back pressure

Hey all, I have had this issue for quite some time and have yet to pinpoint the cause. Every few seconds, some air will blow back from the engine into the carbs, quickly hissing out of the boots in the spots circled in the picture, and some even blows back out of the airbox intake. My gut has...

Hey, So basically most of the stuff i've read about shorty mufflers with cb350's is that it won't work because of the back pressure, meaning you need more resistance on the air that is outputting from the pipes. Since stock pipes are longer than shorty's, they don't have this problem. Well I...