Having problems getting a DVX jetted right

[northwest Texas]

Hi guys, I just subscribed after having been an off and on viewer of the forums.

Anyway, my brother in law bought a DVX 400 several months ago (it was a demo) and after a couple of hours of riding it will foul the plug I guess (it doesn't look too bad) because once you replace it, the engine will go back to running right. The symptoms are it doesn't run quite as crisp I believe and then it just won't start. New plug and she's fine.

Anyway, he decided to install a full Yoshi exhaust. Initially it wouldn't start at all and finally it got to the point where it would. I think we changed the plug but I don't remember for sure. We couldn't get it to run more than a minute and that was it. It would take a new plug to fire back up after several times of that.

So anyway, he's got it running now but it's still not right. It hesistates and stumbles I believe although I've only heard him riding it once since he's got it running. It seems like most of the problem begins near half throttle and gets worse.

Here's the particulars. To begin with, we checked all of the jets and such in the very beginning. All were stock #'s, 130 main, I forget the other #'s but they all corresponded to stock sizes.

He has installed a Dyno jet kit. A DJ needle has replaced the stock. I believe the clip is in the next to top position making the needle low in the carb. I think he has a DJ main jet #120 although he has had the stock #130 in there initially when he put the pipe on. We kept going down in size (main jet) until we could get it to run which explains the small size.

I don't know if it's getting too much fuel or what, it acts like that is the issue. My weak spot is the carbs.

As for the other particulars, the elevation ranges around the 3-4,000 foot range.

I can't think of anything else right now and I figured the more I talked, it might eliminate some questions

[dodgepower]

Did he take the snorkel off to get more air?

[northwest Texas]

It runs better with the airbox lid off. You can definately tell a difference.

[Colby@C&DRacing]

I would recomend removing the airbox lid and jetting it to run this way. Install a 25 or 27.5 pilot jet, turn the fuel screw out to 2.5 or 3 turns from seated and install the dj main jet and needle in the recommended setting for your elevations and mods. It would also be a good idea to check the valve clearances to make sure they are in spec.

[foxman_23]

texas: i have a 2003 kfx 400 that i also installed a full yoshi exhaust on . i have since put the athena 435 kit on and a few ohter mods but with the stock bore i was running a 150 main and 25 pilot. also it would not run or even start at times unless i removed the airbox lid. if the problem is still there try the next hotter plug
e.g.cr8e got to a cr7e

[DVXchic]

I own a dvx and had a DG full system on it. I put a 155 main jet in it and it ran like a top, but now iam am running a new full system and it won't run properly, it shoots fireworks out the pipe. The only thing i can tell you is to call yosh and ask for the proper jetting specs, they will tell you what they are for that pipe.

Good luck

[northwest Texas]

We got it running late last night and he took it for a quick spin after dark and it seemed to be good. We took both his and mine out today and rode them and we have his nearly dialed in.

He claims there's still a tiny hesitation in there somewhere but I haven't felt it but I'm used to my 400EX.

Anyways, what we ended up doing was drilling the plug out to get to the pilot screw and adjusting it. It was turned 1.5 turns out so we turned it to 3.5 per specs and installed the 128 DJ main jet.

The exhaust has turned a little blue instead of the gold so we must be a little rich, right?

All I know is his will smoke my 400EX now in a straight line. I am impressed.

Just wanted to let you all know what we did and where we stand. Thanks for all the help, it was appreciated.

[dodgepower]

Was fun finding that right air screw cap huh? I drilled the wrong thing before finding the right one.

[northwest Texas]

not too bad. We didn't have a drill stop so I was turning the drill bit slow, fortunately the brass was soft and cut easily, but the bit kept going and going and going but it wasn't a big deal. He's had the carb pulled out so many times he's gotten pretty good at it.