Umbau von Gt125r motor auf GT250 Motor

[Hawkonair]

Bike Model = : GT125R 2007

Hallo Zusammen,

Was brauch ich alles von 125 auf 250 umzubauen??

Hab gesehen, dass der 250 eine zusätzliche elektrische Kraftstoffpumpe hat, muss ich die auch umbauen?

Oder reicht es nur Motor und CDI von 250 zu nehmen?

Gruss

Hawkonair

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

Hi , If you don’t mind , would you be able to let us know what you were saying in English please?

[Hawkonair]

Hi everyone,

 

What all do I need to convert from a 125cc to a 250cc?

 

I saw that the 250cc has an additional electric fuel pump. Do I need to swap that in as well?

 

Or is it enough to just use the engine and CDI unit from the 250cc?

 

BR,

Hawkonair

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

If its an EFi 250cc , you need the full donor bike (EFi Tank, All electronics, Exhaust because it has lambda sensors , EFi airbox, EFi dash)

This is assuming you are using an EFi 250.

Otherwise if it is a carb model, upgrade your 125cc jets to 250cc one and keep using the 125 vacuum pump (that electric pump in picture is worthless = too many problems that’s why Hyosung used vacuum pump on all carb models after this)

[Hawkonair]

It is a 250 Naked Model from 2005 with Mikhuni Carbs.

I Read that 250 musst have a elektric full Pump…

I heard the 250 needs an electric fuel pump to keep up with fuel delivery at higher RPMs.

Can I use the vacuum pump, tank, and the rest of the setup exactly like on my 125cc?But doesn’t the 125cc have a narrower intake manifold with one of those nipples in it?

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

I need help

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

Are the intake hoses of the 125cc and 250cc carburetors on the cylinder head the same?

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

If I convert to vacuum, can I use the intake hoses from the 125? With the carburetor setup from the 250?

 

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

Hawkonair wrote:

If I convert to vacuum, can I use the intake hoses from the 125? With the carburetor setup from the 250?

Quote

Yes you can.

[Hawkonair]

Thx Marcel

Do I only need to swap the main jets, or do I also need to replace the pilot jets and other parts in the carburetor?

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

I also disabled the secondary air pump immediately.

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

I Found this

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

Use 250 jets pilots and mains, because of bigger pistons, or it will be lean and burn a hole in the piston.

Don’t worry about the vacuum pump, all 125 / 250 are using 650cc pump – Hyosung uses a 650cc pump on their 125/250 motors. So if a GV650 can use the vacuum pump, your 250 will never max it out.

Good luck!

[Hawkonair]

Should I only change the main jet and pilot jet?

 

Because according to Hyosung’s technical data, I also need to change the main air jet, needle jet, and starter jet.

 

I wanted to raise the needle and install a sports air filter.

 

I also have a 95 and a 98 main jet; would that work as an upgrade, or does it have to be a 95 and a 97.5?

 

Thanks for your help, and I’ll let you know how it goes.

 

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

95 + 97.5 Mains.
20 + 20 Pilots
And that’s it. Dont worry about other carb parts.

If using a sports filter, make sure its a K&N or BMC etc, as Hyosungs do not like “pod filters”, they will refuse to run correctly with no OEM airbox.

[Hawkonair]

I’ll use the 250’s carburetor setting, only the front main jet to 95 and the rear main jet to 98.

Can I use a 98 in the rear, or is a 97.5 strictly necessary?

I’m using a BMC air filter and will install a full Turbo Kit exhaust system.

 

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

98 is too much fuel, it will end up washing down your piston walls. 97.5 is max but it will be fine in 92.5 and 95 (factory setup) , so 98+ is overkill.

[Hawkonair]

The first carburetor is from the 125cc, while the second image shows the one from the 250cc.

Since I’m converting to a vacuum system, I noticed the 125cc carburetor has differences that the 250cc doesn’t. Do I need to use the 125cc carburetor body and install all the internals and controls from the 250cc into it?

Since I see this on the 125cc carburetor, I assume it’s also part of the vacuum system, right?”

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

If I take the caps from the 125cc carburetor and install them on the 250cc one, that should be enough, right? That’s the only difference.

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

Your just have older style carb, use the 125cc as it is updated. It has jet pump on the side. It is not critical , but helps a little bit on throttle that is all.

Coils = Same for all GT/GV carby models for 125 and 250cc. You will be fine. Otherwise, take 250 electrics and put it in 125 if you’re worried and keep the old 125parts for spare.

Service manual will tell you more on electrics if you want to check coil & stator resistance etc.

[Hawkonair]

It’s likely not necessary because it only activates with full throttle and doesn’t pump continuously; it’s probably just for priming before the first start.

Alright, if it’s not strictly necessary, I’ll just leave the 250cc carburetor in.

Installed the 250cc carb using 125cc intake hoses to maintain vacuum delivery.

Okay, if you say the electronics are all identical, including the coils and everything, then I’ll leave it just as it is.

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Hawkonair]

The bike runs only with the choke on; it accepts throttle, but stalls at idle without the choke.

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[♠️ M77]

Clean the carbs , check your jets , and you probably need to check engine compression to make sure its good.

[Hawkonair]

It’s running, just needs an oil change and I’m looking forward to the drive.

 

GT125R BMC, Full Turbokit GP, Carb Front 90 Rear 92.5

[Author]

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