2S People 50 starting issues, BACKFIRES, SMOKES, cuts out when riding. HELP!

[caribeso]

I have two (and a parts one) Kymco People 50 2 Strokes, one a 2001, one a 2008 (w/EPA stuff removed by previous owner). I put them to rest at the end of last year due to frustration getting them running. Now my car died, so I am returning my attention to scoots. The 01 always kicked ass power and speed wise, but started to just cut out randomly for a few seconds, like short little dead spots, and then would go back to running MOST of the time (stranded me a few times...). It started getting worse, so I took it all apart, cleaned the carb real good, then swapped out ignition coils, of course spark plug, took apart the ignition rotor, bought a new non limited CDI, etc etc. Still never stopped pooping out at times. So then I read that a scoot w over 2K kilos or miles, (mine was over) can wear out the top end, so I went and bought a new top end and piston, but got a 70cc kit (which was more work that I thought cuz the skirts on the piston hit the housing, so I had to do quite a lot of grinding).  Well, afterwards this baby REALLY could beat out a Harley at a light, but STILL did the same cutting out after a short while. Now after both have been sitting, they turn over, and i got the 70cc going, but it did the same thing, kept quitting and I'd get stuck somewhere until she would start again.  And at times, I notice gas coming out of the carb throat (pretty sure NOT the float bowl), tho I have read that sometimes that happens. I would think that to be totally unsafe.  Anyway, I have two Kymmies that are not being nice to me. I did replace the fuel filter a few years ago, so didn't take it off this time (one between gas tank and replaced stopcock, not after stopcock). If I take the gas line off the carb, it flows pretty well, and the float bowl is always full. Maybe valve in float bowl is bad? the little spring goes in and out, and point looks clean. Is there something I am forgetting? Please help!! Both are dead. Thanks.

UPDATE: i found a brand new carb, but the casing had a much smaller throttle diameter, so i stole some jets and needles off of it, and the scooter started to run!  but then it went back to the same old thing, and i forgot to mention that when it starts stuttering it also BACKFIRES real loud and starts smoking, pretty stinky.  So those were two things it used to do that i forgot to mention. but at least it starts now...  not sure if the new parts made a difference or not

[stuo]

Where is the back firing happening, at the carb or the muffler? If from the carb you got lean fuel issues, if from the muffler it's spark cutting out, then igniting the gas fumes in the muffler when it comes back on. My hunch is it's an ignition problem.

[caribeso]

it SEEMS to be coming from the muffler, just b/c it is SO loud. but i haven't thought of it coming from carb. could that still be loud? the scoot does stall when this happens, usually coughs 2 or 3 times, then kinda regains itself, and most times goes back to normal.  if it was either of your solutions, then why would it run great for a while, then start doing this? something changing once it gets hot?  thank you.

[big blue]

Yes it could be just an intermittent loss of spark that builds up gas in the muffler when the spark comes back it explodes the charge in the muffler. Have you checked the plug cap? It could have a broken ignition wire that shorts when hot.

[caribeso]

it DOES seem like intermittent spark, which is why i have changed ignition coils (unless they are ALL bad), plugs of course, and even the rotor thing that sends the signal for the spark. i read that these have two sparks for every cycle, one being a dead spark (can't remember the real name), but that seems weird that there would be a second spark, seems like it would tear up plugs faster.  anyway, when you say the the CAP on the plug wire could short out, what would it short out to?  i could understand the wire shorting out to a grounded frame part, but i would think the only thing the cap could short out to would be the plug, unless it jumped all the way to the engine head...

also, i watched a good video of a guy rebuilding a carb on a K50 2T, but his carb had a place for the oil tube to come into the carb, whereas all three of mine have the oil come into the manifold right after the vacuum hose to the petcock, and before the engine, with no stub on the carb for another hose. did they switch that over at some point?  i have 50's from 2001 to 2008... and speaking of petcocks, i have been told that the ones with the filter inside are not good PCs. i would think that the filter should be replaceable, but on Kymco's diagram there isn't one that looks like the paper filter inside it.  they do have a part called People 50 - SCREEN FUEL STRAINER - 16952-KEC8-9000, but that part looks to me like the oil strainer. maybe they just used a stock diagram for the fuel filter, which was an oil strainer, i have seen them do that.  and most peeps don't carry it, as most Taiwan Kymmy parts anymore.  and is there an easy way to test the PC? have one person suck on the vacuum line while the other blows thru the input line?  think my brake bleeder vacuum thingy would also do, but can't find it...

One more thing, in this video, this guy takes out the fuel/air mixture screw, and it has the little washer, but also a little black O ring.  all three of mine have the tiny washer, but no O ring on any of them. chance that all of them were rebuilt before me and three different peeps left out the O ring?  is it an important part?  or maybe his carb is slightly different than all 3 of mine cuz mine have the different oil entry point?

sorry for so much stuff, this stuff has really puzzling me for years.