Running Hot....too lean?

[jrm03]

i finally got my fmf powercore 4 slip on installed and sounds great. i also installed my dynojet kit and the change was immediate. i am afraid to hit the trail because after it idles for awhile and a short trip up the road it seems the motor is running hotter than before. Could i have the mixture too lean or is there something im overlooking. any suggestions on how to fix it. thanks for all the help 2002 400EX

[krt400ex]

sounds like it's too lean. does it pop when you let off the throttle? does it feel sluggish off the bottom(like it's starving for fuel)? is the spark plug a nice tan/brown color? if the plug's a tan/brown color you should be o.k. if the bike is exhibiting any of the other things I described, then your running too lean. it might just be that you revving it more than usual because it sounds cool. i know thats what i did alot with my 300ex when i got the aftermarket pipe. and it was running hotter but the jetting was correct. i finally relized it was because i was riding the bike harder. if every thing is normal you can get a set of air scoops from UM Racing for around $80. they should help it run significantly cooler.

[JPhonda]

also it should run hotter when its just sitting there or going for little trips down a road or something because you arent getting a lot of air to the motor to cool it. When you are in the trail you are going faster so there is going to be more air to cool it off. All you have to do is just check your spark plug. If its brown then your all set. If the tip of the plug is white then you are to lean.

[jrm03]

when i let off of the throttle it does pop and bang a bit. also on the bottom of first and second it does stumble a bit then it comes out of it and pulls hard into the redline. Im no mechanic so i do not know a lot about it. I have not checked the plug(not really accessible without removing things). Can i check the plug while its cool or do i have to check it hot. I changed the pilot jet to a 42 and that didn't help the starting any.

[4fifty]

first off. you dont have to remove anything at all to get to the plug. get the tool in the tool pouch or get a thinwall socket. car sparkplug sockets are too wide. someone has that tool. pull of the sparkplug wire/boot whatever you like to call it and take it out. it doesnt matter if its warm or hot. i like to put in a fresh plug every time i try a different thing while jetting. that way you see the results and they are looking different because of the burn on it from before. if it is popping and backfiring you are probably lean. on sparkplugs, if it looks black=rich. if it is white=lean. you are better off rich than lean. you like too get a tan burn on the plug. if you have too...take it til it gets too much fuel and boggs when you ride. check the plug. its black then back the jet down a few sizes. if its rich. that means a lot of fuel. if its lean it gets too much air. rich runs crappy. lean messes up engines. so get it black if you gotta. then back down some. it will seem hot if you are sitting or going slow. its air cooled. so give it some. also most aftermarket headers give off more heat.

04 sparks yfz
02 sparks, roll design 440ex FOR SALE
02 sparks 400ex wife
88 lrd 250R sold
01 lrd 416 ex just sold

[cals400ex]

how far out is your fuel screw?

[jrm03]

i went three and a half turns from seated like the dynojet kit said

[cals400ex]

is that with a 42 pilot jet?

[jrm03]

that is correct. Setting...... 2nd groove on needle. currently 146 main 42 Pilot and 3.5turns on air fuel mixture screw

[cals400ex]

i dont' know much about the needle and mainjets, because youare using dynojets. i would only go around 2.25 turns out with the fuel screw myself, with that pilot jet in anyways. also, you could try the 3rd clip position from the top of the needle.

[400exrider707]

Originally posted by cals400ex
i dont' know much about the needle and mainjets, because youare using dynojets. i would only go around 2.25 turns out with the fuel screw myself, with that pilot jet in anyways. also, you could try the 3rd clip position from the top of the needle.

Isn't the third clip stock? I would go down to the fourth. Or second from the bottom.

Also heres the conversion from dyno to kehein so you can tell the difference or about where you should be...
hole-----Kehein #--- DynoJet #---Mikuni #
0,0570----147,5------136--------127,5
0,0580----150--------138--------129,4
0,0590----152,5----- 140------- 131,3
0,0600----155------- 142--------133,1
0,0610----157,5----- 144------- 135,0
0,0620--- 160------- 146------- 136,9
0,0630--- 162,5----- 148------- 138,8
0,0640--- 165------- 150------- 140,6
0,0650--- 167,5----- 152------- 142,5
0,0660----170------- 154------- 144,4
0,0670--- 172,5------156------ 146,3
0,0680--- 175------- 158------- 148,1
0,0690--- 177,5----- 160------- 150,0
0,0700--- 180------- 162------- 151,9

[cals400ex]

yes, the 3rd clip position is stock. i know in the later years honda put a needle in the 400ex that isn't even adjustable. i am not sure if they started that in 05?? but i was assuming he was using a dynojet needle?? the dynojet needle actually has 6 clip positions if i remember correctly. the problem with just comparing mainjet to mainjet is that the needles can play a role in which mainjet is needed. a needle with a little leaner tip may require a larger mainjet than a needle with a smaller tip. maybe this chart takes the needles into consideration but i highly doubt it. however, knowing these comparisons would still be very helpful because it is going to be impossible to get the bike running right at stoich without a sniffer.


Originally posted by 400exrider707
Isn't the third clip stock? I would go down to the fourth. Or second from the bottom.

Also heres the conversion from dyno to kehein so you can tell the difference or about where you should be...
hole-----Kehein #--- DynoJet #---Mikuni #
0,0570----147,5------136--------127,5
0,0580----150--------138--------129,4
0,0590----152,5----- 140------- 131,3
0,0600----155------- 142--------133,1
0,0610----157,5----- 144------- 135,0
0,0620--- 160------- 146------- 136,9
0,0630--- 162,5----- 148------- 138,8
0,0640--- 165------- 150------- 140,6
0,0650--- 167,5----- 152------- 142,5
0,0660----170------- 154------- 144,4
0,0670--- 172,5------156------ 146,3
0,0680--- 175------- 158------- 148,1
0,0690--- 177,5----- 160------- 150,0
0,0700--- 180------- 162------- 151,9