Letting today's poor-quality gas sit in the float bowl of your four-stroke is a terrible idea. It results in clogged jets and gummed-up carburetor passageways, causing your motorcycle to run terribly and bog at the worst moments. Gas may start to go bad quicker than you think, sometimes in less than a week.
You can avoid huge headaches by draining the float bowl after every ride or by using fuel stabilizer additives. Unfortunately, for most of us this is way to complicated and unpractical as most of us use our motorcycles for daily commuting. For example one of our motorcycles sat in the garage used for just a few days short of a full month with the fuel switch still on and the result was a completely clogged pilot jet and a clogged accelerator pump passage, Had it just been a pilot jet we could have fixed that easily enough, but since the passage ways in the carburetor were gummed up the fix required the removal of the carburetor form the motorcycle, which isn't something you want to do without the right tools.
Four-strokes are way more susceptible than the old two-strokes to issues related to bad fuel, but no matter what type of motorcycle you have, if it's suffering from a clogged carburetor, we will tell you the best way to get your motorcycle working again. Modern technology is a beautiful thing. If you don't have a service manual, you can always look on the Internet.
In our case a little 3mm Allen bolt at the bottom of the carburetor drains the fuel out of the float bowl. Had we used this the last time we rode the motorcycle we wouldn't be tearing the carburetor apart to clean out all the bad fuel. If you drain the fuel out of your carburetor when you park your motorcycle for longer than a couple weeks, you probably not have problems with a gummed up carburetor.
When you have the carburetor open, pull out the bowl, main jet, pilot jet, float and float valve, placing each on a clean cotton towel on your workbench. Inspect them carefully and begin cleaning using a small set of needle files (the round/tapered kind work great) and carburetor cleaner (careful with the carburetor cleaner it can damage plastic and hurts like hell if you get it into a wound or in your eyes). Our if your pilot jet was clogged up solid!
Remove the fuel screw and try not to shoot the parts across the garage. You'll be cleaning out this passage as well. When cleaning, you want to look for grit or grime that can range from fuzzy and green to gooey and black. A telltale sign of bad fuel is a horrendous stench, so you might want provide good ventilation an open window or door is maybe not enough.
With a Q-tip and some carburetor cleaner get busy on the float valve passage, making sure it is perfect before you move on. Any little bit of grime can have an effect here.
In tight spaces is where the can of carburetor cleaner is your best friend. Spray it through the pilot jet passage and the main jet passage while holding the slide all the way up (you don't want to get carburetor cleaner up around the slide on a four-stroke). While using compressed air also helps blow any debris out, it's probably wise to wear safety glasses. You can go back and forth until you see a clean stream like it looks like new.
Our battle with bad fuel even had the accelerator pump passage clogged up, causing a horrible bog off idle. Using carburetor cleaner and compressed air we eventually got it cleaned out and spraying clean into the bore of the carburetor. Once again, be sure the slide completely open when doing this...
The accelerator pump can get just as gummed up as the pilot let and the passageways in the carburetor, so you have to take it apart and clean it as well. We used compressed air to free the passages first, followed by carburetor cleaner. I guess that the fuel pump of a fuel-injection engine can also be gummed up and cleaned very similar.
Inspect the O-ring, and or gasket of your carburetor if they still look okay. You can buy new O-rings at almost every automotive parts center. Make sure everything is debris-free and clean, reassemble your carburetor and make a metal note to not let bad fuel sit inside of your carburetor so that you don't have to do this again.... But guess we will do it soon enough again and again....