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1987 Honda CBX250 Project

Discussion in 'Your 250cc Projects' started by Kerz, Oct 16, 2013.

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  1. Kerz

    Kerz Beginner level grinder :)

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    Hey guys,
    So I bought this bike which seems to be fairly rare and hard to get good parts for anymore. I would like to tackle a carb rebuild at first and slowly work my way towards an engine rebuild. It's a small 249cc RFVC 4-valve engine with a single carb. I do have some technical knowledge but I really want some opinions from some more experienced members on whether I should go ahead with it.
     
    Kerz, Oct 16, 2013
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  2. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    From what Ive been reading its just a dirtbike engine shoved in a sporty frame etc .... something other manufacturers did at the time also
    To me thats a good thing .... the CBX might be rare but I would think the XL/XR 250 the motor derives from is not.

    The carb will be a Mikuni or maybe a Keihin .... in other words not a Honda or wateva 'part' ...... and more than likely used in all sorts of other machinery (jetskis,ATVs etc)

    The biggest thing with carbs is cleaning them inside ..... if they are untouched for years they will be full of crud and have blockages in the jets and tiny passageways.
    If it needs o rings u can always match them up or make the larger float bowl ones.
    If we can find some detailed specs on the CBX or XL it will have the carb type etc to work off.

    If that info re the motor is correct then heres some parts schematics etc for the XL ...

    http://www.cmsnl.com/honda-xl250r-1985-usa_model7687/partslist/


    Whateva u do take pix before u dismantle , pix of the bits disassembled and keep everything sorted and labeled (in plastic seal bags ?) as what u remember when u pull something to bits may not be there if reassembly is months later.

    Theres plenty of experience here to help u along the way .


    Get the tools out! :aggressive:
     
    GreyImport, Oct 16, 2013
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  3. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    • Like Like x 1
    GreyImport, Oct 16, 2013
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  4. Phil

    Phil Senior Member Contributing Member

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    Phil, Oct 16, 2013
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  5. Kerz

    Kerz Beginner level grinder :)

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    Kerz, Oct 16, 2013
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  6. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    You mean like this?

    honda-xr250r-1987-australia-carburetor.gif
     
    GreyImport, Oct 16, 2013
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  7. Kerz

    Kerz Beginner level grinder :)

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    My Bike:
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    Sure do
    Like I said the CBF250 manual says the jets are #150 & #45
    The XR250R manual says the jets are #125 & #40

    Grey can you tell me difference between these numbers? Are they quick references to part numbers or are they sizes? I would be leaning more towards the XR jets for the CBX, they're the same year, engine and carb. Otherwise I hope the jets have numbers printed on them.
     
    Kerz, Oct 16, 2013
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  8. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    They are sizes ..... and yes they will be stamped on the jets.
    I would look at whats in the bike first just to compare...... they could have been changed of course and some bikes can be rejetted for different reasons.
    Carb jetting can be a curly subject ..... have a look online for some explanation on what does what.

    Sticking to a stock setup would be the go for starters ....thats of course if u can figure out what that is!
     
    GreyImport, Oct 16, 2013
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  9. Kerz

    Kerz Beginner level grinder :)

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    That's it! It's comin apart. Standby for pictures
     
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    Kerz, Oct 16, 2013
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  10. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Oct 16, 2013
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  11. Kerz

    Kerz Beginner level grinder :)

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    Kerz, Oct 16, 2013
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  12. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Good stuff .... that carby looks pretty 'clean' considering the age of the bike ....... give it loads of carby cleaner and compressed air in the jets and passageways is important .

    Was the bike running beforehand?
     
    GreyImport, Oct 17, 2013
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  13. Kerz

    Kerz Beginner level grinder :)

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    Do you think that compressed air through the jets is enough, the main jet seems pretty worn on the end. The bike was running good but the idle was a bit fiddly, besides I wouldn't think a carb rebuild wouldn't hurt it any. My main concern is the diaphragm piston, it's pretty dirty. In saying that there is no pitting on the piston and the carb is pretty clean. I'm yet to ring Honda about any new jets for pricing but hopefully I'll get to it this afternoon. BTW the main and idle jets were #125 and #35 respectively.
     
    Kerz, Oct 17, 2013
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  14. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    You are at an advantage as u have a single carb (as opposed to 4!) so 1 set of jets shouldnt break the bank.

    Most dealers dont want to know you when it comes to bikes of this age ...... also its a grey import and rare.
    Apart from that they will charge u a kings ransom.

    Best is to deal with someone who sells them direct , especially if you need some help.

    I think that kit from Sirius looks the goods to me .... it has the right jet sizes.

    Theres a ton of jets etc on ebay (always try ebay.com or .uk )

    http://www.motorcyclespareswarehouse.com.au/

    http://www.jetsrus.com/a_jets_by_carburetor_type/a_jet_kits_keihin_selection.htm

    http://www.showandgo.com.au/jet/jet.htm?jet_bf.html~mainFrame


    If the carb is apart for any length of time spray the diaphragm with silicone (http://www.supercheapauto.com.au/on...ray-300g.aspx?pid=135463&menuFrom=60503#Cross ) and stick it in a plastic bag / container so it doesnt dry out.

    While the carb is off check the carb to manifold rubber boot for cracks/leaks ..... and also whateva setup connects /seals the carb to airbox.
     
    GreyImport, Oct 17, 2013
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  15. Kerz

    Kerz Beginner level grinder :)

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    Well it's back together and running smoother than ever, sounds better and I re-adjusted the accelerator cables for better responsiveness. I'm very pleased with the end result. Thanks for all the tips Grey, some of those parts websites are pure gold. BTW thanks for the heads up on those dimple (JIS) screws, they were all over it. Now I'm looking to clean and inspect my chain, The guy at Honda told me you can scrub it with Kero and a toothbrush, then lube her up. Is there any truth to this.
     
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    Kerz, Oct 18, 2013
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  16. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Great stuff .... glad to hear that!

    Honda man is correct

    Are u going to take it off to do it? ..... does yours have a centre stand?

    While u are in that area have a close look at your sprockets ..... if things are badly worn u may need new ones and if so a new chain is recommended at the same time.

    Heres a new sprocket compared to a worn one .... worn one will have 'pointed' teeth

    Sprockets.jpg

    sprocket.jpg
     
    GreyImport, Oct 18, 2013
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  17. Phil

    Phil Senior Member Contributing Member

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    You can also grab a can of degreaser and spray the chain and get most of the crap off. Then hit it with some chain lube and your in business.:thumb_ups: Always good to have a clean and lubricated chain, peace of mind.:cool:
     
    Phil, Oct 18, 2013
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  18. Kerz

    Kerz Beginner level grinder :)

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    Well I went for I ride today with F1Dz and his '88 ZX250 goes hard, once I get above 4th on the CBX250 the torque is near non-existent. I would say even without looking at the sprocket it would be worn as i ticked over 50000km today. I don't know how long they should last but it's probably about time. My main concern is that if i replace the front and rear sprocket, with a bike that has next to no torque above 4th, and a top speed of about 150km/h (if that). Would it be worth changing sprocket sizes? Yes it does have a centre stand, I have to chock it up though to get the wheels off the ground.
     
    Kerz, Oct 18, 2013
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  19. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    The inline 4s of that era (FZR,ZXR etc) are known for their zip and are called screamers for a reason :D

    I do remember though while researching your bike it was mentioned about how the higher gears are pretty useless.

    Centre stands are a great asset so it will make doing the back wheel stuff alot easier ..... when I need more clearance with the Triumph I stick a big block under it so the stand legs land on it while raising it.

    Either count the teeth on each sprocket or look for a number stamped on it ...... Im no expert on 'gearing' but changing sprockets to give more acceleration and less top speed may help .... ?
    Of course what you need is the stock sprocket size and compare it to whats on it now , in case its been changed beforehand.

    Here we go ..... ( I got my sprockets from these guys )

    https://www.slipstreamperformance.c...bx250&osCsid=112408fa21c16c715a8352713a9acd48

    Says stock sprocket front 13t and rear 35t
     
    Last edited: Oct 18, 2013
    GreyImport, Oct 18, 2013
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  20. Kerz

    Kerz Beginner level grinder :)

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    I pulled all of the fairings off so I could inspect the wiring (I had a starter relay issue yesterday). Also now I've thrown the "all original" idea out the window and have come to terms with the fact that it's mine and it will look how I want it to.
    SO, here's what I have so far:
    1.Indicators I would like to change the rear stock indicators to something like this
    http://www.mcas.com.au/motorcycle-parts-indicators/barracuda-indicators-frecustom-chromea-led
    or this
    http://www.mcas.com.au/motorcycle-parts-indicators/barracuda-indicators-quadra-led
    2. I want to respray something like a gloss black with trimmed with red and gold (maybe pinstriped).
    3. New front shocks (Hopefully someone can help me with this one). They're really soft.
    4. Front 13t and rear 34t sprockets.
    5. Tear out the old airbox, re-position the battery and just have something like a chromed up pod filter as the intake.
    6. I would like the exhaust to be a bit brighter if possibly (sound), it's drones pretty hard.

    Any I/P from experienced members would be much appreciated.

    https://plus.google.com/photos/1180...s/5936352455471892593?authkey=CObfrbj8y_Tb2gE

    Also I will update my avatar as soon as it will let me :)
     
    Kerz, Oct 19, 2013
    #20
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