Hyosung 250 GT 2003 Comet help

**DoObs** · 5th July 2008, 00:32

Hello Guys

Great forums imo, hoping for some insight on my bike.

Alrighty, my bike is a 2003 model, good condition, but its back firing when i de-accelerate, and if i've already riden it during the day, it will make the popping sound out the exhaust...

So yesterday i took it to my uncles garage, hes a car mechanic, we lifted the tank, and he took the air filter box off. so the carbs were visible.

Now he turns it on, and he has this guage to test the sucktion of the air intake into the carbs its sucking well from the first carb, closest to the front wheel.

Then we did it on the back on, and no sucktion at all. Another thing he tested was if the back spark plug was firing which is was. But now the bike is running, with no air filter on, and he unplugs the back sparkplug plug, bike carries on running, so he plugs it back in, and unplugs the front one, bike stalls and turns off. How does this part work. So now would you guys say that becoz of the above problem so to speak, that there would be less power. The back spark plug is definitely working coz its got that brown tinge to it on the top where it sparks.

Mate here at work says that the first Carb is for lower RPM and the other will kick in at a higher RPM.

So those are those things, Next is:

When im in 3rd gear, i find the powerband dips a bit, would this be to lack of acceleration or is the a fault here. I find i have to like rev it a bit , like de-accelerate and then accelerate again for it to kick in.

Also how do i tune the bike, if its running lean or rich etc.... Bike has new spark plugs air filter oil filter and oil in. Using Unleaded 95. A oil 40.

Um yea i think thats it.

Thanks guys

DoOb's

**King_Rider** · 5th July 2008, 00:47

I cant answer your question about the tuning of the carbs or about the second carb lacking suction as I always had a mechanic do work on the carbs but I suspect the popping is caused by the carbs being tuned too rich. The good news I have for you is the problem with the powerband in third gear. I had this same problem when the bike was low k's but after wearing it in some this problem stopped. You said it is a 2003 model though which is a bit confusing coz you should have worn it in enough by now... How many k's have you clocked up?

**DoObs** · 5th July 2008, 01:05

Its got just over 54000km's, Purchased from Yahama Ekerold, Maritzburg.

I will have to Phone Kawazaki motors, in Umhlanga.

If anyone can shed some light on these things im having a problem with, do post.

**King_Rider** · 5th July 2008, 01:21

Sorry I couldnt help much before but this thread should be much more useful:

http://www.korider.com/forum/modules...ewtopic&t=7970

**Renegade** · 5th July 2008, 01:22

are you sure that the power surge isnt an rpm issue cos mine did it at about 5k rpm, had a flat spot then took off again. as for the carb issues no idea, but maybe its time for a overhaul of them, try [url]www.richardhyosung.com, hes a helpful chap.

**King_Rider** · 5th July 2008, 01:28

This is what they are all saying about your problem on that thread:

"My 07 GT250R had the exact same problem. Pulled the green wire with the blue tracer and the problem went away instantly."

That must be what my mechanic did to make it go away... Ha! I didnt even know about it.

**Gubb** · 6th July 2008, 10:53

Remove the green wire from the CDI unit. It was put there to pass Emission Standards Testing. It retards the timing at a particular point. Yank it out.

**CookMySock** · 6th July 2008, 14:18

Originally Posted by DoObs

Then we did it on the back on, and no sucktion at all. Another thing he tested was if the back spark plug was firing which is was. But now the bike is running, with no air filter on, and he unplugs the back sparkplug plug, bike carries on running, so he plugs it back in, and unplugs the front one, bike stalls and turns off. How does this part work. So now would you guys say that becoz of the above problem so to speak, that there would be less power. The back spark plug is definitely working coz its got that brown tinge to it on the top where it sparks.

It sounds like a fault in inside the engine. I'm thinking something bad has happened with the rear cam.

Have a bike shop look at it.

DB

**DoObs** · 9th July 2008, 02:03

Originally Posted by DangerousBastard

It sounds like a fault in inside the engine. I'm thinking something bad has happened with the rear cam.

Have a bike shop look at it.

DB

Hmm hope its not that.....

l had a idea yesterday, which never even crossed my mind.

The fuel filter, i took it off and what came out the one side was an orange silt type mix with fuel.

Im gonna take it out today see if it back fires, sure it will at first, but maybe this could be it.

Um also how do the carbs work on this bike, mate says that they are classified as First and Second Stage. Where the front carb will work at lower rev's and 2nd stage at higher rev's or are they suppose to work both at exactly the same time.

This could clarify some things about my bike.

Also that CDI wire trick, you say take the green wire out, i did this and my bike didnt wanna start......different wire maybe.

Wait on replys, thanks guys

**CookMySock** · 9th July 2008, 07:59

Originally Posted by DoObs

The fuel filter, i took it off and what came out the one side was an orange silt type mix with fuel.

Im gonna take it out today see if it back fires, sure it will at first, but maybe this could be it.

No that is unrelated, and you might get some junk in the carbs and then you will have two simultaneous faults to deal with - nasty !

Originally Posted by DoObs

Um also how do the carbs work on this bike, mate says that they are classified as First and Second Stage. Where the front carb will work at lower rev's and 2nd stage at higher rev's or are they suppose to work both at exactly the same time.

I THINK they are two seperate carbs - one for each cylinder, so if you have spark, but no vacuum and no firing then you either have a valve problem, a cam problem, or a piston problem.

I MIGHT BE WRONG however, so get it into the shop and get it checked.

DB

**CB ARGH** · 9th July 2008, 08:29

For a five year old bike... That's no good mate. But 50,000KM's is getting very far up there, so you can only expect this sort of problem, from any bike really.

My disgnosis, put a mix of loctite in the carbeurretors before you start the bike.

(DON'T DO THAT HAHA)

**kapiti_nigel** · 3rd May 2011, 18:48

Hi, with regards to the retarded timing on Comet's - I followed the advice on this and other http://korider.com/index.php?topic=376.0 , http://korider.com/index.php?topic=11746.0 threads ..... pulled the wire from the CDI and the bike started performing better through the previously retarded rev range!!! I admit I was very sceptical and, a) expected it not to start, or b) to make no difference....but, it actually worked!

Cheers

PS - my CDI is the following: 32900 H molded in and GT250 M815 printed on in white