I have an 07 z400 and recently put an FMF Factory 4 slip on with mid pipe. I have a KN air filter with the stock lid. I think my jets are off or not enough air is getting through because it is "backfiring" in 2nd gear. My questions are:

1. Anybody know any suggestions for the jets?
2. Will any dyno jet kits help hp and performance? If so which ones?
3. Is it best to just remove the air lid or make bigger holes in it?
4. Will the trail tech thingy work on the z? If so where does it mount?

Thank you fellas, appreciate it

 

Geeez it's been so long since I jetted my Z, but I'm fairly sure the main jet is a 165, had to turn the air screw out some, and I have opened the lid.

 

I have an 06 Z and it is very tempermental. The most I have gotten away with without jetting is when I removed just the spark arrestor fron the pipe. Once I didn't get my lid down tight on the air box and it ran like crap...backfiring, popping, etc.. So I contacted someone about this and they had told me that jetting is a requirement for almost anything done to these engines. Now, I'm good...it's just a PITA changing them and pulling the plug since it's not the easiest thing to get to. Your plug will tell you everything. Learn how to read it... Too lean is very BAAAAD.

The backfiring is due to a lean condition and it's detonating. 1. jet it richer 2. a good leaded racing fuel will make a world of difference (VP C-12) You should mix it 70% 93 octane to 30% VP. It will def. help.

As for a jet kit, jetsrus.com
read all you can on this site.

 

I checked out jetrus.com and found a jet kit that looks like it describes what I need but it says for a 03-06 z400 not an 07. Will it still work? Here is the jet kit I was looking at:

Suzuki LTZ400 jet kit $31.99

The jet kit comes with all the following brand new parts: Genuine Mikuni precision machined main jets: 140, 142.5, 145, 147.5, 150, 155, 160, 165 and 4 stainless steel allen head bolts for the carb bowl. Instructions on jetting included.

This kit is for modifications such as the following: aftermarket air filter, air box lid removed, modified air box, aftermarket slip-on exhaust or completely modified exhaust or cams.

 

yes

 

ok thank you. Now I just have to figure out how to do it. Also, how do you remove the spark arrestor?

 

to remove the spark junk, just take out the 3 allen screws on the end of the pipe and yank it out. You will notice a huge gain just from that. The jetting is easy but kind of a PITA. The plug is a bigger one. The way to change jets: shut off fuel, loosen bowl drain screw, drain fuel, loosen clamps, turn carb sideways remove the float bowl, unscrew the jet put in new one, replace bowl using new s/s screws, close drain screw, turn on fuel. If you did just minor mods, go up 2 from stock, better to be rich than lean. Put in a new plug to begin tests. Run it kinda easy to see how it reacts. Pay attention to the temp of your head pipe and if your fan kicks on more than normal. If it gets hotter than normal, you're lean. Check the plug. If it's very white, go up 2 more sizes, tan, your good, sooty black and wet, too rich. I like mine a little black to keep it rich for top end drag racing. You can keep using the new plug, just clean with a brass or nylon brush. DO NOT use any solvents. it'll foul the plug. But you at least want a new plug to begin new jetting tests with.

 

Awesome! Thank you for all that helpful info. To tune the jets if I just get the jet kit I will be able to do it, don't need anything else, right?

 

just a new plug. Depending on where your located, Elevation wise, You may want to experiment with pilot jets but there's really no need. I noticed that it ran kida rough during the winter and the pilot jet was the reason but after it got up to full operating temp, it was good.

You <u>may</u> have to mess with your air bleed screw, but that's usually not necessary.

 

I'm pretty sure you need an adjustable needle too. If i was you i'd buy a jetkit from dynojet or alba. They come with a bunch of main jets( more then you need) and a needle. You will need to adjust the Fuel screw at the bottom of the carb too.

backfiring on decel is a sign of a lean engine. The stock main jet is 130 in your z400. I'd put in a 155 main, needle on 3rd clip and fuel screw 2 turns out. You have to remember Mikunki jets and Dynojets are not the same size. So which ever kit you get, make sure you know what kind they are.

doesnt it come with a jetting recommendation wit that FMF pipe?? Also check your plug, you want a nice brown colour, dont always completely depend on it though, it isnt the most accurate thing for checkin jetting, but it definatly gives you a ball park figure.