plug up with what? are you running a filter to catch the crap or are you talking about just gumming up?

Always with a filter, it just gum's up, I run with a glass see thru filter so I am able to see whats going on.

What carb do you have? 

Is it getting plugged in the needle & seat or the jets?

What are you doing now to correct for the problem?

what is considered... sitting long periods of time

so after reading this thread i remembered that i was having some issues myself labor day weekend...so i decided to pull the carb..found the inside of the bowls all whited out [condensation] primary float didnt want to move! and power valves were el shot! so threw some new power valves in it and a cleaned up the bowls and did some good ol fashioned cleaning! also one of the vacuum line plugs was loose and cracked...also accelerator pumps had alot of sand in them...i guess im just saying give the carb a good once over! i try to start my dirtbike and boat up once a week to get fresh fuel in there and not something that is going to sit!