Hyo flat spot fixed

[Pajjy]

I really should have done this a long time ago.

CDI unit mod, flatspot removal

Smooth accel throughout the rev's, until around 5-6k where it would just lose power, in most cases i would gain more accel out of changing up a gear and going into lower revs under the flatspot than just accelerating through it. Since i bought the bike i have just adjusted my riding style to avoid the flatspot as much as possible. Although every now and then it would sneak up on me and i would be reminded of how unpleasant and seemingly unnecessary it was.

In my particular case i just unplugged the brown plug, from the small black box under the seat sitting on top of the battery (CDI unit), On my bike there are 2 wires running through the brown plug.

One wire, from what i assume, is the cause for the flat spot in acceleration, and from what ive read it was hyosungs cheap solution to pass EU emission standards. I also read that its due to the test being done at 5-6k rpm, and simply cutting the power cuts the emissions. All this means for me is a stupid flat spot in my midrange.

From my research i assume that the other wire is for the kickstand cut out switch, as my kickstand switch was already removed by prev owner it did not cause any starting problems. (other gt250 owners, upon removing the whole plug, and hence both wires, complained of starting problems.)

More info here

http://korider.com/index.php?topic=16600.0

for other hyo owners interested.

Just wanted to post up as i wished i had found more info on this when i first got the bike.

Others have cut the blue/green wire, or pulled it out of the plug itself, as i was skeptical due to lack of solid info on the web i opted to just pull out the plug and try and start to bike, it started, ran fine. Like i said before im pretty sure the other wire (in my case) is the kickstand cut off switch.

In the end it took me about 2 minutes of tinkering for a huge difference in performance. My test ride down the street turned into a 40 minute ride because i was so damn happy with the difference
My bike is a 2005 GT250

Mike

[Ridges]

I have done this for both bikes I've had now. I simply cut the green and blue wire going into the CDI. I had the flat spot at around 5500 revs, but now it's completely gone like yours.

[devolved]

I thought this was only an EFI problem. Mine only has a flat spot when its cold, generally it runs fine. Might have to have a look now and see if its been cut.

Thanks for the heads up.

[agrid]

Its not some wire that adjusts timing is it? I remember some KTMs had a mystery brown wire that you plugged in if caught in the boonies and can only buy shit fuel.

[Pajjy]

Not 100% sure what the wire does, i assume it adjusts (ruins) the timing around 5500rpm as its only a simple carby engine.

Devolved, i actually forgot sometimes that my bike did this, until a mate had a good ride on it and came back to me saying "man that flat spot is so annoying".

But i have been on my second "much longer than necessary" ride today, big difference, well worth a look!

[devolved]

My blue wire was already cut, but the "Korider" site says blue & green, so instead of cutting another wire, I just pulled the plug out (which only had the blue & green wires anyway). Took it for a jaunt around the block, not sure if its made any difference. Will give it a couple of days.

[Ridges]

There's 7 different CDI set-ups apparently...so it could be a different colour. The way I feel the flat spot is if you slowly accelerate till about 5.5k and hover; you should feel the bike start to 'die', twist the throttle and it surges through it. Maybe your sidestand switch has been cut?

[devolved]

No, I checked the side-stand switch and it works as normal. Will check lights & bits before I leave this morning.

*Rode to work this morning, and once warmed up it seemed to be running smoother. Checked all lights and kick-stand shut off and all works as normal. So the plug will remain detached.

Thanks for the link to the korider topic - that was perfect.

[Pajjy]

Glad to help

[devolved]

NOTE:
Went to leave work tonight and my bike would not start. It was like it was getting no fuel, starter motor was turning over, but no fire.

I decided to see if I put the cable back in the CDI if it would fire up - and it did. So now it shall remain plugged. I don't understand why it would work for 2 days and then refuse to start, probably some sort of sensor. Anyway, anyone thinking of trying this mod, beware of this little glitch if you pull the brown/green cabled plug out.