[Randall]

Hello,
So I have a 2008 Tank Urban Sporty with a 49cc GY6 139qmb motor that will not start, it cranks, but will not start.

Let me get in to the details... I got it this spring and it didn't start. I wasn't sure how long it had sat around so I put in a new spark plug, new battery and cleaned the carb. Boom, it started.

It had very little power, I had to somewhat push with my feet to get going from a stop sign and it took nearly half of a mile to get up to maybe 25 mph, but you could still comfortably ride it around. I decided to put on an aftermarket exhaust and an unrestricted CDI (not a "racing" CDI). The two upgrades made a marginal difference, but it was now able to go 30 mph. Over time it gradually started to run worse and start with a little more difficulty whether I used the kick start or the electric start (the kick start always seemed to work better).

The engine was running lean so I cleaned the carb again and adjusted the idle mixture while the engine was warm to get the best idle. It would still bog down while accelerating and wouldn't go much past 6000 rpm. Soon it became very difficult to start, it would take 5-6 attempts to finally be able to idle, each attempt would get closer to starting. Once it was able to idle (which was very low) it would die as soon as you even thought about touching the throttle. It felt as if the motor wasn't getting fuel.

I decided to do a slight overhaul and replace the carb with a new one with slightly larger jets and a new electric choke, replace the fuel pump and replace the fuel filter. While I was doing this I replaced the rollers with 6g rollers, replaced the contra spring with a 1500 and replaced the clutch springs with 1000 springs. After this it did not start at all. The engine would crank but would not start even when I used starting fluid.

I have fuel to the carb. I have vacuum. I have spark...

I adjusted the intake and exhaust valves; intake (.002 in), exhaust (.003 in) as these gaps are stated in the manual.

I got yet another new spark plug. (new ignition coil is on the way)...........

.....Same story...... It will not start

I do not believe I would have messed up the timing as I did not remove the cam or the chain, I merely turned the motor via the flywheel to reach "Top-Dead-Center" when doing the valve adjustment. I have done nothing with the stator as I do not want to spend any more money until I have a better idea of which direction to go from here...

I am at a complete loss as to why this motor will not start. I would greatly appreciate any help I can get. I find myself frequently visiting this forum as there are a lot of people here with far more expertise than myself. I apologize for such a long post but I wanted to be as detailed as possible so that someone somewhere might see a glaringly obvious flaw or missed opportunity in my process...

Thank you in advance!