1. Fuel cap or fuel tank is not venting properly.
2. Fuel filter clogged.
3. Fuel line pinched or kinked.
4. Float needle and seat sticking.
SOURCE: will only run with full choke and absolutely no throttle.
Carbs gummed up. Need a serious cleaning or a full ruubers replacement/rebuild kit. Gas turns to gummy when left stting in the fuel bowls.
Use a couple of cans of Sea Foam.. best stuff in the world.
SOURCE: rebuilt all four carbs cleaned and replace needle
With Mikuni carbs, the idle circuits affect engine performance up to 3000 rpm under light loads. If the idle circuits are restricted (by fuel gum, rust dust from the tank or dirty fuel, the results will be 1) the engine will run with "choke" on. 2) poor or no throttle response below 3000rpm,3) back firing and missing on the effected cylinder(s). Cure is to blow out the idle circuits and idle screw adjustment jets with several applications of carb cleaner and compressed air. Failing that, strip the carbs.
SOURCE: bike starts right up in choke take it off choke shuts off
when you rejetted, did you also change the idle jets or just the main jets? if you didn't change the idle jets, that would probably help. remember you might also want to raise the float level height just a little bit to compensate for the extra fuel going out.
SOURCE: Replaced throttle and idle cables
It sounds like the slow speed jets or the accelerator pump is clogged up. Did the bike sit for an extended period of time? If so, you need to take the carb off and disassemble it. Then, clean out the jets and the fuel passages. This is not a job for an amateur as there are certain things that will go back together in either of two ways when only one way is correct. But, if you're mechanically inclined and you carefully lay the parts out in the way they came out, you can do this. Use a can of the pressurized carb cleaner to clean any gummy residue out of the carb.
Before you take the carb off the bike. Remove the air filter and with the engine NOT running, crank the throttle open. Watch for the spray of fuel out of the accelerator pump nozzle in the mouth of the carb. If you don't see any fuel squirt into the carb, either there is no fuel in the float bowl or the accelerator pump diaphragm is bad. The accelerator pump is on the bottom of the float bowl.
Good Luck
Steve
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