Installing some mods today, jetting advise please!

I currently have a bone stock 13' 400SM, today I'm installing my mods which include:

MRD/SSW - open (no quiet insert)

3x3 mod w/ K&N filter

I have the JD jet kit and extended fuel screw, I live in Milwaukee, the elevation for pretty much my entire riding area is 700ft ASL.

If I could get some advice about the proper jets to use I'd really appreciate it. If I'm missing anything let me know.

Safe settings would be Blue needle 4th clip, 160 MJ jet, 25 pilot with the fuel screw 2.6 turns.  It will run and always start. However if you feel like messing with it, I've found those settings to be really rich in my area (similar in elevation), so you may find the 150 MJ being better, and running the stock 22 pilot gets a better response.


I have a post with my jetting findings in my build up thread here.

Thanks for the reply, I really don't want to be ripping this carb out again, so I'd like to get it right the first time! From what I have been reading, this is what I was planning on doing unless someone comments saying its a bad idea. This is going off the instructions with the jet kit...

Blue needle 3rd clip

Still unsure about the main jet either 155 or 160 but it seems to me that a 160 is kinda big for still being a stock carb/cams/bore x stroke, please correct me if I'm wrong.

As for the fuel screw I was just going to try 2.5 turns and adjust for smooth idle

It is hard for me to find the time to be ripping this carb out so I would like to do it as few times as possible!! Thanks for any and all help!

I found when I was running the stock carb, one clip richer (#4) was better than 3.


There are too many variables, the settings I listed above resulted in a bike that ran fine, just if you are willing to take the time, you can make it better.


If you just want to put it in there and forget it, either the 155 or 160 will be just fine.

Hey Max,


I just re-jetted with open FMF exhaust and 3x3. I have 160 MJ, 25 pilot, screw 2.5 out, blue needle 3rd clip. Pretty much what the JD instructions say. It feels good. 

I would suggest you do use the 25paj. The 155 main may better suit your low altitiude. The 160 will be a tad rich IMHO. Remember when you put in the new Fuel screw you will have to drill out and remove the brass plug first. Use a small 1/16 bit. Remove stock f/s. Install the new one and when you do so screw it all the way in until it just stops. DO NOT OVER TIGHTEN the fine pointy tip of it can break easy. Once at the bottom make note as you turn it out 2 to 2 1/2 turns. The trick is to start at about 2 turns and fine tune the f/s and idle from there. At your altitude the blue needle on the 3rd clip should be good. Note you can change the needle without removing the carb. A bit hard but can be done. When removing the stock needle be very careful because the little plastic holder for the needle inside the slide can break relatively easy. If you do break it you will have to buy a new slide. The JD Jetting instructions are very good. Getting the carb out is fun..not! Remove seat and tank first. Loosen the clamps front and rear. Make note of where the throttle cables are adjusted to. Back off the nuts and remove the cables trying not to bend them up to much. Having the carb clamps loose first helps to turn the carb as needed to do so. When reinstalling and down to getting it back in it is best to get the back of the carb into the air box boot first then clamp and pull it forward and work it into the front one. When pulling the tank there are two lines attached to the carb. Fuel and a vacuum line. Remember to reattach the vacuum line upon reinstall. With the MRDssw you can make your air box hole a little larger than 3 x 3. Use a putty knife heated by a torch to make your cuts nice and clean. If you grind it will throw pieces of crap everywhere. You can also remove the screen in the airbox for even better air flow. Just remember to keep all debris out of the airway path. I used a vacuum cleaner to make sure all was clear prior to reassembly. Its the little details that will make or break the change.

Edited by Jim BurnCycle Abbott

Well the job is done, now it's torrentially raining so its going to have to wait for its first ride until the rain stops. I cut the hole in the air box a bit bigger than 3x3, although the pilot drill for the hole saw I have broke with 2 corners to go so I'm going to have to wait until I go back into work to clean it up and make it pretty. Any tips on taking the screen out? I wasn't aware it came out and it didn't look removable when I was in there.

I ended up using:

Blue needle on 3rd clip

155 main

25 pilot

Fuel screw 2.5 turns

The 160 just seems like too big of a jump from the stock 142.5, that's why I went with the 155. If getting the spark plug out is not a big ordeal ill use that to try and determine if its getting enough, otherwise I have a wideband o2 I can try and Jerry rig in the exhaust for some fine tuning.

The carb took some wiggling to get out, and it went back in very easy after I had the stock exhaust off, with the rear exhaust bolts out, the subframe moves back a good inch, allowing lots of room to get that carb in and out.

I'm pretty sure the adjustment changed on the throttle cables, but after I tightened them down I ran the throttle through the range and it hits both stops so I'm guessing its good?

I'm not a huge fan on how the air cleaner just sits on the fwd surface of the box and is held in buy that shitty wire, the wire is fine I suppose but just sitting on that fwd surface seems like it could leak easily.

That MRD/SSW is a lot louder than I was expecting it seriously barks! I really hate to put the quiet insert in there and lose any gains the pipe gives me in the first place, so I guess I will just have to get used to it. The header pipe is shaped a bit different than the stock pipe, I had a hard time getting the 6mm Allen in to tighten the lower bolt securing the header to the head. I've got it snugged up pretty decent and it doesn't seem to be leaking but I'd like to get a little more out of it so again ill just have to wait until I go back into work Monday to torque that down properly.

Anyway I'll report back with the results once this rain clears which looks like it might be another hour or two, thanks for the replies and comments!

Spark plug is really easy to remove. Just tug hard on the rubber boot that goes over it

So I got out for a nice ride, feels real nice. Power comes on smooth as I roll onto the throttle and WOT it rips. I would say I can tell a difference between stock but just barely, sure does sound faster though! Wheelies pick up easier so I'm happy!

THe QC insert will not harm your gains by much at all. I run one in my MRDssw cuz I want to keep my hearing. I did modd my QC by drilling the holes bigger and more on the end of it.

Turdy. The air box screen is real easy to remove. Just push it in. Then grab it and pull it all out. For the front of the K&N filter I too felt that it did not seal well. Two easy ways to remedy that. One you can coat the front of it with heavy grease or if you want you can go to a hardware store or Home Depot and buy some weather stripping and put a foam seal on the front of it. The problem I see with the K&N and Suzukis wire holder pressing into the back of the filter is that the plastic eventually bends inward from the pressure. Heat like here in Vegas quickens that process. I had some very thick, dense rubber foam that I cut a couple of pieces from and used them to wedge the filter tighter against the front. I also have the K&N precharger screen because I ride in the dirt mostly.

So at first the bike seemed to run just fine. I took it up on the freeway the other day for a few miles and noticed around 70-80mph that I could feel some very faint hesitations, now as the air is getting colder I can feel these same hesitations at most speeds, so I'm thinking its a bit lean??? This is always at mid throttle so am I right to adjust the clip in the needle? I was thinking of going from the 3rd to the 4th.


Also (not that I like to speed, but just an observation) when this bike was bone stock it would hit right around 100mph, maybe squeeze 102 out of it, since I did the 3x3, MRD and Jetting it wont go past about 90MPH, does this mean the main jet is also too small??


Current Mod status



JD Jet kit

extended fuel screw


Blue needle, 3rd clip

125 pilot

155 main


Any help would be appreciated.

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