2001 yz426f- NEED HELP with carb.. extremely confused

5 replies to this topic
  • CalebVio

Posted May 18, 2015 - 03:00 PM


hello.. I have a 2001 yz426f and i need help.

the bike pops hard on deccel, will not start without a "prime" (turn of throttle once) and backfires when trying to start.

both the hot start and cold start do not make a difference starting. does not idle smooth, and does not rev very smooth in neutral.. pops and backfires.

The bike runs good when its moving though! no bogging, but no backfires when decelling, just popping. 

jets are all stock im pretty sure. Valves are in spec and I have a 2003 yz exh cam in.

screw 1 1/2 turns out

main jet- 162

pilot- stock (42?)

starter jet- stock

riding at sea level to 600ft 

5-30 degrees Celsius (around 20 right now at roughly 50-70% humid)


Ive had a kx125, 230f, and a 150f and none had gas mileage this bad.. i kinda expected it but holy.. and the bike gets really hot.  

I need help knowing what i should change on the bike.. i dont know if its lean or rich, and the fuel screw really makes no difference.



I know that the forum probably has a thread already but really cant find any info that i can use.. PLEASE HELP! :)

Edited by CalebVio, May 18, 2015 - 03:01 PM.

  • defilmcrew

Posted May 18, 2015 - 05:08 PM


How long has the bike been sitting? And are you sure you dont have any air leaks. There is a ton of 426 jetting threads and stock should be 162 42 pilot. It sounds like the carb needs a cleaning first make sure there is no junk built up in it. Do not split the center gasket unless its damaged. Spray carb cleaner when bike is running around carb and intake side to see about air leaks.

  • Slow and Jerky

Posted May 19, 2015 - 03:44 AM


Definitely  sounds like a plugged idle jet, you need to pull the carb and clean it as well as the passage in carb body. Be sure to pull the idle screw out with the spring and the tiny little washer and o-ring. Also I never use carb cleaner on anything rubber since it will ruin the rubber parts, use brake cleaner instead.If you can't see day light through the jets and can't get a fairly steady stream of brake cleaner to blow through the hole then it is not clean enough. I have used small sewing needles to clear the holet when hard deposits form inside the jet, but you have to be very careful not to hog out the hole. 

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  • grayracer513

Posted May 19, 2015 - 06:19 AM




Also check the condition of the vacuum release plate on the slide to be sure it is not cracked or missing a corner, and that it is installed right side up ("square" edge down).


Let the seal between the slide plate and the slide dry for a few hours before reassembling.  The gas will make it swell.

  • Baldwin

Posted May 19, 2015 - 07:55 AM


I would recpmmend you buy a new pilot jet in stock size. They're a few bucks and it's most likely the solution to your lean condition at idle and when letting off the gas.

If it's not the pilot jet then you're going to have to go on a bit of a goose chase to find the reason it's running lean.

  • mitchbob

Posted May 23, 2015 - 09:11 AM


Had another bike do that was and intake leak, I used starting fluid, sprayed around the carb when you hit the leak the bike will increase in rpm

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