I have a 2001 400ex. It is basically stock other than a WB CDI, K&N & Outerwears, Custom airbox lid (mostly entire center cutout), Modified stock exhaust & Dynojet jet kit. Been experiencing some issues with getting the jetting right. After modifying the exhaust the 170 main jet in the DJ kit runs lean. I have decide to trash the DJ kit and revert back to oem jets & needle. What would you guys recommend based on the mods listed? I already have the 42 pilot in and is working perfect. So basically I need to know an approximate main jet, needle position & fuel mixture screw adjustment. Thanks in advance guys.

 

Switched back to oem jets but kept the dynojet needle due to a stripped screw. I went with the 165 main as a starting point with 2.5 turns out. Warmed it up and put a new DPR8Z plug in and ran at WOT for 10-15 seconds, pulled the plug and it is white no brown at all.

 

it looks like mayby you should have stepped up to a larger size main jet if your DJ kit was giveing you what i assume lean problems. i would try a oem main jet higher than 170. my rule of thumb for carb jetting like that is its ok to be a little richer (darker brown) with in reason than it is to be border line lean.

 

I guess what baffles me is that the mods I have are not that great and I figured I would be running rich. I just dont get why I would need such a large jet.

 

well, when ever you do these modifications to the intake and exhaust of any motor, you are allowing it to breathe better. that is why you need to modify the carb jets to keep that air/fuel ratio in tact, so as not to run hot and destroy things. dont be afraid to step up on the main jet, it will not hurt anything. i dont recommend this on the present day engines, but back in my motorcycle raceing days in the 60's i use to sometimes drill out the main and pilot jets. sometimes it worked out and sometimes it didnt, but it never hurt anything to try. (buy new jets then for under a buck)

 

hey u got the same mods as me, except i dont run an airbox lid at all, and i have stock exhaust.

On the instructions that came with the dynonjet kit, it tells u how to set up your jetting for your elevation, with either using stock exhaust or aftermarket exhaust, take a look at it your instructions, if u dont have them anymore ask me and ill get u the info, i suggest to try this, but of course it still may not run right not all exhaust are made the same, good luck.

 

hey rick its me just got on here and thought that i would be no help to your prob .but i wanted to say hi and FIX IT BEFORE SUNDAY and mine too lol .im still thinking as to what jets to get ... 155,158 or both .

 

No offense but I did read the instructions obviously. But you may not of read my first post as I stated I am getting rid of the Dynojet kit and have decided to go back to the keihin (OEM) jets. You might as well consider my air box lid mod as off with the cutout I made. So I will try to make this a more simple question.

Based on me having a White Brothers CDI, A custom air box lid (see Picture), K&N with Outerwears and modifying the stock exhaust (see picture), What would you guys recommend as a good starting point for getting this dialed in. If I remember my elevation was around 600ft. In the picture below you will see the Air box lid that I drafted up and am using currently as well as the modification to the stock exhaust pipe. Also is a pic of the plug (NGK DPR8Z) at a 3rd gear WOT pass with a 155k main, 42k pilot, stock needle on 2nd from bottom and fuel mixture screw 2.5 turns out. I will be switching back to the DPR7Z plug after getting this tuned as my heat range on the ground strap is perfect with this plug plus not to mention there is a night and day difference. Hopefully I have made this a bit more clearer. Also as a reference if the plug pic does not show up good the base ring is mostly black with some brownish continuing down to just over the first thread. The porcelain is still a dull white with no specks or build up and the ground strap is gray with no build ups.

Mod and Plug Pics

 

My bad dude, nice drawings man, hows the exaust sound with the mod u did to it, and let me guess your stripped screw is down in the throttle valve on the part that connects to the arm, if it is i had one there too, when i first took it appart to put in the dynojet needle, the one srew stripped out the first time i turned on it cheap screw, i took it down to the local ATV shop and they got it out for, said i was lucky it ever came out, I bought some good screws so i wont have that prob again.

 

No prob. The exhaust is not much louder than stock but does sound much better, much more throaty so to speak. It gave me a noticeable performance on bottom to mid. 4th gear would pull up just by nailing the throttle. It was the same screw you mention but i used a dremel and cutoff disk to make a slot for a flat tip screwdriver and it popped right out. Good thing when I bought the DJ kit I also bought like 5 sets of stainless screws for the whole carb.