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Help Missing 10 hp at 2KR

Discussion in 'Yamaha 250cc In-Line 4's' started by cornulio81, May 5, 2020.

  1. cornulio81

    cornulio81 Active Member

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    Hello Guys,

    May I have your opinion for my described problem, maybe I overlook sth.:

    My 2KR seems to ride ok, but the little punch I am missing.
    It revs up to the limiter, but not with the power it had in the past.
    The torque/power kurve seems ok till 14.000, but then there is especially from the 3rd gear on, not so much power.
    From 140 km/h it also accelaretes very chewy, with my 85kg I only reach 160-165km/h.
    In the past the Bike runs 180+ (On the German Autobahn ;))
    While accelerating e.g. in 6th gear, it runs ok till 14k - you feel also the incredible torque:crazypilot:,
    but after reaching 14k you feel an abrupt power loss. It revs further, but very weak.


    At a biker meeting there was a cheap dyno and I could let test the power output.
    Result was only 34hp. Plausible for how it runs, so anywhere has to be the failure.

    Diaphragms:
    -I changed them against new ones (ok, also a few years ago, but not 30^^) from Hyosung.
    They have 3 holes in the slide instead of two. I drove both, and didn't saw a difference, but at the end I closed the 3rd hole to be original.

    -Fueling:

    Carbs were cleaned very well. I had to, there were some resin in some jets, where supersonic wasn't able to clean and I had to clean manually. I also assembled a Litetek sealing Kit, very recommendable. I now ordered a fuel filter, I think it is still the first one (min. 25.000km inside:imtheking:) Maybe I am lucky and it was that. But it didn't getting worse, so let' see, has to be done anyway-

    Air Filter:
    I have fitted an K&N Air Filter due to the high price of an OEM Filter. I searched acc. the measures of the OEM Airfilter and found at K&N sth. (I think It was from a FZR400 model).
    Could it be, that the Airbox is extremely sensitive acc. the flow inside? Unfortunately I don't have the original one anymore. And I hadn't a precise before/after testing, because the bike stood over ten years in a garage, till I made anything new. I also tried to reduce the airfilter surface by ductape, but it was getting worse. Also the coldstart by choke, almost no idle, which is cause it should cold be better with less air.

    I also changed the rubbers between airfilter and carburettor since they were so hard, you couldn't fit sufficient anymore

    Leak Air:
    I tested for leak air by brake cleaner on the complete Inlet side, especially the inlet rubbers, but there is no response, tested on cold and hot engine.

    Valve clearance:
    i checked them about 10tkm before, they were all in the minimum range and I set them to maximum clearance.
    But this had no effect, so it has to be sth. which has a bigger impact like valve clearance.

    Ignition:
    Very Well, checking and maintaning regularly. But now while I am writing it came in mind, that I never changed the coils, and they are over 30 years old:oops:
    I have some from an FZR 600, should fit for a test?!

    Thank you for any ideas and have a nice Day :)
     
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  2. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    You seem to have covered everything! In this case, I would start with the air and fuel filters. I have had problems with fuel filters becoming restricted in a short time. If your tank is clean, try running without the fuel filter and see if there is any change.

    I would also suggest trying the old oem air filter or no air filter temporarily and see if there is any change.

    In my opinion based on your symptoms, the problem will be related to fuel/air flow. My gut says restricted fuel flow due to issues at high speed/rpm.
     
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  3. kiffsta

    kiffsta Senior Member

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    Can your dyno operator check your exhaust gases and see how it performing across the rev range ? It is great to know top power figures, but without the data to see what it is doing along the way , you will be clutching at straws

    I agree with Linkin, remove the fuel filter and test , no chnage, try removing the air filter and test again
     
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Compression figures please.
     
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  5. jmw76

    jmw76 Well-Known Member

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    When I tested my little CBR250rr track bike on the dyno, we started with about 32 bhp at the wheel. After playing with air filter, air box configuration and jetting we finally ended up with 42 bhp at the wheel. The main issue was that it was just running too rich.
    But as maelstrom said, do a compression test to get an idea how the rest of the engine is.
     
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  6. cornulio81

    cornulio81 Active Member

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    Hi,

    no, it was a a biker event with a dyno for the visitors. But I knew it before by feeling, that sth. is missing.
    I think a missing Airfilter will decrease usually the power due to bad airboxperformance, isn't it? Filter is cleaned & oiled.
     
  7. cornulio81

    cornulio81 Active Member

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    34hp was the power on the clutch with re-measuring the losses while spinning out the drivetrain in idlespeed.
    With the k&n Filter it should be more lean than with stock?! But Maybe there is any issue that could be run too rich anyway!

    Most Sport Yamahas are running too rich. Also my yzf750 are with complete new needles&tubes are too rich (fixed it a little bit with a dynojetkit). Maybe also a "german" jetting from Yamaha for more engine saftey, due to the possibility to drive legally a long time with high loads and topspeed, like on the "german autobahn" (I like to tell it in English:p)

    Yes, correct. I didn't do that cause it was directly after rebuild. before rebuild it was ok. But you are right, better I should do that.:thumb_ups: I hope I have this evening time for.
     
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  8. cornulio81

    cornulio81 Active Member

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    I will take following plan now to encircle the fault:

    1. Test drive w/o fuel filter (I hope I find a suitable connector) -->find out if too lean
    2. If 1. shows no effect, test drive w/o airfilter --> find out if too rich
    3 If 1. and 2. shows no or worse effect, compression test -->find out if I am screwd:party:
     
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  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Another thing with the K&N being oiled, i modified my original 3LN3 panel air filter, i cut the paper section out and used a cut down K&N element oiled it and fitted it to my bike
    This was during my carby tuning trying to get them running their best after rekitting the carby's

    I had trouble's with it running rich still, so degreased the air filter, washed it out and dried it then put it back in
    I had to play with the mixture screw's and got it running better (not as rich)
     
  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    What @jmw76 said. I have never seen a Japanese 4 cylinder running lean. They are always rich. Then their owners put bigger jets in them to make them slower and ruin their engines faster.
     
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  11. cornulio81

    cornulio81 Active Member

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    Good try! Usually the K&N Filters allow more airflow or in other words, have less flow restricition than OEM.
    But if the Air pressures and velocities are applied with the OEM Fillter, any other Filter will have a negative effect.
    Maybe in your case was too much oil? But this is also a good try. I think I will test it after testdrive w/o the filter, where I think it will getting more worse.
     
  12. cornulio81

    cornulio81 Active Member

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    You are right. Only possibility to run lean is with leak air after the carbs.
     
  13. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    A common thing with K&N and other oilable filters is that people don't read the instructions and over-oil the filters, hence running rich.
     
  14. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Definately not too much oil, i used less than K&N recommended
     
  15. cornulio81

    cornulio81 Active Member

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    I didn'nt found a suitable connector, so I will wait till I have a new feul filter, need one anyway.
    So, I came to do test Nr.2. for the first.
    Result:No change at high revs, worse at lower revs, but driveable. So the filter seems not to be the problem.
    I think i can do the compression test at the evening. Does anybody know the compression for cold and warm engine by heart?

    Thanks!
     
  16. cornulio81

    cornulio81 Active Member

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    OK, i am screwed.
    Compression test is showing following im bar (cyl 1-4):

    5,5 - 6,5 - 6,5 - 6

    Was done with cold engine, but without knowing the direct values, it's too much lost.
    I will Check the valve clearance first to be sure, is relative fast done.
    If they are in spec, i have to dig further.

    The engine has now 56tkms, so for this small engine with for the time high output, it's more than OK. But i am a little bit sad too, have this Bike for more than 21 years now

    Does anyone have experience, If in general at this model only the piston rings were worn, or maybe more?
     
  17. kiffsta

    kiffsta Senior Member

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    5-6 bar is about 70-90 psi , generally a compression test is done with the engine hot and the carbs off or held fully open.

    how do your plugs look ?
     
  18. cornulio81

    cornulio81 Active Member

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    Hi, here my plugs attached.
    IMG_20200505_201600416.jpg
    Yes fully Open throttle, i know.
    Usually there have cold ans warm values ( cold für Testing, If engine is not running). I will tomorrow test warm, today my son was sleeping already.
    The 4th Plug is a little bit brighter.
     
  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    So much for the 'rebuild'. What were the piston to bore clearances and what did you do to run in the new rings?

    Reading mixture on spark plugs is done right at the base of the ceramic, but pointless with low compression anyway.
     
  20. cornulio81

    cornulio81 Active Member

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    So, the rebuild was no engine rebuild. The Bike was Stores 10 years. This was 9 years before. Then i fixed every issue that was caused by the long storage. And mostly my Girlfriend drove since then 26tkm on it. 9 years before it was OK, reaching 180km/h. But getting worse now.
    Sorry If sth. was missunderstand. Sometimes i run against the language barrier (english ist not my mother speech)
     
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