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Ok I have read alot of different things about carburetors needing to be rejetted when you go riding in high country. Is this really necessary? Would anyone like to share their opinion on this? We are looking at Colorado and I am confused about this. Thanks in advance. KLRed.

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I guess your KLR would has a CV carb, which is altitude compensating to a certain degree. Your HP is going to be down from from what you are used to. I don't use a cv carb, and I want maximum performance and fuel economy so I usually drop two sizes on the main jet and don't go much below 8000 ft. It's a compromise, you'll be up and down so much but changing jets for every 1000 ft elevation change just isn't practical.
The 08 TE610 I had with EFI was the cleanest running bike I've ever had, ran perfect everywhere. If you keep your air filter clean you may get by OK, my old xl600's was so tiny, I'd have to clean it every other day.

First, you will lose horsepower at altitude because of lower air pressure (fewer oxygen molecules per cylinder volume) requiring fewer gasoline molecules. No fix for that other than a turbo or supercharger.

Second, a CV carb tends to be more forgiving of altitude changes as air pressure is what moves the main needle up and down. The throttle opens a butterfly valve but does not actually move the needle. As you go up in altitude the air pressure drops so the slide doesn't pull the needle up as far so the amount of fuel decreases which keeps the oxygen / fuel ratio close to correct. On a performance / pumper carb the throttle pulls open the slide / moves the needle directly. Thus the mixture gets too rich.

Third, from what I have been told the larger the displacement the less problem with altitude changes. Smaller displacement motors are much more in need of corrective jetting changes. Your KLR is large displacement.


I can tell you what I did with my KTM LC4 (cv carb: Mikuni BST) and what I do with my KTM RFS (Keihin FCR / FCR MX). You may need to adjust either when you get there.

CV carb: drop the needle one or two grooves. Adjust the fuel screw and idle when you get there. An extended fuel screw helps. Also can microtune using the fuel screw during a ride if it is an extended type.

FCR carb: drop the needle two or three grooves, lean the main jet a few steps. Adjust fuel screw and idle when you get there. Extended fuel screw is again a plus.

Safiri knows what he's talking about -- both from a pure science perspective and real experience. He's camped off the bike for 7 days up there.

I rode my old 1999 DR350 for a week in altitude ranging from 8,500 all the way up to almost 13,000 (Hermit Pass, ended in snow). It was just fine. Above 11K or so it was definitely weak--very weak at the top, but running fine and getting me where I wanted to go. I did not mess with the jetting at all.

Like, Katbeanz, my fuel-injected TE450 was a dream at altitude. However, that machine had other issues that made me welcome it's departure.

You can't "drop the needle one or two grooves" in a klr if your carb is stock. The needle doesn't have grooves in it to adjust fromt he factory unless you have installed a jet kit.
The klr is already lean from the factory, so about the only thing you may find yourself doing is taking the door off of your air filter housing to let the bike get more air. Other than that, i'm pretty sure you will be just fine. There is a ton of info over on klr650.net if you need to research further.

Edit: if you do decide to change to a smaller jet once you get up there, be very careful of the screws holding the fuel bowl on to the carb. they will be siezed up, and the screw head may strip out on you since they are phillips head screws. This man http://www.eagle-m-e.com/productlist.htm can overnight you some stainless hex head screws to replace them with before you go. Swap the screws out now while you have other tools available. I ended up having to use a dremel and a cutting whell to slot one of the screw heads to take a straight slot screwdriver.

If your bike is stock you're in luck because it's lean. So in CO it should have a little more rich setting, but like others said it will feel weaker. Whether you go to CO or not I would do the .22 mod, richen the fuel screw and do the frugal exhaust mod. It's dirt cheap and it gave my 08 KLR quite a noticeable difference.

JasonK94Z wrote:You can't "drop the needle one or two grooves" in a klr if your carb is stock. The needle doesn't have grooves in it to adjust fromt he factory unless you have installed a jet kit.

Wow. I guess that is yet another way to keep folks from messing with jetting. Of course a rider doing Death Valley and Leadville probably won't be happy with stock jetting both places.

If you do mess with the main jet, it sounds like you should do that NOW, weeks in advance, so if those screws get messed up you can get the problem fixed.

Kawasaki parts manual will list high altitude jets, main and pilot. Pretty easy to change out and the difference in performance is noticeable.

My wife and I just took a Sherpa and a DRZ400E to Colorado. I had previously jetted them on our dyno (these bikes come set up too lean). I took spare pilot and main jets with me but both bikes did ok with their Kansas City jetting and I didn't have to touch them while we were there.

That being said, every bike is different. I have to say that based on what we see that a lot of the jet kits out there result in a bike that is often on the rich side; so if you've installed a kit you may have issues at altitude.

Kawasaki parts manual will list high altitude jets, main and pilot. Pretty easy to change out and the difference in performance is noticeable

There's the answer right there!
I would run to the bike shop and buy the main and pilot jets, and if you don't already have them, definately buy the stainless hex head bowl screw set and an extended fuel screw so you can dial it in when you get there. Probably get all that for about a 20 dollar bill.

My DRZ has the air box opened up, larger main and pilot jets and a power tip to open up the exhaust. I never spent the money on the jet kit or aftermarket exhaust and it runs awesome around here. I have taken it to Colorado with Troy a couple times. Although I do have an adjustable needle, I didn't mess with it. Because of the air box mod, just putting the stock jets back in worked great...all the way up to 13,000 feet with little although noticeable power loss. At 8 to 10000 ft. the fuel/air ratio was spot on.

Good luck and look forward to a ride report!

Greg Williams wrote:I had previously jetted them on our dyno (these bikes come set up too lean).

Ok, I'll bite ... "our dyno"?

safiri wrote:

Greg Williams wrote:I had previously jetted them on our dyno (these bikes come set up too lean).

Ok, I'll bite ... "our dyno"?

What?! You don't have your own dyno?! Who doesn't these days? I have 2.

safiri wrote:

Greg Williams wrote:I had previously jetted them on our dyno (these bikes come set up too lean).

Ok, I'll bite ... "our dyno"?

Yeah. Inquiring minds want to know!

My carb has a stage 1 jet kit in it, and I think its off some, especially when idling. In the morning, on the enrichment circuit, it smokes now.

I had a Dr650 that fogged the area when I started it on full choke. Found out with a jet kit and choke, it was so rich, it washes the oil off the cylinder.

safiri wrote:

Greg Williams wrote:I had previously jetted them on our dyno (these bikes come set up too lean).

Ok, I'll bite ... "our dyno"?

I work with Cafe Racer in Kansas City. We run a Factory Pro dyno.

MacWildcat wrote:I had a Dr650 that fogged the area when I started it on full choke. Found out with a jet kit and choke, it was so rich, it washes the oil off the cylinder.

Ouch! So the fix? Maybe move the clip on the needle up one notch?

Affirmative, Jason. She definitely needs to be leaned out a bit. After you adjust the needle, you may want to tighten up the pilot screw (low speed circuit) to get a smooth idle.

Aside, I'd encourage all to visit Cafe Racer (Thanks Greg). A very cool shop with some great folks. These guys specialize in road racers and always have some really nice bikes on the floor...

KLRed:

I just completed an indirect ride on my 07 KLR 650 from SLC, UT to KC via CO. I too was concerned about my stock carb's jetting, but the KLR did fine. I'd do it again thru those mountain passes w/o re-jetting.

One word of caution: I did not ride the interstates, so my speeds were mostly 65 mph and below. My recommendation is try it stock first.

Best regards!

Greg Williams wrote:

safiri wrote:

Greg Williams wrote:I had previously jetted them on our dyno (these bikes come set up too lean).

Ok, I'll bite ... "our dyno"?

I work with Cafe Racer in Kansas City. We run a Factory Pro dyno.

Can I ask how much that costs without incurring Troy's wrath? I met the guy that does the chicken noises once, but forgot his name.