1968 Rupp Mini bike won't idle or rev


Im trying to get this mini bike going for me and my son to ride around

As you can see in the video it will start but no amount of throttle input makes it rev up. It also won't idle on its own.

In the video I am running the original carb, but tried a new ebay Chinese carb. That seems to run worse as it will not idle at all. It will start but then dies even with throttle input.

Here is what I have checked:
  • No amount of adjustment on the idle or high idle circuit makes any change.
  • The governor lever is tight and turning the governor rod.
  • Also, it is not a throttle cable issues as I can turn the throttle blade on the carb and it still won't rev up.
  • I checked the valves and they are opening and closing properly.
  • I take the plug out and it shows lean condition.
  • I have new spark plugs, great spark, good fuel flow to the carb and the float is not stuck.

Any ideas?
Check - the fuel flow from the tank; if that's good, check the float level in the carb.
I confirmed the fuel flow this morning.

The float in the old carb was fine yesterday, today it stuck and fuel started pouring out of the intake. I have now switched back to the new carb.

I also removed the head and confirmed I have no stuck valves. I did this because it seems to be backfiring thorough the intake, and running rich as fuel is spitting out of the intake and the plug is black.

Really at a loss with this one?
Sounds like you need a good carb cleaning....check your Float needle it may be swelled and not seating....then as Markus stated check the timing...as a wise man once told me, it may have good spark but is it sparking at the correct time?