Hyosung GT125 - idle issues

[Intruder_Andy]

Hi all just finished rebuilding my bike and having issues getting it running correctly. I've cleaned carbs out and rejetted the mains 9Up one size) as I have cone filters and non standard exhaust. It revs really nicely now but unfortunately it won't idle. It seems to be running very lean as when I add choke it will run (albeit at 3k revs) but turn choke off and it dies. I've tried increasing the mixture by turning out the screws but this had no real noticeable effect.

So do I need to up the size of pilot jet (currently a #15, standard) or are there any other ways to richen the idle circuit.

The idle adjuster screw doesn't help either.

For those who aren't familiar with these bikes, it's a v twin, double carb setup.

Andy

[Quornholio]

Put it back to standard.

Job jobbed.
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[Wull]

Terrible bikes,get rid!
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[Quornholio]

They're not the worst bikes in the world.
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[Rogerborg]

The engines are actually pretty nice. They're already claiming 11kW though, so good job on riding Otherwise Than In Accordance. Might as well have stuck the 250 engine in there.

Based on those symptoms, I can't see any magical answer other than bigger idle jets.

Is there any baffling in the exhaust now? Try sticking your hand over the end of it to give some back-pressure, or literally put a sock over the air filters. That's not a solution, it's just for the lulz and to confirm that you need to sort the fuel/air balance.
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[map]

I seem to recall (certainly on the standard model) the airbox rubbers to the carbs were a bugger to seat correctly and they had a habit of splitting.
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[Dave M]

[Wull]

[Rogerborg]

What specifically went wrong with yours?
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Wull]

[Rogerborg]

If you want to assist folk in making informed decisions, then specifics help.

What carb issues?

What electrics? I've seen a GT125R instrument panel just give up completely, and the horn contacts corrode out.

Rust where? The middle of the swing arm, the exhaust, somewhere else?

Chain? Was it the original, or a replacement?

Sidestand switches are frequently susceptible to problems. My HN is notorious for it, and I've got my Enfield one disconnected. Ewan-and-or-Thingy's BMW switch brought the Long Way Down trip to a temporary halt.

I wouldn't recommend a Hyosung, but I wouldn't totally discount them either.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Quornholio]

Brother in law had one from new, never had any issues up until he sold it.

I've a Hyosung sat in the garage in a state of disassembly. That's because of the carb being gummed after being stood outdoors in all weather.

I'd have a Hyosung over many bikes, TBH. I wouldn't pay the new price for them though, but I'd still own them.
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[pepperami]

I Cant say anything about the 125 versions of the Hyosung twins as I have`nt owned one.
I agree : put it back to standard.

I do however own a Hyosung GT 250r efi and it has been a very good bike.
I keep mine in good order and service it when it is supposed to be serviced + change the oil every 1000 miles (it`s not hard)
I have been all over Great Britain on mine and it has only ever split a link in the chain once.
I might be tempting fate , but it has never let me down apart from the one time.
Would I have another? absolutely
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[Intruder_Andy]

Thanks for all the replies/opinions. I've put standard air box back in now, just trying to sort out a standard exhaust system then hopefully it'll work.

This has been a project bike for me to do up and get used to working on bikes and yes the build quality on these aint great but there are worse bikes about. Would I own another one? Probly not a 125 but maybe a 650.

I have joined the Korider forum but as they seem to be based in far flung parts of the world, replies are few (if any) and take a day or 2to appear, so hence asking on here.

Here's the bike so far.

https://i779.photobucket.com/albums/yy72/photo_w87/Mobile%20Uploads/20140723_073831.jpg

[Dave M]

[Intruder_Andy]

Okay, so quick update. Changed everything topside of the carbs back to standard, original airbox/filter/breather all back on. Mixture at 1 and 1/2 turns out. STILL WONT IDLE!

Only thing non standard is exhaust and main jets. Idle jet is back to original #15.

With choke on it idles at 3-4k when cold.

When warmed up it will idle if choke on (at 3k-4k), turn choke off revs go down then it dies.

I cant put standard exhaust on as don't have one.

So basically I'm back to standard setup aside from exhaust and main jets. Seems like its running way too lean.

Turning idle screw doesn't help as this just opens throttle slightly allowing more air in which kills it even quicker.

Should I up the pilot jets again?

Andy

[Rogerborg]

[Intruder_Andy]