1998/99 kx 125 fuel leaking from carb outlet at bottom

New carbs aren't known for leaking unless you had it open and altered some thing. A float can get stuck if you let it sit without using it. Should put stable in your tank and run it so thestable gets into the carbs.
Check above the carb for a gas leak from the gas hoses and check the gas tank. They may be running down onto the carb and just appears like the carbs leaking

Sounds like a vacuum leak is leaning out the mixture....check the intake between carb and engine for leaks...another source may be tjhe crankcase seals are leaking.

Several things could be wrong. First, the fuel petcock (valve) at the bottom of the gas tank should be turned off when the bike is not being ridden. Also, it is possible the valve may not be fully shutting off the gas. This can allow the carb to overflow and leak gas. A stuck open or punctured float in the carb bowl can cause overflow. The float should be light as a feather and have nothing inside it but air. Is the carb securely mounted?

Check for cracked fuel hose or bad connections at the tank and carb. Is the fuel valve body leaking gas where it mounts to the tank? Heck, with the bike being 36 years old the tank may be leaking at a weld or due to rust through. I wish I could work on your bike. The older bikes are more fun to work on than the newer bikes. Post a reply and let me know what you find.

Hello you have a
1. fuel starvation problem clogged carburetor jets.(clean the carb)
2. Intake leak carb joint/intake manifold.( start your motor get it to idle best you can spray wd40 around the carb joint if the rpms change you have a leak replace the carb joint or gasket/o-ring as needed.
3. crankshaft main seal magneto side leaking or worn main bearing.
check end play on the magneto side remove the cover plate firmly grab the end of the shaft with up an down motion if you can feel it move replace the main bearings and seals.
These are problem that will cause your motor to run lean and hesitate.
Hope this helps you with your problem

Why? What compression reading you got?

Generally less tha 90 it wont run. 140psi would be good. Over 160 would be too much.

If you havent shut the fuel off and the carb leaks then it likely that the crankcase is full of fuel and will give a false compression reading.
The most obvious way to check is to remove the expansion chamber, shake it around and listen for fluid in it. If it has fluid in it- IT GASOLINE- it will burn/ ignite!!!!! Be very careful and dispose of properly
Once you are sure the crankcase isnt full and the carb is right then check compression

sounds like its running too weak ,thats why it runs ok with the choke on, check for air leaks around carb- engine and carb - airbox , use wd 40 and engine note will change when leak found..

the needle and seat on the float may be bad check them

your float is stuck take carburator off and clean wiggle float and it shouldnt leak gas anymore

hi,
to get a good combustion inside the engine, you(engine) needs fuel-air mixture, since it leaks fuel the mixture is too rich on air. Where does the carb leak? maybe it's just the connection that leaks...I mean where the fuel line connects to the carb, If it leaks there it also sucks in extra air instead of fuel, and therefor the engine doesnt run smooth, choke or no choke, that makes no difference. Check that and if it leaks there just change out the fuel line with a new hose.
It could also be the little rubber ring that seals of the carb, If it leaks from the top of the carb...it's the little ring. Take off the top of the carb and check the condition of the ring, if faulty.. replace it with a new one.
Hope this helps....can be pretty dangerous riding around with a leaking carb... Good luck, Gilbert.

2000 rpm and I cleaned bottom of carbs. Someone told running them on full choke would foul out plugs.The bike runs but only when I pull choke all the way out.If it only runs with the choke on it might have a vacuum leak or an air restriction which the choke is counteracting. (very lean fuel mix). To locate a leak you could try spraying CRC around the rubber carb connections and see if the idle speed is affected.,