My KLX-300 has been in storage for several months. It starts OK, but when I give the throttle a twist, it stutters or bogs down before revving up...
The carburetor has three transition ports in front of the throttle plate. They are not adjustable, and not usually included on jetting graphs, but if they were, you would notice that just past idle, the fuel air ratio is almost entirely dependent on these ports, and can therefore cause the bike to stutter or stall if totally plugged. All these ports are fed from the same source. Since they are too small and too difficult to access directly, you must clean them with pressure applied to the source. And if one is plugged, the others can release enough of the cleaning pressure to prevent the clogged one from being cleared. The carburetor also has an idle fuel port and idle air inlet port. That's alot of holes to cover while forcing cleaning fluid into one port and out the other, but with one more hand on your left arm and two more fingers on your right, you can do it... :))
Transition fuel ports (3) and Idle fuel port Note idle fuel adjustment screw protruding from idle fuel port Click to Zoom...
Idle/transition air inlet port (left) leads to the idle jet, to the idle fuel screw and port and to the three transition ports.
NOTE => The slide diaphragm is seldom a problem when the bike has been stored for a long time, but crud can congeal around the float valve seat. So before you disassemble everything, connect a piece of clear tubing to the bottom of your carb and run it up the side to check if your fuel level is OK...
Buy some carb cleaner in a spray can with an applicator tube.
Or use WD-40 as your pressurized cleaning source.
Put on your safety glasses.
Fit a small hose or piece of rubber to put the spray tube applicator through.
Remove the idle jet, and insert the hose into the hole where it was.
Cover five of the holes with your "extra" fingers, and spray the crud away!
NOTE => Plug the idle/transition air inlet while cleaning the others. During reassembly, while trying to get the boot over the carb, dirt can easily be scraped off the boot and onto the inside edge of the intake of the carb, where it can enter the idle/transition air inlet jet. So always backflush the idle/transition air inlet jet from the idle/transition fuel jet location. Otherwise dirt sitting in the air inlet jet could be forced further into the carburetor and into the three little transition ports.
When you are sure the uncovered opening is clear, repeat for the other ports.
Clean the other passages in your carb, including the inlet for the float valve
Remove the main jet and spray out that passage, too.