still cutting out
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me and my dad have spent hours working on the bike for it to still be cutting out, befire jt cuts out it splutters and cant get revs up, i have a video of the start up after it’s died it’s very strange, we’ve replaced the fuel tap and lines i don’t know what else it could be apart from spark. here’s the link to my experience https://youtube.com/shorts/lBgN9shK5J0?feature=share
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Hey,
Thanks for sharing the video. My reply will be split in 4 parts. I would do 1 part at a time, so that you can see the mood changes.Part 1
I assume you have or his has found the upjet tutorial on this site ? Use that to make sure the carb has right jets.Once the carb has right jets (especially pilot ones)
Set fuel mixture to 3 full turns out each & leave it there forever (not matter what ever issue comes up in future) , it is the same reply from Korea for users not to touch mixture screws. So once that is set…. Make sure the black bungs hide them , if they get lost, we have loads at the shop. Cheap little things but saves a whole lot of drama in the long run.
Make sure “Slide Needle” is middle groove (OEM) or “Last Groove” towards pointy tip
Tutorial here[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250
Next, can’t stress this part . Get access to air compressor (as per service manual) , remove all jets ==> Blow them hard. “Rattle Can” cleaners don’t always penetrate enough to remove the last microscopic debris.
Or
Have the carb ultrasonic cleaned & THEN air compressor.Believe me, it will be immediately obvious it’s happy with the result.
Fuel Pump = It is rare it fails but can happen, so the carb doesn’t get the juice.
Float Height = It must be 7mm when carb is upside down (floats facing the ceiling of your garage) , not less , not more. Dead on 7mm.
If in doubt, replace the gold parts under the floats = They control how much fuel comes in. Pilot Jets are shorter, so they can’t always reach if fuel level is too low or floats jammed or if the bike always has intake manifolds wet inside ===> Don’t ride it as it will be hydrolocking (floats jammed and fuel is just pouring in to oil) could cause many many many many issues later down the road. So i dare not digress!
Part 2 = Air System.
Check vacuum for leaks on pipes.
Check INTAKE manifolds = “don’t matter how small the leak is” , it will straight cut off. The Hyosung Black 125 Engines are actually more difficult to crank & run if they don’t like the conditions under the hood.
While running ==> Spray carb cleaner at the intake boots or EASY start (Yellow Bradex Can!) , if revs change then you have a leak.Replace INTAKE Manifold “O-RINGS” ,if the pipe is good, but somehow there is a leak, it will be the o-rings under the intake pipes being caked up.
If you have never removed intake pipes from the bike, please take extreme caution for removing the rusty torx bolts used by Korea and replace them with stainless steel of the same length. You don’t want to spend days drilling out a seized bolt lol.
AirBOX = Spray “the airbox” rubbers that swallow the carb mouths. If the revs change, then airbox wasn’t fully sat down properly.
Best installation ? ==> Carbs on the airbox and tighten hard (but gently?) ===> Then drop them on to the intake pipes. This ensures no leaks at airbox rubbers and protects your intake pipes from pressures that will cause splits when trying to fit carbs on to them , then the airbox etc…. New Ones not made anymore. Korea stopped.
Air Fikter = If its beyond 10k miles old or is looking tatty inside and outside, replace it. Let her breath freely.
Part 3 === LECCY SYSTEM
Spark Plugs = Don’t use IX Iridiums (BLUE BOXES), they don’t like em. So only use “Laser Plugs” or Stock CR8E
If a mechanic says use Cr9 or Cr7 = Don’t trust them with your bike.
To cool a Hyosung 125GT more when it overheats ====> Upgraded to a GT250 oil cooler. It loves them coolers. They are way bigger & bolt straight in.Coils = Ask your dad to make sure “primary” & “secondary” resistance of the coils are in spec.
ie. HT wire to Coil Ground = 6,200 ohms & Terminal Pin to coil ground = 0.05 OHM (less than a single Ohm)If in doubt (also common) = Replace HT caps to NGK Caps that have red NGK Factory wires attached and pimp the actually black coils. Common upgrade items after the plugs.
I will assme regulator is 14v idling and 14 at 5k revs = as per Korea. The manufacture says to replace reg if you get 12.x V readings in any revs or even your batter dying out could put a strain on it.
Test stator unit = ALL SPARKING starts from this unit. It is dual Purpose unit.
Pick Up Coil = Inside Stator => 80-120 ohms overnight ice cold.
Charging Element of stator ==> 0.7ohm overnight ice cold.Part 4 (Final war, i hope you don’t end up here!)
– Check compression of the cylinders and tell us the psi each head is making after engine is cold.
DO PSI checks when BOTH plugs are out and FULL throttle.– Valves too tight = Clearances overdue (to be done every 4k as per korea service manual)
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We came to the conclusion we think its the ignition coils, it links to all the symptoms of a failed one e.g. spluttering, bogging, no power Bike is currently at the garage and im waiting for the coils to arrive for me to give to them to fit!
They should arrive soon with your reg rec, minor delay from supply chain but i got you! Reply to the old emails i sent you for updates (not the blue ones , those are just reciepts)
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