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Help Air filter/carb upgrade GB250

Discussion in 'Honda 250cc Singles' started by EvanVT, May 21, 2017.

  1. EvanVT

    EvanVT Member

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    Hello all,

    I'm considering getting some aftermarket parts for my 1996 gb250 (single carb) and was wondering if anyone had recommendations, does k&n have an air filter that would fit this bike? Is it worth upgrading the carb? The stock carb is a keihin pwk 28 I believe. Has anyone played around with their set up?

    I'll leave the look stock mostly, but I'd like my engine to be performing as well as it can be.

    IMG_20170425_154356.jpg
     
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  2. Murdo

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

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    Cannot help you with a K&N filter, but to put a bigger carb onto a stock engine will be a waste of money.
     
  3. Wozza

    Wozza Active Member Premium Member Contributing Member

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    There is a k&n filter for the gb250
    http://www.ebay.com.au/itm/WM-K-N-P...744357?hash=item25d692f1e5:g:t0YAAOSwe7BWusG4
    You have to be careful that the aftermarket filter doesn't block or disrupt air flow to the front carb ports(most do). Also the stock carby doesn't have needle adjustment slots so you will need to shim it up a bit at the very least..To do it right you will need to rejet slightly richer.....I ended up with this kit
    http://www.ebay.com.au/itm/KEYSTER-Carburetor-Fuel-Adjustment-Kit-HONDA-GB250-CLUBMAN-/162496108053?
    The kit has mixed reviews mostly bad :) but it appears to be fine if you use all the matching parts from the kit and not mix and match with stock bits.....
     
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  4. EvanVT

    EvanVT Member

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    I was thinking of bigger but maybe a different/better brand like Uma.
     
  5. EvanVT

    EvanVT Member

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    This kit is got the single carb models?
     
  6. Murdo

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

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    Depends on what you want to do.
    Do you want economy or performance?
    For economy make sure the engine is to manufacturers specifications.
    For performance fitting of just a bigger carb and stubby air filter 'may' gain some increase at max revs, but most loose at all other revs. To do it properly will require planned work on the engine internals to increase the efficiency of the air flow, eg porting, cams changed, cam followers, larger valves, valve springs, exhaust, bigger cylinder bore, engine balance, etc. This then may have enough flow to need a bigger carb.
     
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  7. EvanVT

    EvanVT Member

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    Well I don't want to do a total overhaul on this bike, I live in a congested city and my GB doesn't seem to have the infamous GB acceleration, so I thought a little fine tuning of the carb and air intake would give me a little more pep without sacrificing economy.
     
  8. Murdo

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

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    This is the way I would go.
    Have the valve clearances set correctly (as these will cause a loss of performance if not within specs).
    Fit a new spark plug?
    Change the air filter (standard in the airbox, (airboxes give torque)) for an oiled foam type.
    Fresh oil and filter.
    Change the front sprocket for one or two teeth smaller (will give better acceleration with slight loss of top speed).
    MAYBE, go up one size on the pilot jet.
     
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  9. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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    Yea if youre in traffic all the time a sprocket change will give u some zip
     
  10. Wozza

    Wozza Active Member Premium Member Contributing Member

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    Yep part number FH-5052N is for the single carbed bike....well its the one Im using :D
     
    Last edited: May 22, 2017
  11. Wozza

    Wozza Active Member Premium Member Contributing Member

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  12. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    How many kms has your bike done? Depending on mileage some of your carbs parts such as needle and emulsion tube may have worn. Could be something to look at
     
  13. Snod Blatter

    Snod Blatter Member Dirty Wheel Club

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    The only way to go (in my opinion) would be a flat slide carb, probably a Mikuni TM though a seemingly well kept secret is that the CRF250s (and 450s) use a Keihin FCR, yet you can usually pick them up used for not too much money.

    Fitting a pod filter (K&N or otherwise) is normally a bad idea if you're putting it on a CV carb, the movement of the open air can unsettle the diaphragm and it won't work all that well - CV carbs really like an airbox. Of course if you change to a slide carb this is less of an issue, though pod filters don't filter as well as the usual paper filter you'll find in an airbox..
     
  14. Andey44

    Andey44 Member

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    A little off topic, but related, what’s the jetting on a stock carb?
     
  15. Andey44

    Andey44 Member

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    Oh found it:
    Pilot 40
    Main jet 130
     
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  16. Andey44

    Andey44 Member

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    Anyone know if it needle jet is suppose to have a washer under it?

    It’s between the needle and the round slide it sits on.

    Took mine apart to clean it and found a small washer, but the manual doesn’t show one

    D7F4C2F9-1342-45A8-9778-0DF710A812DB.png
     
  17. Murdo

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

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    The washer would be there to lift the needle and make the mixture slightly richer.
    If it ran well with it there then leave it on needle.
     

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