[Upsandowns]

I live in Western NC at approx. 2,300 ft above sea level, but it's only minutes to be at almost 6,000 ft. While riding the Blue Ridge Pkwy the other day on my new 2009 DR-Z400S Dual Sport, I noticed a brief hesitation in the engine when I tried to accelerate beyond 55 mph in 5th gear at about 4,200 ft. The hesitation continued to occur each time I tried to accelerate, and became worse as I passed the 5,000 ft level and after about 5,500 ft, I couldn't accelerate in either 5th or 4th gear, and the engine seemed a bit anemic. It continued to run smoothly, but it lacked any enthusiasm unless I was going downhill. I'm in a quandry - what does one do when any given ride can find the bike going from about 1,000 ft above sea level up to over 6,000 at Mt. Mitchell ???? If I make the mods, whatever they might be, for 6,000 ft, I'll have problems back at 2,300, and if I leave it as it came from the dealer, I have to accept issues at higher altitudes. Is there an acceptable middle of the road? If so, what do you recommend??? I know if I take the bike to Colorado, I'll have to do something drastic, but that will be the exception. It's the daily riding in my own backyard that concerns me. Thanks for your insight. Upsandowns:ride:

[clrwatrtom]

i rode the Cherahola Skyway at Labor day this year with sea level jetting and i had no problems at all and i saw 5490' elevation. my bike is stock internally, but i do have a k&n, 3x3 mod. 39mm FCR and an open Yosh RS-2.
is your bike stock?(pipe and carb)

[Eddie Sisneros]

you jet for the elevation you ride the most and deal with it not being perfect everywhere else unless you are there long enough to rejet.


in your case,just pull the rubber snorkel out of the intake hole and and continue about your normal business.

[oldmanb777]

The stock S is pretty altitude tolerant. Pull the snorkel or 3x3 mod. Expect it to not be perfect when off the "density" altitude you are jetted for. You just have to compromise for that. I find that after the JD jet kit, it became more intolerant of altitude changes.

[Roadracer Al]

I often pop the airbox lid off at altitude, and put it back on when decending. It's a big change.

[Upsandowns]

Many thanks for all of the suggestions. The bike is completely stock at this point. The next time I'm up on the hill I'll give the snorkel removal a try as well as removing the airbox lid. It's possible that I overstated the problem, but it was frustrating when I couldn't keep up with my son on an efi V-Strom and when I went over 4,000 ft my bike just didn't want to go as well as it does at lower elevations. I had expected something like this and was watching the altitude read-out on my ZUMO gps so I'm fairly sure my altitude observations are reasonably accurate. Once again, many thanks for your recommendations.

[jbwiden]

I want to buy a cheap air box cover that I can put some holes in so If I do go up to high elevation I do not have to rejet. Just grab the other airbox cover and ride. But it seems like nobody is selling.

Jbw

[GOF1]

Didn't someone do something with holes in the airbox cover and some kind of plugs? I remember the conversation. There was talk of a vent setup like that on a Weber grill. Wonder how that ever worked out?

[Upsandowns]

Once again, thanks for the ideas. One of the things available on the market and sold by Rocky Mountain ATV are "Uni Filter Air Box Vents" item #1068750001 and you get about 6 of them for $11.00. This, certainly, would be an inexpensive approach, and, if it worked, about as simple as it gets. I'm a little reluctant to start cutting holes in the body panels and may start with a K&N filter and enlarging the hole in the airbox, although at least one fairly knowledgeable person has said this would necessitate re-jetting. At least you've given me some alternatives that fall far short of a carburetor replacement or some other time-consumming and more costly solutions that I might be wary of trying to accomplish on my own.

[clrwatrtom]

do the 3x3 mod and get a JD jet kit. it is 75$ very well spent. your bike will run better and you will enjoy it more. the plugs you're talking about buying are pretty much worthless. the 3x3 mode is the way to go. as long as you're riding on road, the k&n will be an improvement too. If you're going to ride off rooad, run an oiled foam filter. it is good insurance against dirt infiltration, which will kill the coating on your valves.

[Roadracer Al]

The webber grill vent idea was mine, never got around to it.

[Rock Monster]

I tried the vented webber idea and it did work. The only downfall is river crossings. Too much water can get in. The best thing you can do is like Eddie said, jet for the elevation you ride the most and then get an extended fuel screw so you can adjust from there to make up for not changing a jet. You will be surprised at the difference a few turns on a fuel screw can make at elevation. Good Luck.