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View Full Version : 400ex carb in 300, need jetting


enduro400rider
10-17-2006, 03:07 PM
i know some of you will tell me to search but i have spent the last 2 hours getting my motor together and put back in the bike and now i need to go to work so i am limited on search time........

i have a 400ex carb on my 300ex the 400 carb has no choke, i have an UNI filter, and a web cam. its running the stock exhaust for right now. it is in Ohio... not sure the elevation, right now its running very rich (no suprise) and i need a suggestion on jetting for it. thanks for the help
dork
10-17-2006, 07:06 PM
what jets are in the carb now?
10-17-2006, 07:08 PM
im running 148 with mine but it was rich (before my piston)

dont know about how mine will run now that i have a high comp piston

i would guess 140 main 38 pilot
enduro400rider
10-17-2006, 08:48 PM
Originally posted by dork
what jets are in the carb now?

as far as i know its stock jetting, i bought it used. 148 seems lean i thought i read people were using around a 160, i searched for a couple minuates but couldnt really find anything deffinant
10-17-2006, 09:49 PM
Originally posted by enduro400rider
as far as i know its stock jetting, i bought it used. 148 seems lean i thought i read people were using around a 160, i searched for a couple minuates but couldnt really find anything deffinant

160 is way to rich for a 300

i had 125 main in my 250x carb
cals400ex
10-17-2006, 10:12 PM
the kid i sold my stock 400ex carb too said the stock jetting worked good in his bike. he tried smaller jetting initially but he said it was lean. so i dont' really know. i would do a plug chop at idle, 1/2 throttle and full throttle to get in the ball park.
dork
10-17-2006, 10:57 PM
what throttle position is it running rich at? also, the stock exhaust will definitely make it want a smaller main.
bwamos
10-18-2006, 08:18 AM
Originally posted by enduro400rider
as far as i know its stock jetting, i bought it used. 148 seems lean i thought i read people were using around a 160, i searched for a couple minuates but couldnt really find anything deffinant

I'm running a 160 main w/ 42 pilot, 2.5 turns out.

But I'm on a 330 w/ cam, port polish, oversized valves etc..

160's waay too big for the stock motor.

The 400ex carb may be too large for the stock exhaust. May not get good velocity.

Start with the 148 that's in there.

That usually works good with the pipe/filter no-lid combos, so you'll probably have to drop down from there.
enduro400rider
10-18-2006, 02:10 PM
alright i just went and picked up new jets today, i got a 140 main and 38 pilot. it had a 175 in it when i took it apart. it didnt have a pilot at all. i didnt know it didnt have a pilot and it ran better on the 140 but once i found it had no pilot i put the 38 in and it ran even better, now it seems to have a flat spot at the bottom but pull decently mid through top, i have the pilot screw all the way in, should i back it out any?
10-18-2006, 02:16 PM
Originally posted by enduro400rider
alright i just went and picked up new jets today, i got a 140 main and 38 pilot. it had a 175 in it when i took it apart. it didnt have a pilot at all. i didnt know it didnt have a pilot and it ran better on the 140 but once i found it had no pilot i put the 38 in and it ran even better, now it seems to have a flat spot at the bottom but pull decently mid through top, i have the pilot screw all the way in, should i back it out any?

so is the 140 good? or is it still rich?


i need to buy some more jets for mine all i have is Dyno jets 148-170

also where did you buy your jets from?
enduro400rider
10-18-2006, 02:52 PM
Originally posted by Kickstarts_Suck
so is the 140 good? or is it still rich?


i need to buy some more jets for mine all i have is Dyno jets 148-170

also where did you buy your jets from?

seems to be good, i still have to fine tune it, it doesnt really seem to be rich i think i just need to adjust the pilot jet, seems to be lean on the bottom. i got my jets from my dealer, they set me back about 5 bucks a peice
enduro400rider
10-18-2006, 03:22 PM
i just went out and tried adjusting the jetting again, i backed the pilot screw out 1.5 turns, its running rich (i think) it hesitates at low RPM, i pulled the plug and it was black, i pulled the plug before i adjusted the pilot screw and it was a tan color, im guessing i was closer the first time and mabe that 140 main is still to rich? i might back it down to a 136 or 138 tommarow and see what happens
10-18-2006, 03:43 PM
Originally posted by enduro400rider
i just went out and tried adjusting the jetting again, i backed the pilot screw out 1.5 turns, its running rich (i think) it hesitates at low RPM, i pulled the plug and it was black, i pulled the plug before i adjusted the pilot screw and it was a tan color, im guessing i was closer the first time and mabe that 140 main is still to rich? i might back it down to a 136 or 138 tommarow and see what happens

ok thanks because i need to buy some jets too i guess ill get 135,140

lowest i have now is 148 that came with my 400ex carb and dyno jet kit