I know jetting has been discussed throughout this forum... but I was a little confused when I started the jetting process. My stock main jet says its a "148" but when I read the jetting information on the dynojet instructions it says I should be using one smaller than that?

I think I have the 155 dynojet in there right now and it runs great, but the plug looks like it is running lean (grey/almost white). I have an HMF slip on pipe w/ UNI filter without any airbox mods so what one should I run? I dont want to run hot, but there is no backfiring or glowing of my headers. It feels like the bike is running completely fine. I will take a picture of the new plug once I run it again tonight and post it just to make sure I am not reading it wrong.

Any help would be great!! thanks guys in advance!

 

Dynojet numbers dont line up with kehin jet sizes, The stock jets are rated at diameter, and have chamfers at the hole, where dynos are flat , which prevents a direct comparison
For instance, a stock 148 jet is(move decimal point over 2 places) 1.48mm diameter.


Width------Kehein # -- DynoJets # -- Mikuni #

0,0540---- 140--------- 130--------- 121,9
0,0550---- 142,5------- 132--------- 123,8
0,0560---- 145--------- 134--------- 125,6
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
0,0710---- 182,5------- 164--------- 153,8
0,0720---- 185--------- 166--------- 155,6
0,0730---- 187,5------- 168--------- 157,5
0,0740---- 190--------- 170--------- 159,4
0,0750---- 192,5------- 172--------- 161,3
0,0760---- 195--------- 174--------- 163,1
0,0770---- 197,5------- 176--------- 165,0
0,0780---- 200--------- 178--------- 166,9
0,0790---- 202,5------- 180--------- 168,8
0,0800---- 205--------- 182--------- 170,6
0,0810---- 207,5------- 184--------- 172,5
0,0820---- 210--------- 186--------- 174,4
0,0830---- 212,5------- 188--------- 176,3
0,0840---- 215--------- 190--------- 178,1
0,0850---- 217,5------- 192--------- 180,0
0,0860---- 220--------- 194--------- 181,9

A good guide for do it yourself jetting, with troubleshooting guide for lean and rich is here.
http://www.motorcyclecruiser.c...arburetion/index.html

welcome to the forums

 

Lid on airbox??

 

Thank you hondabuster... very good information. I did not know the stock jets were not in comparison with dynojets for that matter. I will be posting here later after I get down and dirty with my bike.

Yes Koopa, I have the lid on the airbox. UNI filter is all but that isnt much difference than the stock filter. If anyone has a 400ex with my same setup let me know what jet you are running so I can test it first. I will try the 146 (what the instructions say for the dynojets) first and go from there. Thanks again! Ill be back on later tonight.

 

I'd follow the dynojet instruction also. In my experience they have always been pretty good.

FYI, to properly read the plug cut the threads off the plug and look at the shaft behind them.

 

Hey guys... status update on the jetting. This is kinda odd to me, but the instructions with my setup that I listed above told me to run the 146 main jet... I didnt even try it. I had the dynojet "150" in there already and the plug was reading grey/white. So I figured why not bump the main jet up again!? So I put in the 155 and did a run up and down the road getting on the throttle the same way I tested the 150 and pulled the plug and got no more grey/white but got this instead:

http://www.geocities.com/troy824/honda_400ex/plug.jpg

http://www.geocities.com/troy824/honda_400ex/plug1.jpg

http://www.geocities.com/troy824/honda_400ex/plug2.jpg


I know these may not help, but what can I do to richen it up? Or does this plug look good? I have always been told that the plug should be tan and not just "dry". My brother said it smelled "lean" when we pulled the plug. Dont know how lean smells but it didnt smell like gas on the plug. The quad runs great (the same as the 150) I think and has no sputtering/bogging/backfiring/etc. Am I just worrying about nothing here or should I wonder why I am running the 155 over the 146 like the instructions say? I got the clip on the 3rd section of the needle which is where it should be. It looks "rich" and black deep in the porcelean from the last picture.

 

The dynojet guys have always been pretty dang close in my experiences. You can look for instructions for reading plugs again, you have to cut the threads off the point behind the thread is what you read. The top point that you took pictures of is not the correct way to read a plug. Put the dj 146 in and run it. If it don't back fire you are probably fine and the 155 is rich. Rich will make the bike sluggish on the top end. Lean will backfire. Rich is better than lean so if your not comfortable with a 146 bump to next level.

 

If you click on the camera icon to the left, under my name, youll see some spark plugs and where to read them.
I gave up reading spark plugs a long time ago. The additives and oxygenators in modern gasoline, really mask the reading. And unless you do a plug chop exactly as they say, the results dont mean a thing.
Just go by the drivibilty symptoms...it its lean, youll know it, that article lists what to watch for.

 

Thanks guys... Ill take that into consideration. Once I try the 146 I will post the results and let you know how it went and how the quad ran. Ill cut the plug threads off at the base as well to see how that reads. Thanks again guys, and Ill be posting here soon to keep you updated!

 

I think I need to go up a pilot jet size from the stock 38 to a 40 or 42... anyways, anyone know a good place to find these? I seem to be having troubles searching the net. I am also getting rid of the dynojets and going to the kehein jets to keep it easy. Now I gotta buy the stock needle since that has been lost as well...errrg.