125-200cc Help with Mikuni Carb Issue

Hi All

I have recently bought a 2012 WR125 with OEM 144cc kit.

I just replaced the pilot jet on the carb, went from the standard 50 down to 40.

Now when the fuel tap is turned on the carb is constantly leaking fuel from the float bowl overflow hose.

Does anybody have any suggestions on what this could be and how to fix it please? Carb is the standard Mikuni TMX 38.

I am really hoping it's not an issue with the float bowl. I tried to be as careful as I could and not touch anything in there, and replaced the pilot jet through the drain plug hole. But I did kind of rotate the carb through 90 degrees to access the drain plug.

Thanks!

I would check the float to make sure it's height is correct and it's able to move up and down properly.

Sounds like something stuck in the needle of the float.

Take apart again, and pull pin / float, and the small squarish needle with a round pointed tip (Under opposite end of float). I have a feeling that little needle is not seating all the way, and allowing fuel to gravity drain out of the bike.

Not a hard job on these little bikes luckily! You'll be quicker the second time around!

Thanks for the replies guys.

Pulled the pin/float and the needle, re-assembled and no more leaks!

Double check your float level. Should be about 8mm.

Yup!

A lot of them come high from the factory.....you can tell if you get crappy gas mileage even if the bike runs good.

I lowered my floats and went from 18 to 21 mpg in tight woods.

I'm going to check mine, but where do you measure the height from any pictures showing this?

Search "float" and it will come up. My float was between 5-6mm would that cause bad mpg?

Absolutely. You should be able to just about lean bike over to where the footpeg almost touchs ground without the fuel spewing out overflow. Otherwise it is pumping out fuel on every bump. Mine was bogging on bumps when you roll throttle off and back on where it wouldn't do that on level ground. It was not only spilling fuel on ground but flooding the engine when you momentarily shut throttle off.

That is exactly what mine was doing at this past race. I set it up on my home track (which is nowhere near as rough as the recent race course), during the race as soon as I would roll on throttle, it would burble/sputter and then pick up. I know it was running a little rich, but I had to ride with throttle applied the entire time to keep if from sputtering in turns.

Ive the samee problem it was bogging down as soon as i opened the throttle. So if i lean the bike over so that the footrest is nearly touching the floor i should not havve any fuel coming out....will try this and see if the float as above quoted is 5-6mm.

Float should be 7.5 - 8 mm.

Wheelied the bike out of my garage with the fuel on it leaked fuel so this would explain the terrible mpg. The float height has now been adjusted and only leaks when the carby is at a 45 degree angle.

Be carefull with that wheelie out of the garage move when you get the 165 mounted. It will have you picking cement out of your neather parts and replacing the the rear fender quickly. Get used to the instant response and bottom hit first. JMO

Lol typo error should have been 'wheeled'. Saying that i may try a wheelie out of my garage ill have the wife ready with the camera..lol

Fitted a 480 main my slide has a number 5, but the pilot i cant see any markings. That said the bike idled okay as a 125. What exhaust muffler you using walt?

I use the FMF Turbine Core II. If you need a spark arrestor it is pretty hard to beat performance wise. Some guys think it muffles the tiddler scream that we all like to hear. You kind of lose that with the 165 anyway. Much deeper bark. If you don't need the sparky then the power core is good and the stocker isn't bad either.