Reply To: Need help with hyosung GT125 P
Welcome to the forum!
Sorry to hear about that but we have faith as the engine is indeed alive 🙂
If you have an Amazon account, get USPRO compression tester or get a mobile mechanic to come over with his compression tester (don’t matter if its for a car, it does the same thing)
Make sure the bike is 10mins hot, then take the spark plugs out , both of them.
Put compression tester in one of the cylinders , eg. Cyl 1 is front engine spark plug hole. Put it there and hard.
Use a “METAL” rod with a curvy rubber tip , dont use a flexi hose because they are known to give false positives sometimes.
Twist throttle to full throttle, then hold it there. Crank the bike for 5 seconds ish max.
Get readings and report back .
We tend to always check engine compression of bikes before address other parts such as carb, coils, electrics and all that comes with it.
The engine is the main key to check to see if its actually healthy
Also, it helps to check valve clearances (if you can or mobile mech?) = Tight or loose clearances make it hard to run right no matter how tuned up the bike is.
It helps to keep fuel lines around 7-9mm max. 10mm is a little overkill to be fair and vacuum lines should be around 5-7 max.
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Sometimes , with the 125cc bikes, half its starting issues or idling issues are a result of the inlet manifolds , it is of the utmost importance to take them off (becareful, rusty bolts!) and visually inspect them.
Under the inlet pipes are rubber orings that are terrible because they don’t last long and usually is recommended to replace them eventually.
You will be surprised how much help these little things can do to a bike that’s got a vacuum loss due to caked up old rings or it’s struggling to start.
Intake Pipe O-RING (Inlet Boot Seals) x2 – GV125 GT125 RX125 GV250 GT250 Hyosung
Please becareful with intake pipes, the 2014-2019 bikes have intake pipes that are much much soft and prone to splits than the old school bricks of the 2003 bikes (trusted inlets, they are thicker and rubber is better quality). General consensus is that new shape (2014-2019) bikes were a little rushed than the old school 2003-2010 era bikes with grey engines.
It may seems like a little more maintenance is needed on factory new shape bikes but overall they are still wonderful when everything runs right 🙂
I hope i have made some sense but report back as you go along , i will keep an eye on this topic , you got this 🙂
// Meditation doesn't mean you have to sit still....
