when i first replaced the jets in my carb. i had no exhaust past the h box and air pods instead of a filter box. I replaced the jets from 78/115 to 90/125. things seemed fine until recently the temperature dropped quickly around here and last night i tried to start it with mixed results and alot of backfiring. i added a straight thru exhaust with a couple of 90 degree bends. should i go back to the smaller jets since i have created back pressure? a guy i work with told me i should only go up 1 jet size at a time and i jumped 5 on the low side. any advice would be greatly appreciated because i'm not running like crap in colder weather.