Get the $185.00 in used bills before answering this!
Seriously, you are not going to get this ped fixed on the forum unless you work on defining the symptoms better and not getting caught up in a particular theory without some good reason.
Lets try to get the original problem in perspective first.
Any 50cc ped, even with US restrictions will do about 25 mph on level ground with no wind, even if you weigh 300 lbs! You do not need modifications to make this happen, you just need to make the ped run correctly.
To run correctly, you have to get an adequate supply of a reasonably correct gas/air mixture into the crankcase, transfer it to the combustion chamber, compress it and fire it at the correct time, then exhaust the spent gasses.
Your ped only does 5mph, so at least one of these things is not happening correctly.
You say you disassembled the cylinder so I am assuming this is ok. Do you know if this motor has reed valves and if so, are they good?
Try to describe how the ped runs. Does it idle ok? As you accellerate, does it seem to pull ok up to 5 mph then seem to be gasping for fuel? Do the revs go way up without the ped going faster or do they seem about right for the speed?
Assuming the engine is not over reving:
When running at maximum speed, if you apply some choke, what happens? Do you speed up, slow down or no change?
You say you "played with" the timing. Did this make any difference at all to the way the engine ran. If so, what?
Will the engine rev up quickly to a good speed with the rear wheel off the ground?
Have you tried running without the muffler? What happened?
Have you tried running without the air cleaner and box? What happened?
Try to give answers as specifically as you can. Something like "When I start to apply choke at 5mph, the ped speeds up to 10 mph but if I apply more, I slow down again" or "As I approach 5mph, the engine seems to misfire."
Give us some good questions, I bet we can give you some good answers.