performance muffler
 

hi everyone if I put on a performance muffler and its popping when I let off the gas should I readjust the air/fuel mix or is it something else I used the performance muffler off a parts scooter I just got both are gy6 150cc I is the only upgraded so far thanks everybody for your input

Sounds like you are running a little lean, so some larger main jets may help.

per muffer
 

thanks I need to great a new carb the one that came on the scooter is sealed I got the plug out so I could adjust the air/fuel mix but on the bottedem it just has like steds so I'll just get a new one with a different sizeing jet kit and go from there I still need to upgrade the c d I/coil what would be a good size jet to start with when I get the new carb or just try it out first thanks for all the help

Wow. Sounds like you can't get it apart at all. The computer controlled motorcycles have it made because they can just change a chip to compensate for intake and exhaust mods. The chips can be pricey, though.

Just thought of something that could help temporarily. Restrict your intake air a bit.
-Since high flow air intakes can cause a lean condition, seems that a more restrictive air intake could cause a richer mixture. I realize that restricting the intake kind of defeats the purpose of performance exhaust, but it may be worth it to prevent engine damage from a lean condition.
-Experiment by putting some electrical tape (or something that matches the color of your intake) over the intake opening to see if it helps. Start by adding just a bit of tape and add more, a little bit at the time to see if it helps the popping. Junkyard engineering works sometimes.
If the intake restriction doesn't help, it probably indicates that a lean mixture is not the problem.

spray paint a wiffle ball black and put it in the exhaust or something similar

Backfire
 

Most likely cause of the backfire is that the head pipe or the "slip on" pipe is not sealed. When throttle is closed any leaks allow air to enter the pipe, this creates hot lean exhaust along with lots of backfire. Check the pipe front to rear for good clamping and especially the gasket at the head.

per muffler
 

Maddog uyour problle right the head pip just slips into the muffler I toke it off a scoot I bought last rear but could,t get a title so I keep it for parts I'm new to all this I thought it was a per muffler so I put it on it looks like the ones on amazon what if I get it welded the parts scooter only had 900 mi on it by the way motor runs real good and its for sale thanks guys:shrug: