Bike not starting or running
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After having opened up the engine and checking timings etc, we started the bike again and it sounded like it wasn’t getting enough fuel. We adjusted the floats, there now at about 9mm and the bike sounds like it’s getting fuel. However it won’t start unless we block the air by putting a hand over the rear carb (Airbox or tank isn’t on currently) and then we can’t get the bike to start or idle without giving it choke. The rear cylinder seems to be mis-firing despite us having checked the timings and having checked the spark and seen it. We’ve used carb cleaner and re-built them, checked the size of the jets, checked in the engine.
Not sure what to do. New carb floats are on the way. Any help appreciated.
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Have you measured the resistance of the coils (without HT caps attached) both primary and seconday and tell us the figures.
If i think from your numbers the coils are okay, then it would be probably HT caps (if they are stock hyo ones, just replace them with NGK) , the 125s do appreciate the NGK products in this season despite weather , the ngk caps & laser plugs do help the bike start faster and spark even the slightest whiff of fuel coming from the carb
The carb now should be 7mm, i’ve not experienced a hyosung run well on 8 to 9 neither 6mm , it has to be dead on 7mm
If it is 7mm, then check the “float valve” needles actually spring back (has a spring inside) and the tips are super clean & not bent, they control how much fuel comes in the carb in tandem with the floats, some jets can’t reach all that deep in the bowl, so a certain level of fuel should always be present and henceforward the upside down nature of the carbs too (Korea did it this way as its quicker to send fuel to engine) (Downdraft / CV=Constant Velocity , speaking of which , the airbox helps)
You will have to make sure when it runs, there is no air leaks on the manifolds because “O-Rings” sit under them, if they are old or squeezed thin, just replace them. You can test this by spraying all over manifolds to see if revs change.
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