Agility City 125 runing rough at low speed

[jeeves]

Hi everybody!  Often lurk here, but usually post if a have problem (Mea Culpa  )



I have a 08' Agility City 125 with a Tehnigas 4Scoot exhaust. The scoot has a bit over 45000km.

A few weeks ago the scoot couldn't pull over 50-60kmh.

The problem ended up being a ripped vacuum membrane (about 1cm) that I changed.

I also took out the carb and cleaned it in a ultrasound tub, came out really clean and shiny!
Put everything back in,and just in case changed the fuel filter, spark plug and vacuum tubes because they were little cracks on the connecting points.
It idles fine, and everything above 1/4 throttle it runs great.

The problem is the first 1/4 throttle opening, it surges and you can feel it's struggling until you open the throttle more and then no problem.
There was a bit of backfiring at deceleration, most notable when going downhill. I played a bit with the idle jet and it's better now, but not the way it used to be. The idle jet was dirty when I took it out for cleaning.
The spark plug is not oily, so i presume it's not running rich.
No cracks in the intake, I removed the filter and put a rag on the intake tube and the motor died.
Did a valve adjustment just in case.

The only thing that comes to mind now is that I didn't put the TPS back 100% in the position it used to be (didn't know it even had a TPS before removing it!).
I fiddled with it today, and think it's back at the original position, but it still surges somewhat.

The other thing is because of the aftermarket exhaust it's maybe it's getting enough fuel at low RPM, and maybe I need a bigger slow/pilot jet, but the exhaust has been on for more then a year and the problem only started now. 

Open for any ideas, at this point really don't know what the problem is 

[jeeves]

I think I have found the possible cause for the hesitation.

I was looking on the net for the last few days and found a few good diagrams and explanations on how carbs work. (this is all new to me)
On the original vacuum membrane body there is a really small cut out part on the lower body, close to the neddle that the generic GY6 replacement part I got doesn't have.
It seems that this allows more fuel in at the first 1/4 throttle opening.

Can this be corrected with a bigger pilot jet or do I have to buy the original Kymco part?
The pilot jet in now is 35, waiting for a pilot jet set from ebay and plan on putting a 38.

Picture of the original cut out the generic replacement doesn't have

[jeeves]

Finally got the OEM Kymco vacuum membrane and the scoot work the way it should, no more hesitation at 1/4 throttle [emoji4]

Compared to the generic GY6 part the original has 3 cut outs at the bottom, not 1 as I thought, and the smaller hole at the bottom is in a different position.
Looks like all this makes a noticable difference, so do buy the original.

[Joebug]

thanks for that info...its good to have the problem then the solution to follow....many times on forums, people come looking for help then when they figure it out they never post the resolution.

[jeeves]

One other noticable difference between a OEM Kymco carb and a generic GY6 carb is that the OEM has a TPS.
The TPS is held in place by a metal carrier held in place by one screw. Do not remove the TPS without this carrier because you could have hard time putting it back at the exact place (like me), and a misplaced TPS can give you bad/weird throttle response.

On the generic/aftermarket GY6 carbs the place the TPS is connected is covered by a metal cap. Don't know if it can be removed or if there is a hole on the carb where the TPS carrier can be screwed on.

[PaulF]

Good to hear you sorted out the problem.  Sounds like you learnt a bit along the way as well.