Bike doesn’t have power – Hyosung GT125
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Bike Model = : GT125
Hi all!
I’m posting here because I’m a little exhausted to be honest with this bike.
I bought it for little money (200$) non-running and got it to run
Now it’s running and idling but today I went for a ride and it doesn’t have virtually any power, wouldn’t go over 70km/h (40mph more or less) and almost stalling taking of from a stoplight and VERY slow acceleration.
At idle it revs good(?)
Could it be that the spark is weak? Though I don’t smell unburnt gas in the exahust.Tomorrow I’ll try to see if one cylinder is hotter than the other.
What I’ve done:
I’ve gone through 2 sets of spark plugs (NGK CR8E, the first one i’ve lost it the second is on the bike)
Oil and filter
Bigger fuel filter and braided lines
Dissasemble the carburator two or three times to clean it and to un-stuck the accelerator pump which was stuck (now it moves freely but have to test if it’s inyecting in both cilynders)
Re-attached the HT Lead Head (the thing that goes to the plug that is screwd in) to the cable that comes from the coil.
Replaced the regulator, prior one wasn’t charging the battery at all.
New battery.Please I’m begging here, what could it be? Could it be carburator still? Or can it be electrical?
PS: bike has 40.000km on it, in case that’s relevant.
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Okay I’ll do tomorrow as I know someone that can lend me a compression test tool.
If the case where poor compression but the valve clearances where good (as I checked them this morning on the rear cylinder and where in spec (0.1-0.2 (0.2 wouldn’t fit) for Intake and 0.2-0.3 (neither did 0.3) for exhaust), what could it be?
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Compression test done (with a flex tubem didn’t have the metal type near me)
Front Cilynder: 90 PSI (6,4 kg/cm2)
Rear Cilynder: 91 PSI (6,5 kg/cm2)
Check valve clearence and everything checks okay in both cilynders (done it previously to warming up the engine)
What does that mean?
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In your case, the compression is too low, because according to the manual, the minimum service value is 10 kg/cm2.
At what RPM did you check the pressure?
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Did you check the valve clearance?
Lack of compression is one of the symptoms of valve leakage.-
On the rear cilynder I check them cold before doing the compression test, all clear.
0.1 to 0.2 on Intake
0.2 to 0.3 on exhaust
The bike doesn’t burn oil btw, no white smoke
And plugs are a little black but no oil in them, just of the bike going rich by messing with the carb.
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Compression test done (with a flex tubem didn’t have the metal type near me)
Front Cilynder: 90 PSI (6,4 kg/cm2)
Rear Cilynder: 91 PSI (6,5 kg/cm2)
Check valve clearence and everything checks okay in both cilynders (done it previously to warming up the engine)
What does that mean?
Do it 1 more time again, and this time try:
- Pour a little tiny oil inside front and rear intake pipes for the carb, so that oil goes in the cylinders , then see if compression is improved ?
(piston rings or possible slight damage to cylinder walls of the piston cylinder) - Try to get it done with a “metal pole” as it is far more accurate , flexi-hoses have always given me mixed results (sometimes good, sometimes bad) , so i always try to use a metal pole.
- Pour a little tiny oil inside front and rear intake pipes for the carb, so that oil goes in the cylinders , then see if compression is improved ?
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Hi! I did it just like you said and it bumped up to 11 kg/cm2 on both cylinders.
I just have to open them and see inside and look for scratches or the state of the rings right?If it is just the rings, where would I find them? Hyosung doesn’t have anything for this bikes here in Spain.
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Hi! I did it just like you said and it bumped up to 11 kg/cm2 on both cylinders. I just have to open them and see inside and look for scratches or the state of the rings right? If it is just the rings, where would I find them? Hyosung doesn’t have anything for this bikes here in Spain.
It is easier to find used pistons and cylinders on ebay. Some sellers and myself regularly list them there because Hyosung Korea is not making parts for any bike before 2019
So they only make parts for current models now (Gv125-S EFi 2020+ , GV300, GV250DR , GV650PC now)
However , I am still busy studying and researching different rings , until i can find one that will fit GT125 , then i will list them on the shop but for now, our best hope is used parts. Lets hope it is just cylinder or head-gasket leaks.
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Hey, So its just best to find a good used engine from what I gather.
I know that the compression test has to be done at operating temperature, but since I have to buy one second hand and I cant test it at that temperature before because its off the bike.
I can however do a cold compression test because the starter its still attached to the engine, how much compression does it need to have cold just to be shure that the engine its somewhat healthy?
I know they loss compression with temperature but mine had almost the same results cold or hot. So i gather that if at least the compression is good cold, I have 80% chance of being the same or little less when hot?
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Hey, So its just best to find a good used engine from what I gather. I know that the compression test has to be done at operating temperature, but since I have to buy one second hand and I cant test it at that temperature before because its off the bike. I can however do a cold compression test because the starter its still attached to the engine, how much compression does it need to have cold just to be shure that the engine its somewhat healthy? I know they loss compression with temperature but mine had almost the same results cold or hot. So i gather that if at least the compression is good cold, I have 80% chance of being the same or little less when hot?
Usually if it says 125 psi cold , it “could” jump to 150 psi hot (OK to use) or jump 10 extra psi max , depends on engine to engine , hence forth we usually get the final figures after the engine has run for 5-10 mins hot.
Compression tester used should be OK , but just make sure it has a straight metal pole than using flexi hose.
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