Flat spot / loss of power when accelerating/decelerating

[GRAViL]

I have a qma139…. another gy6 clone… I have recently upgraded it to 80cc.

 

Prior to the upgrade I had what could only be described as a flat spot when accelerating.. basically as you open the throttle you would hit a point where you would loose power, but by twisting the throttle just a little more it would pick up and be accelerating fine again.

 

After the upgrade the “flat spot” has now become much “wider” in that it now occurs over more of the throttle acceleration range, if that makes sense. But once again if I keep twisting the throttle it will eventually hit a point where the acceleration and power is fine.

 

It does not appear to be effected by the speed you are travelling, if I’m doing 70km/h and move the throttle to a mid point in it’s range of movement the power disappears keep twisting the throttle in the deceleration direction and eventually it picks up again.

 

This is very irritating to say the least…

 

I upgraded the following parts when I did the 80CC upgrade

 

Racing cam

20mm CVK Carb (didn’t work very well… so I used the jets in the existing Carb)

 

That said I have always had the issue… it’s just a lot worse now that I have upgraded.

 

Any help with this issues would be greatly appreciated.. and apologies in advance if there is a post about this already, I did have a look but couldn’t see anything obvious.

 

Regards,

 

GRAViL

 

[Fox]

What color is the spark plug tip?

What air filter are you using? Stock or aftermarket free flow?

[GRAViL]

Hi,

 

Sorry for the late response,

 

 

The spark plug tip was black… I have cleaned it up now, but I’m guessing my mixture is too rich???

 

I’m using the standard air filter that cam with the scooter basically a rectangular box with a piece of foam rubber in it?

 

It feels like at a mid range of revs the scooter starts missing, if I keep the throttle in the position where it is missing once the revs have dropped a bit the engine picks up again until it starts missing again.