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North UK

Well explained , now i fully get the picture, so if you want a tequila shot answers , ill shoot em below:

  • Fuel Pump wanning (happens, carb cleaner sorts it when you take it apart CAREFULLY) or as pre-caution, replace with a new one if you want us to get it.
  • Fuel Filter Clogging or not flowing fast enough¬† (if its OEM)
  • Fuel Float Level¬† low¬† (repeated in service manual too)¬† (check floats are on a good height, as fuel goes low, then the jets won’t reach , due to pump & tap not replacing the fuel fast enough = high revs . high speed , more demand)
  • Carb Slides wanning.
  • Carb Slide needle may be on the lean setting¬† (sent 1x needle for free, just incase one of yours is bent too)
  • TANK TAP , wanning = Common.


Since its naked, after a ride , check carefully that both cylinder heads are hot or get an oven thermometer against each head,  mark their temps,  then check plug colours.

Plug checks will be a very good way to tell me how your “spark” “air” and “fuel” system is doing¬† , not a full picture but enough hints to show me.

Side view of the plug threads  (heat check)
Top down view of plugs  (to see the white cones inthe middle)

I could advise further after your next comments.

Normally , when a hyosung that is all OEM and negelected¬† (either by garage or last keeper) , the carby 125 ones at least ,¬† they usually spend their lives in the city with a max of 40mph runs ,¬† then owners use crap service parts on them to keep em going,¬† but never touch the carbs , or do engine clearances¬† (valve clearances do eventually get too tight , being a hot engine doesnt help)¬† ¬†, never changing air filter….

Fast forward , the next owner buys it 100 miles away from his house.

He decides to pay the neglectful seller, goes on A1 even to ride home 100 miles,  40 miles are okay but last 60miles involve dual carriage ways of 70mph , he breaks down as soon as he goes from 40mph to 70mph and races it for 2 mins straight, the bike stops sparking  , but all the owner can do is coast it to the side of road , electrics are still on!

What happened?

Negelected Fuel System!!!   (& some times heat damage to coils,  stator & the reg rec = also common)

He starts the bike again after letting it sit for 6mins ….


The cranking & cranking was sending fuel back to the carbs so that the floats can raise and the jets can finally reach the fuel level needed to start.

Now he must ride 40mph max so that the “wanning” fuel system (all of it) can still keep “trickling” down more fuel to maitain fuel level to get him home


His electrics are kinda calm under 5-7k revs …..but the bike rides better at 8-10k revs¬† (catch 22 for him!)¬† ¬†UNLESS he is in fifth gear above 60mph, then lower revs is fine but his fuel system already forced him off road if he goes beyond 40mph on dual carriage ways.

He is now forced to ride away from big roads until then.

Seen it.  Witnessed it myself.

// Meditation doesn't mean you have to sit still....