Do i have to play with air/fuel mixture screw if i put a 42 pilot jet on????

[400exBro]

I heard that if you put a 40 or 42 or higher in you might have to play with the air/fuel mixture screw, is the neccessary or should i leave it at the 3.5 turns that the K&N power kit told me to switch to ????????
if so how many turns out should it be on a 42 pilot jet?????
thanks
400exBro

[quadfamily]

I know you're talking about a 400EX here but I installed a 42 pilot (2 sizes bigger than stock)on my 300EX and I never touched the screw. Mine is still set as it came form the factory and I do not have a K&N jet kit. I have raised the needle and went up around 4 or 5 main jet sizes also. I know we don't have the same quads but maybe this will help you in some way? After all jets are jets!

[400exBro]

I got a 400ex and hopefully i just got to put in the pilot jet because i dont want to play around with the main jet and needle again
lata
400exBro

[knighttime]

That screw seems like the cure-all but dont go crazy. Put it on the stock position before re-jetting (2 1/4 turns out). But you have the k and n so do what they say to do. K and N are smarter than u and me and even Rico, lol. Just dont tighten that screw too much while seating it or u will have it all screwed up.

good luck,

mike

p.s. My quad runs good with the below setup and I have the fuel mix screw at the stock position. Wait, I think i cheated a little and have that screw at about 2 1/2 turns out.

400exBro -

What leads you to believe that you need a #42 pilot jet in the first place?

With most minor mods, you can leave the pilot jet stock.

If you're planning to rejet because of a pipe addition, you need to focus on the main jet. Raising the needle one notch is also recommended.

Without going into great detail, dialing in the main jet is straightforword. First, raise the needle by lowering the clip one notch. Then, buy a bunch of main jets in incremental sizes (#158, #160, #162, #165, #168, #170, #172). Put the biggest in, if it stumbles hard (won't miss it), then put in the next smaller size. Do this till it runs smoothly from bottom to top of the RPM range. That's the right jet. You want to get it to stumble at first (with the biggest main jet), that'll give you a reference point. So if it doesn't stumble with the #172, go get a #175, etc.

Anyway, since you didn't mention you're rejetting because of a pipe, I'll assume you want to increase the pilot jet because of hard starting.

It most likely isn't necessary to increase the pilot jet with stock and even mildly moded (pipe, filter) motors. You need to turn your air/fuel mixture screw out 1/2 to 1 turns out - that'll help it in starting. The screw is located under the carb, directly in front of the floatbowl.

Some adjust it by have the quad running, and turn the screw out till the engine runs the best. After that's done, and you're trying to correct for a lean bog right off idle, then its a good time to increase the pilot jet's size. After installing the new pilot jet, you have to start over with the air/fuel mixture screw - adjusting it till it runs the best.

With that said, that level of tuning isn't necessary to most riders. Just turn that air/fuel mixture screw out 1/2 to 1 turns out, it'll start much better.

ogre

[400exBro]

Thanks all for helping me...
I have rejeted when i put the pipe on a long time a go i run a 160 main 3rd notch on the needle clip just like K&N said to do. then i played with the air/fuel mixture screw and it wont start with out full shocke and it still might not start right away. so i decide to buy a 42 because it is supposed to cure the problem..
Also in the summer i need chocke some times to get it started so now in the winter with -15 degrees celcuis it probly wont even turn over so i think that this was a smart investedment
lata
thanks
400exBro

[quadfamily]

I forgot to mention that my quad had a hard starting problem from the day I got it (used). Like you I had to use the choke even in warm weather. Then even after it warmed up and riding for a while if I let it sit and idle it would stall in a minute or so. Since I put my 42 pilot jet in it starts up perfectly with NO choke and idles right away.

400exBro -

Great, sounds like you've exhausted the air/fuel mixture screw adjustment options with the stock #38. When you go up to a #40 or #42 (like quadfamily mentioned), this is how I've heard to dial it in. (by the way, this is kinda a repeat of what I mentioned before - but I'll be more clear)

After installing the new pilot, give the air/fuel mixture screw about 2 turns out from a lightly seated position. After the quad is warmed up (may want to ride it around a bit), carefully reach in there (the header pipe is hot) while the quad is running and turn the screw out and in. You want to find the setting that the quad idles highest and best at (read as - runs the smoothest). Obviously, you don't want it to run super high, that indicates a lean setting. You'll know what I'm talking about when you play around with the adjustment.


Oh, and by the way, needing a little choke on start-up is normal. If you compensate too much, your quad will run rich at idle when fully warmed and may cause stalling. I'm sure you'll find a happy medium though, everyone that plays around with this setting does - just learn as you go.

have fun,
ogre

a 42 pilot will do wonders for your cold starting, and it may help keep your engine cooler if you do alot of low rpm trial riding too.

[400exBro]

007 enough- i do a lot of slow tight trails riding as much as i love to ride mx(maybe mx a lot more than trails) so i hope that the 42 will kool the engine at low rpms

Ogre- you are saying that after i install the 42 pilot jet that i should leave it at the 3.5 turns that k&n told me to do then ride around for a while and the play with the air/fuel mixture screw until i notice it idle perfect or near perfect and go from there. also i belive that the air / fuel mixture screw is on the left side of the carb(shifting side , where the chocke is) i could be wrong its been a while since i played around with it???
thanks all for help
lata
400exBro

400exBro -

Start with 2 turns out, not 3.5. It's best not to listen to K&N's (actually dynojet's) instructions. Listen to your engine, it'll tell you what it wants.

With 2 turns out, let your machine fully warm up, then play with the setting, noting how much you turn it each way (so you can keep track of the starting position, which is 2 turns). As you turn it out, the mixture will get richer, turning it in will lean the mixture.

The air/fuel mixture screw is located under the carb, directly in front of the floatbowl (it's slightly sunk, so take a good look where it actually is). You'll see it when you flip your carb when you take the floatbowl off to access the pilot jet. Also, after remounting your carb, you'll be able to do subsequent adjustments to the mixture screw without removing the carb - you just have to find the right sized screwdriver.

Do NOT mix the air/fuel mixture screw up with your idle speed adjustment, that's the one you're referring to, next to the choke lever. You won't need to adjust the idle for this procedure.

ogre

[400exBro]

Thanks a lot man you really helped out on this one!!!! :D :blah Hopefully it will be in this week so i can get her in before the weekend so i can ride
thanks
400exBro