2004 comet 125 loads of problems

Sounds stupid but is there any way at all you can get the bike warmed up for 5 mins hot

remove both plugs out

Put a compression tester in front engine , crank full throttle for 5 seconds.

Do the same for rear engine.

Can you tell us the compression figures.

I feel like it is very important to start there 1st before i would advise anything else for that matter.

Similar issues last week , a client of mine said he needed a new engine which we helped him get despite me cleaning his carb & tuning it twice.  His rear engine had low compression!

I hope it is not your issue but it is usually overlooked , she’s a big girl!

Regards

Start with this item:

Intake Pipe O-RING (Inlet Boot Seals) x2 – GV125 GT125 RX125 GV250 GT250 Hyosung

Clean and inspect your rubber intakes.
Mask the engine holes! (can’t stress it)  then use a good old toothbrush  (not a metal brush!) and some carb cleaner on the brush ,  clean the area on the cylinder heads where the intake pipe sits on.

Then get carb cleaner again (3x cans, yes 3 cans…)  = blow every single hole you can see inside the carb ,  there is loads of them.

Inspect the diaphragms and make sure the needle is at the “Middle Groove (OEM)”  or “1 step DOWN facing the float bowl”  using this guide.

[Tutorial] How to adjust Carb Slide Needle (Tuning) – Hyosung GV & GT 125/250

Get fresh rubber bungs below:

Carburettor Carb Air/Fuel Mixture Rubber Plug (Adjuster Screw Bung) – GV125 GT125 R RC GV250 GT250 Hyosung

You WILL lose one.

Set mixute to 2.5 turns out each and do not touch it ever again unless i advise you to.

Get fresh CR8E plugs and go for a test run.

Keep in mind , if you open a carb , use “JIS” screwdriver , because regular philips drivers WILL round off the bolts and it is hell removing rounded off bolts!

Throw the bolts away and get these:

Stainless Steel Top Diaphragm Cover Carb Bolts Kit – Hyosung GV125 GT125R GT125 GT250 GV250

Stainless Steel Float Bowl Carb Bolts Kit :: Hyosung GV GT 125 250 Carby Models

When fitting your carbs to the bike,   go to halfords and get “matching stainless” bolts for the intake manifolds after putting them new o-rings.

The carb must be on the airbox FIRST , screw tight  (not too tight due to weak rubber holes on airbox)  ===> Then hold the airbox + carb together and SLOW drop down to fit the whole thing in to the intake pipes.

Screw intake pipe clamps tight but not too tight! (These pipes are expensive and super rare now)

Consider checking your fuel pump and fuel tap  = Both of these are at the shop ^ ,   overhaul it all

Consider also:

• Vacuum pipe (at shop)   (tutorial here)
• Fuel Pipe and Large Filter  (Hyosung says in their manual “any rubber hose” that’s 4yrs old (doesn’t matter mileage) rubber rots inside which will lead to eventual clogging of your jets etc..)    (Fuel pipe kit is at the shop)    (tutorial here)

Check your main jets and verify the last owners didn’t put stupid sizes on the carb making it too boggy to run  (tutorial here)

What we have done here is “overhauled” the entire fuel system in time for spring season too.

Now, with that being said:

• Your compression is good! Engine is fine.  (we will deal with the clutch later)
• Find time to do valve clearances   (tight / loose tappets) directly affect how it starts and how it runs. Hyosung says every 4k they must be “checked” to be adjusted or see if they are still in spec.    They are similar to the old suzuki  “cam under bucket” style with shims, so familarise yourself watching youtube old videos of Suzuki bikes having their valves being down, then use the Hyosung Service manual for a proper job done.
• If the fuel system is all new and overhauled.    Your next war will be electrics & air filter    (air vs spark vs fuel)  . you’re doing the fuel parts first.
• Oil = Motul 7100 is the MOST recommended oil for hot twins and i personally would not even dream of using crappy brands like Castrol Power 1 nonsense.
  Silkolene Pro 4
  Silkolene Comp 4
  Motul 7100
  Motul 300v
  These 4^ should be your only options.
  (Oil Change Tutorial here, because previous owners sometimes remove the wrong bolt under the bike and gearbox is gone!)
• As per manual replace filter and o-rings everytime   (see kit here)
• Fuel = E5 only.  Forever.  The carb bikes don’t like E10 and the power is just crap! very wasteful fuel.
• Flush =  “ONLY THIS PRODUCT” <—-  Do not touch redex!  (Put £12 of fuel in tank and then pour the whole bottle inside tank, ride as normal!)

Unrelated but possibly related?
– Choke Cable ?  (kinks or frayed may make the carb not fully close the choke)
– Throttle cable (same reason)

If in doubt get both new cables from the shop, your throttle will be more snappy and smoother on your hands , so you can actually feel what’s going on.

Hope this helps and good luck!  Keep us posted.