Now that the jet kit is installed...

[Vx2]

So I now have the Yosh full system, K&N filter, and Dynojet installed. Throttle response and accelleration have both improved. But when I am sliding through or coming out of turns the engine starts to sputter, almost like it's going to die. This happens even at high rpms during a power slide.

What could be wrong??

Thanks.

[buster024]

What jet size did you use? Is your airbox lid off? How many turns on the air/fuel mixture screw? What notch is the needle at?

[Vx2]

The dealer installed a 170 jet. The air box lid is still on. I did not plan on altering the lid. I don't know about the turns on the screw since I didn't install it.

Thanks.

[buster024]

I'm not an expert, but I fiddled with my carb enough that I can re-jet my bike in about 15 minutes. It sounds to me like it may be to lean...??? Try dropping down to a 165, second notch, 2-1/2 turns. I run a 155 main jet, and I've got the same bike, with the same mods you do. I pulled the quiet core out of my Yoshi, and I don't run with my airbox lid on, so I had to drop down quite a bit. If you've never done it, just ask, or check out the following link. It's pretty simple stuff if you take your time.

http://www.exriders.com/vbb/showthread.php?s=&threadid=221872

[underpowered]

Originally posted by buster024
I'm not an expert, but I fiddled with my carb enough that I can re-jet my bike in about 15 minutes. It sounds to me like it may be to lean...??? Try dropping down to a 165, second notch, 2-1/2 turns. I run a 155 main jet, and I've got the same bike, with the same mods you do. I pulled the quiet core out of my Yoshi, and I don't run with my airbox lid on, so I had to drop down quite a bit. If you've never done it, just ask, or check out the following link. It's pretty simple stuff if you take your time.

http://www.exriders.com/vbb/showthread.php?s=&threadid=221872

your goin the wrong way there buddy. installing a smaller jet is goin leaner, a larger jet size is goin richer. without teh airbox lid and quite core you should be richening up you jetting, not leaning out. ever don a plug check on your bike? i would do that and see what ti looks like.

[Vx2]

I am leaving the air box lid and quiet core on. Is there any adjustment that I can make without changing the jet again to stop the sputtering??

[buster024]

you're totally right bro'!! Sorry for the bunk info all!! However, now I'm confused. My bike wouldn't stay running at all once I pulled my quiet core out of my exhaust, so I think it's too lean. I dropped from a dynojet 165 to a 155 and it runs way better. What am I missing?
Sorry to partially hijack the post!!

[Vx2]

So is there anything that I can do to stop the sputtering without having to change the jet again?

[400exstud]

Originally posted by Vx2
So is there anything that I can do to stop the sputtering without having to change the jet again?

Keep in mind that jetting is related to throttle position, not RPMs. Both are two different animals. You can be going up a hill at wide open throttle but only be doing around 4000 RPMs. Understand?

Not to your question. There is nothing that you can do to stop the high THROTTLE sputter as this is the main jet's responsibility. The only external air/fuel option that you have is the air/fuel screw found on the bottom of the float bowl. This is completely useless in you situation because this only is good for idle - 1/4 throttle.

From what you have told me, your bikes simptoms are that of a rich condition. Try to take down the main jet and this should stop the sputtering.

[Vx2]

So I should have the 170 replaced with a 165 or 160 and this should solve the problem?

[F-16Guy]

You are almost certainly WAY rich. I have a 87mm 11:1 piston, cam, pipe, K&N filter, and a vented airbox, and I'm only running a 165 Dyno Jet main (which is still a little rich). For a 400ex with no internal engine mods, there is no way that you should be running a 170 main. You have the kit still, right? Just swap the main out; it's very easy. Use the "Stage 1" jetting instructions that come with the kit. "Stage 2" is for a heavily modified engine, and it won't give you more power unless your engine can utilize the extra fuel. Turn your gas off and let your quad run until it runs the carb out of fuel. Next, remove the float bowl drain (hex shaped plug at the bottom of the float bowl). Now, if you get down and look into the float bowl with a flashlight, you'll be able to see the brass jet with a flatblade screwdriver slot in it. To remove it, I like to use a flatblade bit in a 1/4" socket, since a screwdriver is hard to get in there with. Break it loose with a ratchet, and then use your fingers to turn the socket/bit to remove it. I would drop down to the high 140's or low 150's depending on what's in your kit, but I believe "Stage 1" calls for a 148 or something close to that. Install the new main jet like you took it out. If you can't get it started with your fingertips, you could probably attach it to the bit with a dab of grease or a piece of tape. Run it down finger-tight, and then torque it LIGHTLY. Install the plug, turn the gas on, and fire it up! It took longer to write this than it will to change your jet.

[buster024]

My bike wouldn't stay running at all once I pulled my quiet core out of my exhaust, so I think it's too lean. I dropped from a dynojet 165 to a 155 and it runs way better.

I obviously must have been to rich, not to lean. So to compare, I'm at a dyno 155, and I still think it's a bit rich. I'm going to drop to a 150 before I ride the next time. It's strange to me though still, that when I pulled my core out, I had to lean up my jet.....hmmmmmm:huh ---

How 'bout this.......could it be due to my air/fuel mixture being to rich? Since that screw has to do with the idle or at least the first 1/4 throttle, if that was to rich, would it sputter and die at idle speed? Would leaning out the main have affected that at all?

[Vx2]

So, would removing the airbox lid or installing a power lid from K&N also solve the sputtering problem?

Thanks.

[400exstud]

Removing the lid would get you closER to where you want to be. It still may be off by a few sizes but it will be better than it was.

[ugotbit]

I am going through the same thing now. Take the lid off and try it. You are mostlikely too rich. If it helps you need to go smaller on the jet. I have my needle on the 3rd grove, 3.5 turns on the mix screw and a 155. It runs just like you are discribing with the lid on, with it off its ok...

[F-16Guy]

Another thing that might be throwing you guys off is that DJ jets run bigger than Kehin. If you have the same size (same number) of each jet, the DJ will run richer. You may have to go down to a 146 or 148 to get the jetting right. That may sound lean, but trust me, it's richer than the stock 148 kehin. Keep going down a size at a time until you don't feel any improvement at full throttle, and then go back to the next size up. That will get you really close on the main. Then you can play with the needle clip, fuel screw, and pilot to get the midrange and off-idle dialed in.