hey guys, im in the process of puttin my 400ex back together. I put a wiseco 426 piston kit, HMF sport series slip on, and pretty basic port and polish job, and uni filter. now who out there has done this set up before? its farely common, so i know someone can help me out. I was wondering if anyone out there could tell me how there 426 is jetted, (needle, clip position, jet size.... ) to kinda give me a starting point or somethin i can work with. Thanks

 

jetting really is diffirent for every mechine in veery area, so there is no magical secret to jetting....exept one. you have to be willing to exparament with jets! i would say you may hav to bump up your pilot jet 1/2 turn if you have lag at idol. leave the clip where it is for now, unless you experiance mid-range lag. but you will need to go up a bit on your main jet size. atleast 2-3 sizes up from stock, to start.

but see if you cant get it runing with the stock carb and get a base line of what it needs from there. run it at diffirent throttel speeds in top gear, hit the kill switch, pull in clutch, and read the plug. white=lean, black is too rich, ideal is marshmallow brown!

 

i bored mine to a 416 and nine aint right yet ,i went up two sizes n the pilot jet and got i runnin half way desent with a .155 main jet , what is tthe clip uns r talkin bout ,mine will cut out full throttle so i no mine aint right and its very cold natured now

 

he is talking about the clip position on the needle jet

 

i didnt no u was susposed to do anything other than swap out jets , how do u move it

 

hey thanks for the info fellas. its commin together nicely im just puttin a few necessities in it now waitin for my cylinder to be ready from the shop,(oil filter, new clutch.... stuff like that). How do you like that 416 mudslinger?? could you tell a lot of difference between the 400 and 416?, but as for the clip. just take the top of the carb apart and pull out the needle, theres a couple of clips to undo then jus slide it out. theres gonna be a couple of rings cut all the way around the top of it with a C clamp in one of them. Then jus move it where you want it. (for you probably down to allow more gas intake).

 

HEY GUYS ! damn i completely forgot to mention the most important part of the build..... a hot cams stage 2 cam.... i dont know how that slipped my mind. but i figured you would need that extra info to help me out.. lol. but anyways, i jus tore apart the carb for the first time, and aparantly the previous owner tried to do some modifying himself. my main jet is a 165 ,and pilot is 45. stock is a 38 pilot and a 140 or 148 main. and this is on a stock engine that smoked like a wore out dump truck !!, i guess i know why now. but ok. try to help me out now. thanks !

 

A 155 main is too small for a bored engine. Start with a 160 and go from there.
426exrida, the 165 should be close. When you get it back together try it and see what it does.

 

im runnin a 170 main jet with a je 13:1 piston with a stage 2 hotcam and kibblewhite valves, pipe and so forth. try the 170

 

I would start at the low end and then work from there. Not all engines with the same exact mods can be jetted the same. Too many variables (temp, elevation, humidity) come into play. If you start in the middle you could go either up or down on the jetting making it harder to dial in. Just my .02 since I've done it a million times before.