new bike runs bad
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My bike is a 2017 Hyosung GT125 COMET, currently 10.700KM on the clock
My bike has sat outside, under roof, over winter and then it startet to run bad. when this happend i had little to no knowlege to carburetors and such so i turned the air/fuel scews out to 3 1/3 and 3 turns out and the bike ran OK ish, used it like that for a while until i wanted to properly sort out the problem. since then i have: Replaced sparkplugs, checked spark (well over 1cm) cleaned carburetors, jetts, checked float height (my bike was set to 8,5mm but set it to 7mm and made no difference), also checked diaprham all seems good, checked vacum lines all is good, checked fuel lines all good, checked valve clerance its spot on, checked coils and i THINK they are like the way they should be i mean, it has good and strong spark nice and blue. Air filter is also good looks like new.
im starting to think that my carburetors are faulty and im better of getting new carbs. please, ask anything i have run out of ideas.
-Sebastain
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Hello,
Set the mixture to 2.5 turns each pot. Take out the pilot jets and look in the sky with them, if light does not shine thru the pilot jets. This could be a problem and also a sign that carb needs more aggressive cleaning (Yes , sometimes CV carbs not just hyosung, but may need cleaning 2x) unless it has been in a good ultrasonic bath + air compressor afterwards (there many holes inside the carb)Also check fuel filter for any debris coming from the tank.
The fuel should be E5 (it may be called different in Norway) but here in UK , E10 fuel is generally bad for bikes (nothing great about extra ethanol)
Also when bike is running, spray carb cleaner to carb rubber intake pipes and also rubber holes for airbox, if any revs change, you have air leak. Sometimes changing “manifold orings” under the carb pipes helps a lot.
If you can, wait for bike to be 10 minutes hot, then test compression for cylinders.
1. Take out spark plugs (both of them)
2. Compression tester (a good one!) inside cylinder one (front engine)
3. Twist throttle to full throttle.
4. crank the bike for 10 seconds and look at compression numbers and tell us.
5. Repeat this for rear cylinder.Clearances when bike is overnight ice cold (that means let it cool down overnight, then check in the morning) all intake valves will be 0.12mm-0.15mm optimal (0.10-0.20)
All exhaust clearances will be 0.25mm optimal (ish) but range is 0.20 to 0.30 max.
Did you also set the floats when carb was upside down on the table ? to 7mm ?
I would also caution that if there is any doubts about the “fuel valve” that’s under the float, its okay to replace it with some rebuild kit or even just get new floats.The float area can also cause big issues from starting bike to full throttle if its not behaving well.
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Hello Marcel, thanks for comenting.
I have checked the pilot jets and they have a clear hole when looking thru it, i can see light shining in. i have also cleaned the carbs maybe 5 or 6 times now. Fuel filter is fine, fuel comes straight thru. in Norway we realy only have two types of fuel, regular (95) and super (98). regular is just fine it is what everyone uses. I have sprayed start spray on the inntake manifolds and nothing changes, revs stay the same, i have also checked the inntake manifold rubber orings, they look like new.
i have not checked the compression but i realy doubt the compression is bad consedring that the bike ran just fine before winter but i’l probably check compression when it stops raining.
I checked the float height by leaning the carbs so that the floats sits in a resting position and springs back up when pressing it down. it is set to exactly 7mm and not 17mm like the manual says. the fuel valve also looks like new, there is rubber on the tip, nice and clean, no wierd spots or wear marks. event the springy thing on the float valte springs right up like it should.
clearances are checked, they are spot on.
i appreciate your help, but i have allready tried this, i also forgot to mention that the bike has black plugs but i dont understand how that is possible, all the jets are stock, exhaust is stock, air filter, needle clip position is stock…. and the bike still runs rich and stumbles when reving it, it barely revs over 6K.
either way thanks for the support.
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Can you attach pictures of the plugs if you can please ?
Side view ( so we see threads )
Top view ( to see middle colours )Also have you tried a fresh set of CR8E plugs ?
Also , are you able to test your coils for primary and secondary resistance ? (sometimes coil is bad, and HT caps can’t output enough spark power to plugs at high revs)
Also , remove HT caps and measure ohms of HT caps without coils attached to it. (sometimes coil is okay but HT cap is breaking down / stress)
For the Jet needle , have a look at this tutorial to see if it helps
[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250
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If there is any issues posting pictures,
Please try this topic below to test , so i can fix any bugs on the site.Test Topic (Can everyone use this topic to test pictures please)
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