I need pistons, I haven’t found any.
     
  4. 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
    Those numbers sound fine for a test. The combustion chamber volume is only about 5cc so what compression gauge is not going to show a lower value due to the hose/connector etc? I would suggest, none.
    The AFR value is odd. Owners do stupid things like drill out their main jets in their eternal quest to "fit big jets", so they can destroy their engines and make their bikes slower. The other place that fuel can come from is the choke circuit but 13:1 is not that rich.
    Did your 30mm carbs arrive yet? Once you can drop them on you are only left with the spark issue.
     
    • Agree Agree x 1
    Last edited: Oct 20, 2021
  5. 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, I have the carbs. I will probably get those on and see what changes.
    I had considered replacing the coils with coil-on-plug at some time in the future. It seemed like a good upgrade. This may be a good time, while I have in its disassembled state.
    Also need to order some spark plugs. Do you have the link that describes which coils are preferred?
     
  6. 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
  7. kiffsta

    kiffsta Senior Member

    Messages:
    9,066
    Likes Received:
    6,872
    Trophy Points:
    1,168
    Joined:
    Aug 7, 2010
    Gender:
    Male
    Location:
    Brisbane
    140psi per pot is acceptable , it would be interesting to warm her up , pop the plugs out and carbs off me do the comp test again.

    a leakdown test would be beneficial at this time to see what’s going on
     
  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
    4x ninja 300 coils have the correct resistance. You wire up 1 and 4 in series and then 2 and 3 in series using the original harness connections. You will need to build the rest of the wiring between the coils. It's not hard with the correct connectors, pins and crimping tool.
     
    • Like Like x 1
  9. 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
    Compression looks good, I wouldn't worry about that at all.
    Did you get a dyno-chart with AFR plotted on it? I'm highly suspicious if this dyno somehow gave you AFR reading of 13:1 across board; no carbed bike ever has flat AFR like that, much less that lean!

    Without buggered AFR around 7000rpm, that rules out fueling as issue on your stumble. Again, highly suspicious. Assuming we can trust AFR from dyno.

    1. Inspect needle-jets that slide-needles go into. Are they perfectly tubular internally? Or do they have taper on one end?

    2. Can you post photo of slide-needles? thx

    3. measure power to all coils, are they all same as battery voltage?

    4. with power ON, measure for power on activation line from CDI to coils. What's voltage?

    Are you familiar with wideband O2-sensor kits with datalogging? I find them extremely helpful because you can do WOT runs without worrying about staring at tiny AFR gauge. Then download data to PC later and analyse AFR in 100rpm increments.
     
    Last edited: Oct 21, 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
    Got these today
    C0E6192C-9FE7-4387-9232-31A5C9A45575.jpeg
    While I have it disassembled, I’m going to do the cop upgrade.
    Probably take it for a spin, see how it goes.
    I have the 30mm carbs built and ready.
    I’ll install those and then evaluate.
    I fully expect to put the Tsukigi exhaust system back on at some point, which brings me to the 02 sensor bung question.

    Dannoxyz.
    “Are you familiar with wideband O2-sensor kits with datalogging? I find them extremely helpful because you can do WOT runs without worrying about staring at tiny AFR gauge. Then download data to PC later and analyse AFR in 100rpm increments.”

    I have not used one, but have considered it.
    I don’t mind investing in one, but if I get one, I would like to be able to use it on my other bikes.
    Most of my other bikes are 2 strokes, not keen on bungs into all those expansion chambers.
    Do you have a particular brand/model ?
    It would be nice to have some way of temporary sensor connected to the exhaust.
     
  11. 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
    I've used these all-digital wideband-O2 kits for about 20-yrs. http://techedge.com.au/ Fully-digital, even output to external-gauge is digital vs. analogue like most others on market. Many Porsche engines has been destroyed by Innovate LM1 which doesn't even have reference-voltage for their analogue output to gauge, thus gauge reads different AFR depending upon battery-voltage.

    Originally got basic DIY kit with onboard-memory. Recently picked up newer kit. http://wbo2.com/2y/default.htm Really handy because they're self-contained units, don't need ECU or laptop. Hit button to start datalogging, take it out on track. Usually memory will record AFR, RPM, speed, TPS for about 10-laps, more than enough. Then come back and download data for analysis. I usually buy sensor itself separately. Bosch VW wideband O2-sensors can be had for about $40.

    Without bung, I suppose you can attach sensor to small hollow-pipe to protect wiring and shove it down exhaust. Clamp pipe to edge of exhaust outlet?
     
    • Informative Informative x 1
    Last edited: Oct 28, 2021
  12. 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
    Back again. I haven’t spent any time on the bike for a while.
    Installed and synchronized the second set of carbs.
    Also, converted to cop coils and iridium plugs.
    Starts and revs smooth, seems perfect.
    As soon as it reaches operating temperature, it dies.
    Upon restart, it will not rev, even at wide open throttle.
    Let it sit and cool, then it starts and revs perfect.
    This is repeatable.
    It did this same with the rebuilt original carbs and original coils.
    I swapped a cdi box with no effect.
    Anyone know of something that is heat affected that would cause this?
     
  13. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

    Messages:
    4,289
    Likes Received:
    2,504
    Trophy Points:
    918
    Joined:
    Oct 6, 2016
    Gender:
    Male
    Location:
    Albury 2641
    My Bike:
    1987 Yamaha SRX250, Honda 1974 SL125 K1, 2022 Triumph Tiger Sport 660
    As @Linkin mentioned quite a few posts up... Compression, Valve clearances.
    Basically as your engine gets hotter everything expands and there isnt enough compression to keep it going... Well that would be my guess.
    Dont bother with a compression test, try a Leak down test.
     
    • Agree Agree x 1
  14. Frankster

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

    Messages:
    3,980
    Likes Received:
    2,208
    Trophy Points:
    923
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Occupation:
    Gardener
    Location:
    Tasmania
    Home Page:
    My Bike:
    Spada, VT250F & ZX2R
    Set the fuel petcock to PRI and see if that helps. There may be an issue with fuel supply that's masking itself as a heat-related problem, so if PRI setting doesn't work, try feeding fuel to carbs directly via an external supply.
     
  15. 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
    The OP mentioned fuel supply as a potential issue earlier. Reading back on the posts, the constant 13:1 AFR and 15HP on the dyno lends credence to that... So potential causes... everything in the fuel system.

    Tank (Rust/water)
    Petcock (blocked/bad diaphragm)
    Lines (Old, kinked)
    Filter - if any (Flow restriction / incorrect filter type)
    Carbs - fuel inlet, internal fuel passageways, float seats/o-rings, float needle, jets.

    I know the OP is meticulous, but have you checked the mesh screens on the back side of the float seats? The seats are retained with a screw, remove that, pull and twist around the outside of the seat to remove them. Replace the seats/screens and blow out the fuel passageways.

    Best way to test where the problem may be is to remove the tank and run an external gravity feed bottle. Running the tank on prime is a good way to test if the diaphragm is bad (check the vacuum lines for fuel as well) and if your float seat o-rings/float needles are sealing (it'll flood if they're no good).

    If it were my ZXR I would still set all the clearances to largest specification and replace the cam chain/tensioner, unless you know they have been done. My tensioner lasted about 10,000km before showing signs of wear. Tiny chain and bad tensioner design.
     
    • Like Like x 1
  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
    Back to this problem.
    I have decided to disassemble the top end and inspect.
    Firstly, cylinder wear is at the max of factory specs.
    Absolutely no oversized pistons to be found.
    So, the pistons are in really good condition.
    I am getting the cylinders Nikasil plated and honed to min. factory specs for piston-to-cylinder clearance.
    I’m using the standard piston rings that I got from aliexpress.
    The cylinder head is disassembled and it appears that I need new valves.
    I have found Chinese replacements, but really don’t want to use them if I can find good quality replacements.
    Has anyone used ‘C’ model valves in an ‘A’ ?
    Has anyone here found any good quality valves ?
    There’s a shop in West Heidelberg, Australia called : motorcyclespareswarehouse
    That lists some for the ZXR250 that are made in Japan.
    Anyone know of them?
    I would very much appreciate your help,
    Thanks, Shane
     
    Last edited: Dec 13, 2022
  17. 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
  18. Justin_P

    Justin_P Active Member Premium Member

    Messages:
    1
    Likes Received:
    0
    Trophy Points:
    165
    Joined:
    Jul 18, 2020
    Gender:
    Male
    Location:
    Wodonga
    I've purchased the valves you are referring to from motorcycle spares warehouse, they are made by TKRJ in Japan

    https://www.tkrj.co.jp/product/m-engine-valve.html

    I bought a whole set for a top end rebuild which is still in progress.
     
  19. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

    Messages:
    10,914
    Likes Received:
    6,709
    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
    Yes they are fine to deal with .... Ive bought from them a few times via their website .... currently have an order from their ebay listings

    motorcyclespareswarehouse.jpg
     
    • Agree Agree x 1
  20. Frankster

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

    Messages:
    3,980
    Likes Received:
    2,208
    Trophy Points:
    923
    Joined:
    Nov 19, 2013
    Gender:
    Male
    Occupation:
    Gardener
    Location:
    Tasmania
    Home Page:
    My Bike:
    Spada, VT250F & ZX2R
    Hi Shane, those valves are fine. They weigh a tiny bit less than the original valves. Most of the parts Motorcycles Spares Warehouse stock are Japanese or from the original manufacturer e.g. their ZXR250 Head Gaskets are made from the original Kawasaki 'tool' but by another company who has taken over making them. I buy lots of stuff from these guys and they're honest and fair people.
     
    • Like Like x 1
    • Agree Agree x 1
    • Informative Informative x 1

Share This Page