Hyosung GT125R Carb Carburetor problem
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Hello, I bought a gt 125r. and i have some problems
after starting the engine. the rpm goes up to 6k when i set the idle to 1700rpm and give it gas. Turnover is increasing, but falling very slowly
I set the carburetor. on the feeler gauge. it is very evenly arranged
when I connect the set Carburetor. only the front cylinder works. the rear cylinder starts to kick in at 4k rpm
when I disconnect the spark plugs in the front cylinder.and set the center cylinder to start and have idle at 1700rpm.
and connect the spark plug in the front cylinder, the speed jumps to 7k rpm and stays like that
check the air tightness of the intake and there are no air leaks
and I have one more question if I can replace the original Carburetor . on Carburetor PD26JS -
Do not worry , keep the original carbs, nothing on the market beats genuine mikunis. And they have more than enough power for a 500cc those carbs even a small GS Suzuki 250E bike.
Right, let’s narrow this down bit by bit.
How good is the sparking ? what happens if you change front and rear coils ?
Fitted fresh CR8E plugs ? (it is to rule out plug faults too)
Keep HT caps in mind , the oem HT caps are always sketchy.And what jets (pilots and mains are inside the carb?)
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jets pilots and mains are inside the carb is original I think
I didn’t check the spark in the first cylinder. will check it tomorrow
and the HT caps will check tomorrow too. but i’m ordering a new one anyway.
it is strange that when it fires on the front cylinder, the revs increase to 6k. when i set link idle. is 1700 rpm. and I add gas, it takes a long time for revs to increase. when the rpm grow slowly fall down when I stop adding gas . -
Hello . I checked spark plugs. they all give the same spark. it’s not the spark’s fault.for the rear cylinder to start working. must choke to max . and I have a question if when we give choke . throttle is closed or very slightly open ? . and unfortunately . when I can make it work on both cylinders. I twist
air mixture screw . nothing happens . -
Hello . I checked spark plugs. they all give the same spark. it’s not the spark’s fault.for the rear cylinder to start working. must choke to max . and I have a question if when we give choke . throttle is closed or very slightly open ? . and unfortunately . when I can make it work on both cylinders. I twist air mixture screw . nothing happens .
Now it makes sense , it sounds you definitely need the carbs removed
- Have them ultrasonic cleaned first (as it has many holes inside)
- Check to make sure pilots are size 15 each
- Set mixture to 2.5 full turns out, (Never ever touch this screw again, no matter the issues), this is close to Korea set up of 2.5 front / 2.75 rear
- Main Jets should be 87.5 front and 90 rear if bike is completely stock or 90 front or 92.5 if it has any exhaust mods (any)
- Set the slide need to rich mode
- Make sure float height is 7mm.
If in doubt, replace floats and also replace the gold float seats and float needle on the bike from a rebuild kit. It will thank you for it.
For carb jetting , slide mode , see tutorials in the “TutoriaL” section of this forum 🙂
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ok understands everything. I have a few more questions. this is my first motorbike.
I have a hard time getting into neutral. it very rarely happens
Is it normal for the fuel cap to suck in?
front valve cover . does it have a lot of pressure inside? when I unscrewed one screw. it took a long time for the air to come out . Is it normal ?
The lid gasket was glued on with silicone. today I cleaned it and gave new gaskets and screws -
ok understands everything. I have a few more questions. this is my first motorbike. I have a hard time getting into neutral. it very rarely happens Is it normal for the fuel cap to suck in? front valve cover . does it have a lot of pressure inside? when I unscrewed one screw. it took a long time for the air to come out . Is it normal ? The lid gasket was glued on with silicone. today I cleaned it and gave new gaskets and screws
- Use good quality oil like “Motul 7100” , it is very recommended. Change oil filter too.
- Check “foot rest” for wonky / loose linkages , as it makes it hard to shift
- This sounds crazy but check your rear wheel chain slack, chain too loose or tight will make it hard to shift also.
Valve Cover is sealed to keep compression inside the engine , yes 🙂 but no air must leak. Also check no oil is leaking.
Fuel Cap “hisses” sound like a snake because of pressure during heavy usage of bike or summer heat , it is the fuel cap that will make sure the bike doesn’t “lock up” fuel system or cause running problems. We call this “Fuel Cap is venting to atmosphere” , thats why sometimes a little smeal of fuel from the cap is normal , just make sure the cap looks okay and not damaged.
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oh my God . I don’t think anyone cares about this bike. and it will be hard for me to restore it . I also noticed that the egr is removed . I just changed the oil to motul 10w40 filter too . I changed the plugs to iridium ones. I don’t know if it’s good or bad .
Tomorrow I’m going to drain the rest of the fuel from the tank and fill it with new clean fuel -
I think they fixed it. it already has normal rpm at idle. reacts quickly. to add gas
cause it didn’t work on the rear cylinder . there was a Air Mixture Pilot Screw . its end was broken. blocked the fuel or air canal . i was able to get out. needles from the other side .I installed two new screws and it works fine now .
which does not change the fact that . that the crankcase ventilation was clogged. After removing the screw, nothing is hissing anymore.fuel tank only. sucks in. I don’t know if it’s normal or not .pasting links to videos
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There is a ventilation/breather-hose connected on the underside of the tank, check if it also has been blocked…
Old and grumpy,(?), have fairly wide engine & tuning experience, "restoring/resto-mod" on cars & mc, worked as electronic tech. (retired).
GT125R - sold. New (used): 2012-GT250R-efi (sold)+ 2017-GV-125C (sold) - got my old 2018-GT-125R back... 🙂
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