350x airbox questions

[camoweasel]

So far, my 400ex carb seems to really be working. As of now, I am still running airbox lid. I've done a few WOT passes to determine if having an airbox lid is worth it or not. Well my conclusion was that with or without the lid, I couldn't tell any difference between the two. Right now I am running a Uni filter but with only a few hours on fresh cleaned Uni, it got really sandy and dirty making me hesitant about running without the lid. Basically my question is to all those with the 400ex carbs: Are you guys running a lid and if not, do you think it makes a difference?? And isit worth running an outerwear on Uni when not using lid?

My current setup:
99 400Ex carb
fuel screw: 2.5 turns out
pilot: 42
needle: 3rd clip from top
main: 165
airbox lid on

I tried a 172 main today, but it seems like my plug is starting to turn black when doing 1/2 throttle chops. The 165 seems to pull hard and strong with or without the lid.

[camoweasel]

Basically all I'm asking is are there any significant gains to running without the airbox lid and is it neccessary to run an outerwear on a Uni filter if not running the lid?

[AJZ_200X]

I have the same setup / jetting etc. Ive kept the lid on since ive made the switch. The performance difference really is minimal with the lid off. Ive seen guys cut holes in the lid to increase airflow, but I think its useless to do so and a waste of a lid :rolleyes: If you ride were gunk will get inside, then keep it covered. If you prefer to ride without a lid, I would suggest soaking filter in filter oil that you can get at your local motorsports store which will catch small particles.

[AJZ_200X]

** And stick with the 165 main

[Dirtcrasher]

Your lucky! My bikes are totally different jetting if I wanna run the lid, I never run the lids............

Without a lid, you should be able to go even a bit richer on the jetting.

[390x]

In my experience DC is right, I had my storker motor (the 390) set up with holes in the lid behind the filter. With the holes at the back, it sheltered the filter pretty well, it still got dirtier than with a sealed box. In the summer I ran a UNI filter, oiled of course. In the winter I run an oiled K&N, no dust in the winter, it's either wet or frozen. No outer wear on either. Your riding areas may dictate a different arangement.

When It was jetted correctly, it was slower if I taped the holes closed, and w/o the lid it would ping the tiniest bit at full throttle cresting the top of the bigger hills. I spent ALOT of time messing with the jetting on that set up. The key for me to get it right was to test it exactly the same each time making only one change at a time. Then when temp changes, you do it all over, around here it is 100 deg F in the summer and when it snows I ride in temps as low as single digits.

With that motor the 350X carb felt like it was either on or off, the 400EX carb, once it was tuned was much more user friendly and made way more power.

[camoweasel]

Well believe it or not, when I had the 350 carb, I was running a 160 main jet. Reason being cause I'm at sea level and I had a port job done with amazing results. When I bought the 400 carb, it had the 165 already in it and so far seems to be working well. I mean if I really wanted to, I could probably try the 168 or 170 but seems to be burning at a light sandy brown color at all throttle ranges. I may try to experiment more with the lid and see if anything else changes. I just couldn't believe how dirty the filter got by riding for an hour in the sand!! Even though it was just cleaned and re-oiled it still made me nervous.

I am also running a DPR8EA-9 instead of the factory D8EA plug. It's basically the same plug except that it's a projected tip plug meaning the insulator and electrode stick further down in the combustion chamber. Even with my 10.25 piston there still seems to be clearence. Plus it's easier to read plugs with more of the porcelin exposed to the flame kernnel.

[390x]

If it were me, I would buy the other jets and try them with the air box/fiter set up you intend to use. The right one will perform the best at WOT. Each jet size will make a difference that you will notice good or bad, if you test each one the same way. I would not worry so much about 'reading the plug', as it is very difficult at best with todays fuels, it can give you a rough idea though.

I would get the main right, then go back and mess with the needle. The main jet affects anything over 1/4 throttle. Needles with different lengths/tapers are available if you find that you can get it good at 1/3 throttle but not 2/3 or vice versa.

A couple good reads:

http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf

http://www.carbparts.com/keihin/needles_tuning/jetting_your_carb.htm

[camoweasel]

If it were me, I would buy the other jets and try them with the air box/fiter set up you intend to use. The right one will perform the best at WOT. Each jet size will make a difference that you will notice good or bad, if you test each one the same way. I would not worry so much about 'reading the plug', as it is very difficult at best with todays fuels, it can give you a rough idea though.

I would get the main right, then go back and mess with the needle. The main jet affects anything over 1/4 throttle. Needles with different lengths/tapers are available if you find that you can get it good at 1/3 throttle but not 2/3 or vice versa.

A couple good reads:

http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf

http://www.carbparts.com/keihin/needles_tuning/jetting_your_carb.htm


I agree with your advise but it's really hard for me to tell if the different jets work better or not cause it seems like power is the same. I guess, I'll try some more jets and see what happens. I just happened to have a 172 laying around. Next i'll start messing with the needle and see what happens.

[390x]

I agree with your advise but it's really hard for me to tell if the different jets work better or not cause it seems like power is the same. I guess, I'll try some more jets and see what happens. I just happened to have a 172 laying around. Next i'll start messing with the needle and see what happens.

The key is to standardize your testing, pick a hill or hills and test each throttle position the same way in the same spot after each change. Keep notes if necessary, my memory is not the best. Try to make sure the engine is warmed up, but not running hot. Jet with clean air filter, then install clean filter before you ride to get all the performance you worked for when jetting. When jetting, be mindfull of ambient conditions, dry sunny day is way different than rain, even if temp is the same. Just because you get it right, don't be afraid to change or at least try a change later. With some effort you will get used to what it needs for various temps/conditions.

[camoweasel]

Well today after some more testing, I have determined that running without the lid does offer a bit more performance in the top end. I also retried the 172 to see if there was any improvement and to my suprise, I could definitely feel more top end power. Like you said, it's hard to judge just by the plug color, because I really can't get the plug to change colors. I even bought a new one which was harder to read, because it still looks brand new. I'm pretty sure the needle is set right because the last time I moved the needle up, it seemed like the throttle response lacked when I wacked the throttle. All and all I'm pretty impressed that its running a 172. The guy who ported my head even said about how much metal he took off the ports and how the flow bench results spiked. But maybe with some more testing I'll try another some higher jets to see how it performs. The only noted difference in weather today was that it was about 10 degrees cooler which hopefully doesn't change to much by he next day.