modified 139qmb sputtering at WOT

[d_cassarino]

ive got a 2012 taotao 139qmb "50cc" scooter. upgrades include 100cc piston kit, 100cc cylinder head ported and polished stock valves, larger cam, 150cc intake with 150cc carb stock jet sizes, high flow air filter, stock header pipe with high flow slip-on. stock variator, rollers, clutch, final drive gears. last year scoot was running fine easily held 55 no problem all the rucks were suprised that my "stupid chinese bike" would fly right by them :scoot: this year my scoot will not go past like 3/4 throttle sometimes 1/2, started checking fuel flow. installed new fuel lines new fuel filter fuel flow is great. cleaned carb and have tried smalller jets adjusting the slide needle, nothing. while up on a bike stand the bike has great throttle response but when held at WOT it sputters and pops. ive checked the spark plug color many times but it seems about where it should be. im lost as to whats wrong here, maybe i should replace the plug and and filter? ive got a long ride coming up this weekend and would like to get my scoot running right beforehand

[Firehawk989]

Is the gas old? If so, drain and put in fresh premium gas and maybe a cap of seafoam.

Are you absolutely sure the carb is clean, like took the jets out and made sure they had nothing blocking them and squirted carb cleaner through all the passages clean?

Replace the plug and clean the air filter because it's easy, and adjust the valves. Also check the operation of your vacuum petcock and look for any vacuum leaks from cracked hoses etc.