Chinese Bikes/Senke 125/150cc - Lean Sneeze

[m0nsieur_gh0st]

I have a Senke 125cc euro 4 motorcycle that utilises the Alpha-N fueling system.

TPS sensor
Coil Pickup
O2 Sensor
Intake Air Temp Sensor
Engine Temperature Sensor.

All sensors have been replaced. Connectors all clean. Ignition Coil is new. Grounded properly. High Octane fuel. Fuel tank is clean. All service items taken care off.
The problem is I get backfiring into the Intake manifold/Throttle. This usually happens at stead Revs between 2000 - 3000 rpm. Engine doesn't have a problem idling. Doesn't have a stalling issue. The throttle is basic spring operated with a throttle bypass screw.

I've noticed with these Chinese bikes that the timing marks are slightly off. This i've adjusted slightly 1/2 tooth advance. The engine timing was retarded by 1/3 of a tooth.
Initially i thought it was a timing issue with the backfiring happening in the intake. I assumed the Intake valve timing was incorrect by a little bit. However no matter what i do advancing or retarding the timing. I still get the lean sneeze.
I've checked the piston which doesn't look to be in a bad condition. The valves doesn't seem to leak. i've tested this by pooling some fuel on the valves to see if it found its way through the other end. looks fine. The valve springs on inspection look fine.

It seems like the bike is having trouble transitioning from idle to higher RPM. The problem is clearly present between the 2000RPm to the 3000RPM. does anyone have any ideas.
Valve clearances intake 0.10. exhaust 0.10
Engine is a 125cc SOHC.

Thanks.

[WD Forte]

"AlphaN is a method of fueling that uses the angle of the TPS (Alpha) and the RPM of the engine (N) to determine how much fuel should be injected."

but well all knew this didn't we?

If the bike runs fine in all other respects I'd hazard a guess the tps
which is basically a potentiometer (variable resistor), may have some wear or need cleaning.
A squirt of switch cleaner in the tps may help but first i'd put a meter on it and see if the resistance rises and falls in a smooth manner.
Another test is read the voltage from the tps to the ecu and check it rises and falls smoothly as the throttle is used.
Worn/dirty pots tend to jump or have dead zones.
____________________
bikers smell of wee

[m0nsieur_gh0st]

I've replaced the TPS its checked the wiring. connectors all look fine.

What i didn't check when i was connected to the ECU was how smooth the throttle readings were. i'll take a look at that to see if they are erratic when i'm twisting it.

I've noticed the cumbustion chamber is oiley and full of carbon so i'm going to replace the valve seals and piston.

[to v or not to v]