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Thread: Mods thread: Hyosung GT250R

  1. #61
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    If you skim the head (assuming the combustion chamber is in the head and not the piston) it will raise the compression. It is not a simple job becasue you can easily take to much taken off or not enough. Regardless, once it has been skimed, you will need to get it rejetted straight away. This is the same with the air filter.
    If you put a high flow air-filter on then you will get more air in the mixture. This will cause the bike to run lean which can cause detonations, which results in the pistons melting.
    Nothing wrong with polishing the head. Just make it so thats a smooth flow, but don't actually polish it. It needs a semi rough finish to help mix the fuel and oxygen.

    Personally i'm not going to bother doing any of this to my GT250R. But good luck to anyone that gives it a try
    While you sit there liking things just cos' everyone else does, I'll be standing up here keeping it real.

  2. #62
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    Quote Originally Posted by Fub@r View Post
    My problem is my accountant (aka wife) wont let me upgrade at this time. Have a mortgage to pay. Although did find a nice SV650s

    Anyway, I have semi debaffled and was thinking over Xmas I might do the polishing.

    Whats the cost to do a skim? And mod the air filter?

    Once these are done, I then get the carbs rejetted?
    Oh mate, i wouldn't skim the head, i mean, lots of effort, easy to fuck up and if you run lean for to long, shit starts to melt.

    You can have either performance or reliability

    Seriously, the most you would want to do is a polish, free flow pipe, pod filter/airbox mod, carb jet

    Get the sand paper out and work out all the burs and roughness in the ports

    Then give the bike to warren with the standard air box, hand him the pod and say "jet it for this." That way, when you get the bike back, it will go like stink and not melt anything.

    Dont do major work, i mean, seriously, your just gonna get a big bike in the next two years anyway

  3. #63
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    Quote Originally Posted by Weaver View Post
    Nothing wrong with polishing the head. Just make it so thats a smooth flow, but don't actually polish it. It needs a semi rough finish to help mix the fuel and oxygen.
    um, what? The carb mixes the fuel and the oxygen. The reason you polish the ports is to aid flow into the combustion chamber. The flow is increased as there is less friction between the fuel/air particles and the port surface.

    It stops shit sticking pretty much, nothing more annoying than sticky shit

  4. #64
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    Quote Originally Posted by FilthyLuka View Post
    your just gonna get a big bike in the next two years anyway

    I need your accountant

    Rejet and polishing sounds like me

  5. #65
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    Quote Originally Posted by Fub@r View Post
    Rejet and polishing sounds like me
    Good man! Will be willing to give you a hand with that polish, still have a few sheets of unused sand paper of varying grades around here somewhere... PM me if you wanna get it done in january some time...

    You would be suprised at how rough engines come outta the factory. All bumpy and not shiny and stuff, ah you'll see.

    Oh, and merry fucken christmas you hyosung riding mod monkey!

    BAH HUMBUG!

    Denis

  6. #66
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    Quote Originally Posted by FilthyLuka View Post
    Good man! Will be willing to give you a hand with that polish, still have a few sheets of unused sand paper of varying grades around here somewhere... PM me if you wanna get it done in january some time...
    Heya, I'm quite keen to get mine polished as well. Perhaps we could make an event of it?

    After all there's nothing like having someone stand behind you and say "umm... I'm pretty sure you've mounted that backwards..." to make you glad you didn't try it all on your lonesome.
    "I have this really bad problem with not finishing my..."

  7. #67
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    Quote Originally Posted by EnzoYug View Post
    Heya, I'm quite keen to get mine polished as well. Perhaps we could make an event of it?

    After all there's nothing like having someone stand behind you and say "umm... I'm pretty sure you've mounted that backwards..." to make you glad you didn't try it all on your lonesome.
    haha, yeah that happens. I got real pissed off at my new battery for blowing fuses all the time... turned out the leads were the wrong way around, god fucking damnit...

    But yeah, i dont have much experience with hyosung gt series but two extra hands/eyes never hurt!

    Ill be keen, sort it out, go on, do it.

  8. #68
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    Quote Originally Posted by Fub@r View Post
    I need your accountant
    single mate, no accountant for me! #sigh#

  9. #69
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    Quote Originally Posted by FilthyLuka View Post
    um, what? The carb mixes the fuel and the oxygen. The reason you polish the ports is to aid flow into the combustion chamber. The flow is increased as there is less friction between the fuel/air particles and the port surface.

    It stops shit sticking pretty much, nothing more annoying than sticky shit
    Tis what I was told by the engine reconditioner that built a 1600 X-flow motor up for me. He said that the carb doesn't completely mix the fuel and that a highly polished intake (so smooth and shiny that its almost chrome like) doesn't assist the mixing process.
    But hey, what ever floats your boat.

    Time to open some christmas presents (hopefully all bike related)
    While you sit there liking things just cos' everyone else does, I'll be standing up here keeping it real.

  10. #70
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    Personally I'd flag the pod filter (filer directly attached to the carb). These were absolutely fine in the 80's when an airbox was just something the factory stuffed on the end of a carb between the frame rails. On any modern bike the airbox now gets a lot more attention re size inlet etc. A free flow filter for the stock box, pipe and carb settings will do the trick IF preformed by someone who knows what they are doing.

    Without sounding like a arse - the GTR250 is a nice bike, however its never going to set the performance world on fire, and at the end of the day, well its a 250. As you will no doubt get a larger ride in the future (6 months of begging at least) I'd leave the engine alone apart from a pipe if you are after a bit more noise (and lets all face it if it sounds louder it feels faster) and concentrate on personalising other aspects.

    Why - for no other reason than resale value - if you've fucked with the engine a lot a shop will not be very interested in trading, ditto private buyers. Bling can be easily removed and stock bits returned if so desired (sell bling on Trademe or add to the next bike).

    Thats what I do - each stock part thats replaced is popped in a box 'just in case'. I sold a bike I'd had from new for 23 years a couple of years ago - the box of parts that went with that was bloody heavy!

  11. #71
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    Quote Originally Posted by Weaver View Post
    Tis what I was told by the engine reconditioner that built a 1600 X-flow motor up for me. He said that the carb doesn't completely mix the fuel and that a highly polished intake (so smooth and shiny that its almost chrome like) doesn't assist the mixing process.
    But hey, what ever floats your boat.
    and he was right. you want inlets smooth not polished. keep to 80 grit or less. exhaust ports can be polished.

    good luck

  12. #72
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    Quote Originally Posted by FilthyLuka View Post
    Oh mate, i wouldn't skim the head, i mean, lots of effort, easy to fuck up and if you run lean for to long, shit starts to melt.

    You can have either performance or reliability

    Seriously, the most you would want to do is a polish, free flow pipe, pod filter/airbox mod, carb jet

    Get the sand paper out and work out all the burs and roughness in the ports

    Then give the bike to warren with the standard air box, hand him the pod and say "jet it for this." That way, when you get the bike back, it will go like stink and not melt anything.

    Dont do major work, i mean, seriously, your just gonna get a big bike in the next two years anyway
    Thats some good advice.

    Quote Originally Posted by Weaver View Post
    Tis what I was told by the engine reconditioner that built a 1600 X-flow motor up for me. He said that the carb doesn't completely mix the fuel and that a highly polished intake (so smooth and shiny that its almost chrome like) doesn't assist the mixing process.
    But hey, what ever floats your boat.

    Time to open some christmas presents (hopefully all bike related)
    And he was right. FL has covered that back up the thread a ways.

    Quote Originally Posted by 325rocket View Post
    and he was right. you want inlets smooth not polished. keep to 80 grit or less. exhaust ports can be polished.

    good luck
    Yep. Once you get them open you'll see there's lots to tidy up, tags & dags, before you get close to a mirror finish. I belive we are using "polish" in the head work sense not meaning that it it a polished finish. Different things.
    I'm selling my new riding gear!! Only worn a few times get a deal Kiwibikers!!
    http://www.kiwibiker.co.nz/forums/sh...53#post1414653

  13. #73
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    Thats what I was saying initially Pancakes. That it needs a semi-rough finish and an actually polished finish
    While you sit there liking things just cos' everyone else does, I'll be standing up here keeping it real.

  14. #74
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    Quote Originally Posted by Pancakes View Post
    Yep. Once you get them open you'll see there's lots to tidy up, tags & dags, before you get close to a mirror finish. I belive we are using "polish" in the head work sense not meaning that it it a polished finish. Different things.
    Ah, sorry weaver, yes you are right, you dont want a mirror finish. I thought you meant don't even go over it with a sanding roll and leave it after a grind out with a carbide bit...

    Anyway, on a similar note. There is a guy in the USA (ill see if i can find a link and post it up) that actually found a way to tap (read thread) the ports. The idea is, that when a droplet of un-vaporised fuel hits the thread in the port wall, it splatters off into lots of small drops that easily vaporise... To bad im not a good enough metal worker or i would try this... Would be nice to see a dyno read out for it and see if there is actually any improvement

  15. #75
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    Quote Originally Posted by EnzoYug View Post
    That's exactly what I did - only a little neater. Didn't actually 'Cut" the wire, just removed it from the plug and insulated it. If anyone wants to do this but is worried about getting the wrong wire try this:


    Hyosung GT250/R 2006/7 (NZ new imports)
    1. Open up the seat.
    2. Un bolt the CDI unit. (small black brick next to the relays)
    3. Disconnect the Brown plug from the CDI. BE GENTLE.
    4. Get a very small Alan key - preferably one that will fit into on of the circular holes in the 'male' end of the brown plug.
    5. Locate the Green/Blue wire.
    6. This wire should be in the same position as in Pancakes photo - if it is in a different position DO NOT REMOVE.
    7. Use the alan key to carefuly push the copper contact out of the plug. It should pop out the other side with the wire, blue plastic bung, and copper contact all in perfect condition.
    8. Tape up the end of end of the copper contact VERY thoughly with electrical tape. If you have some kind of plastic insulation to cover it as well I suggest using that.
    9. Tuck the loose wire back into the loom.
    10. Reattach the CDI.
    11. Power up the bike but DONT start it. Check all your lights work, and check the digital dash if you have one.
    12. If everything works fine continue - if anything has stop working then stop here - you've fucked up.
    13. Fire up the bike. Let it idle. Listen for anything odd - firing on one cylinder etc... normal? Good!
    14. Test the kill switch. If it doesn't work, you fucked up.
    15. Everything works go ride the bike. You should notice a VERY smooth power curve now.

    Extra for experts: Go buy a nice big exhaust, or get yours debaffled. Then get a new air filter, then get it re-jetted. (being cheap and not getting the re-jetting will fuck your bike in the long run) Enjoy the most powerful Hyobag on the block.
    Just have to say big ups to you, just did it to my bike and man what a difference it has made, no more flat spots and take off is alot faster and better

    Cheers EnzoYug

    Oh and bling on its way
    Lock the doors and close the blinds
    We're going for a ride

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