Why does my bike sputter

[nickaloadien]

66cc kit with NT carb everything is checked for air leaks there shouldn’t be any unless i’m somehow missing something.

My question is why does my bike sputter like hell when I let off the throttle?

it has great power and all that but no matter what speed, if I let off the throttle it starts to sputter like it’s choking to death or like i’m going 1km/hr in first gear in a manual car..

what’s up with this?

 

[DAMIEN1307]

if I let off the throttle it starts to sputter like it’s choking to death

Is it possible that what your really saying is it is 4 stroking as soon as you let off the throttle, but would also do the same thing when not accelerating but trying to stay at a steady speed as well.

If so, does it immedately accelerate, when you reapply the throttle and not bog down any???

You probably need nothing more than to relocate the C clip on the needle valve, but before I recommend to you in which groove to put it into, I would first need to know what groove is it set into already and what is your elevation above sea level as this makes a difference, also what mix ratio of gasoline to oil are you running???

If you are still breaking in the motor, which should be done for the first two tanks full, you should start out at 25:1...If it is already broken in it should be 32:1.

 

[nickaloadien]

I run 40:1. It accelerates just fine when I reapply throttle. there’s 5 slots on my needle and it’s set to the one above the middle. I’m at 0 elevation. I will try raising the needle to the very top to lean it out and also use WD-40 spray around for air leaks.

 

[Sidewinder Jerry]

I run 40:1. It accelerates just fine when I reapply throttle. there’s 5 slots on my needle and it’s set to the one above the middle. I’m at 0 elevation. I will try raising the needle to the very top to lean it out and also use WD-40 spray around for air leaks.

You can try dish detergent and water mist spray then look for bubbles. There's also the smoke method where you lightly blow smoke in the conection areas then look for rapid movement in the smoke.

 

[DAMIEN1307]

I run 40:1. It accelerates just fine when I reapply throttle. there’s 5 slots on my needle and it’s set to the one above the middle. I’m at 0 elevation. I will try raising the needle to the very top to lean it out and also use WD-40 spray around for air leaks.

It's your bike not mine, but I will say that on a regular, non-modified China girl, the mix should not be any less than 32:1 for proper lubrication as well as cooling and to also avoid "soft seizures" of the piston and cylinder as well.

If your at sea level or as you say zero elevation, that needle valve C clip should be running just about perfect in the middle position of that needle valve, that is if everything else is totally correct on it including any air leaks either through the head gasket, carburetor, intake or exhaust gaskets, as well as cylinder bottom gaskets.

These kind of leaks happen very often because people do not realise they have to re-torque the head after every single heat and cool down cycle for at least the first 200 miles until everything settles down and seats in, as well as checking the carb stays tight, has the O ring installed in between carb housing and intake manifold, etc. etc.

 

[Deleted member 33388]

Don`t forget to check the crank seals for an air leak also.

 

[GW's Motorized]

Are you pulling in the clutch during deceleration? If not your bike is engine braking which is not good for a 2 stroke engine.

 

[ImpulseRocket]

Sounds to me like it's four stroking when holding steady throttle and not accelerating. Some level of four stroking in that scenario is normal. Excessive 4 stroking that can cause it to feel like it's being choked for air, juddery, and caused the throttle response to be a bit wonky is usually from the fueling being a bit too far off. As @DAMIEN1307 stated, a simple needle adjustment will likely solve most of it assuming there are no other issues. Not likely all of it.