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Help Advice needed on what carb parts to replace

Discussion in 'Honda 250cc In-line 4's' started by sloegin, Dec 17, 2019.

  1. sloegin

    sloegin Active Member

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    My Bike:
    CBR250RR L, RGV250 VJ21, GSX1300RY turbo
    I’ve pulled the tank and airbox off to investigate the poor starting on my MC22.

    Whilst I am in there what parts on the carbs as a minimum should I look to change to prevent problems in the future?

    From what I have read the carb. insulators go hard and crack so I should do those.

    I am going to check that the jetting is suitable for the current set-up using this guide - http://mootavic.olilolo.com/mods/tune.html

    What else? Are there any other seals/o-rings/gaskets etc. which have a history of problems?

    Thanks in advance.
     
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    IMHO
    First and most importantly, check the compression. Rings are never going to last long in an engine that does such high rpm.
    • Check valve clearances - I would set them at the largest clearance
    • Replace all the seals and o-rings in the carburettors (including airbox seals). Do you really believe they last thirty years?
    • Check diaphragms
    • Check float valves
    • set the jetting and needle position to standard
    • synchronise idle settings with Morgan Carbtune, or mercury gauges.
    • set pilot mixture by ear, failing that, to factory setting, or by varying from factory by 1/4 turn at a time and seat of pants
    • replace air cleaner element if needed
    Without extensive documented evidence, and my own confirmation, I would ignore any advice to change the jetting.

    Cheers
    Blair
     
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  3. kiffsta

    kiffsta Administrator Staff Member Contributing Member Dirty Wheel Club

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    Use oem Insulators , the Chinese ones are rubbish and crack
     
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  4. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Without any dyno chart proof I can see a lot of HP lost in this dribble.
    Do as Malestrom says first and start with checking compression and stock jetting and don't under any circumstances use 'pod' filters with your CV carbs.
     
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  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    https://litetek.co/Carb_Kit_Honda_CBR250RR_MC22.html


    Carburettor Synchronisation (max difference) : 40mmHg
    Carburettor ID Code (Keihin):
    CBR250(F) : VG01A
    CBR250R(H) : VG03A
    CBR250R(J+K) : VG05A
    CBR250RR(L+N) : VP20A
    CBR250RR® : VP20B
    Carburettor Throat Diameter :
    CBR250(F) : 25mm
    CBR250R(H) : 27mm
    CBR250R(J+K) : 28.5mm
    CBR250RR(L+N+R) : 29mm
    Float Heights (When measured at 30o or needle valve seated and spring NOT compressed):
    CBR250(F) : 7mm
    CBR250R(H) : 7mm
    CBR250R(J+K) : 8mm
    CBR250RR(L+N+R) : 13.7mm
    Carburettor Jet Sizes :
    CBR250(F) ;
    Main Jet : #85
    Pilot Jet : #35
    CBR250R(H);
    Main Jet : #88
    Pilot Jet : #35
    CBR250R(J+K);
    Main Jet : #85
    Pilot Jet : #35
    CBR250RR(L+N);
    Main Jet : Cylinders 1+4 : #105
    Cylinders 2+3 : #102
    Pilot Jet : #35
    CBR250RR®;
    Main Jet : Cylinder 1+4 : #112
    Cylinder 2+3 : #110
    Pilot Jet : #35
    Carburettor Pilot Screw Mixture Settings (Stock Air-Filter,Exhaust,Ports,Jets)
    CBR250(F) + CBR250R(H): 2Ѕ screws
    CBR250R(J+K) : 1 5/8 screws
    CBR250RR(L+N) : 1 3/4 screws
    CBR250RR® : 2 1/8 screws


    https://2fiftycc.com/index.php?threads/honda-cbr250rr-mc22-specifications.2521/
     
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    Last edited: Dec 17, 2019
  6. sloegin

    sloegin Active Member

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    Thanks for all the advice. I’ll start with the compression check as I had overlooked that.
     
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