Carb jetting for altitude? - Kawasaki KLR 650 Forum
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post #1 of 13 Old 07-05-2016, 03:23 PM Thread Starter
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Carb jetting for altitude?

Reaching out to you rocky mountain riders with a question. My 08 KLR is stock jetting and runs nicely in my home terrain which doesn't exceed 4000 feet. Do I need to change from stock jetting for the altitudes in CO? If so, what is recommended? I am riding the COBDR later this summer? Thanks!!
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post #2 of 13 Old 07-05-2016, 03:32 PM
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Originally Posted by shaoul View Post
Reaching out to you rocky mountain riders with a question. My 08 KLR is stock jetting and runs nicely in my home terrain which doesn't exceed 4000 feet. Do I need to change from stock jetting for the altitudes in CO? If so, what is recommended? I am riding the COBDR later this summer? Thanks!!
I live at 7800 ft,. I HIGHLY and REALLY recommend the kit upgrade from Eagle Mike's.. I went, as a starting point, just as recommended. And I was amazed at the improvement for the bottom end. I also got 39.9 MPG at 70 doing additional climbing.
It is a must in my opinion. If you want to just try the jet,, 140 is what I used..
Go enjoy... And know there are those that are jealous of the area...
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post #3 of 13 Old 07-05-2016, 06:24 PM
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For a tourist run up to Colorado, I would not change jetting.

If I LIVED at altitude, like Squidly at 7800 feet, I would give the prospect serious consideration!

Here's my rationale: A CV carburetor performs some "automatic" altitude adjustment on its own; less dense air at altitude pulls less venturi vacuum at the same intake air velocity, thus: A more fuel-lean mixture at altitude, livable for a short stay in, say, Denver.

Loss of power? Inevitable at altitude even with optimum mixture anyway, but livable 'til you come down the mountain, I'd think.

In the bad old days, when automobiles had carburetors, don't know of any tourists who re-jetted their carburetors for a vacation trip to Denver, Colorado Springs; even up Pike's Peak!

Now, maybe motorcycles are different. Maybe the loss of power due to excessively fuel-rich mixture is so great, re-jetting is mandatory. I doubt it, but . . . never rode a motorcycle up to the Mt. Everest base camp, either!

So far, my random thoughts and abstract analysis--I defer to those who have actually ridden KLR650s at altitude.

Just thinking . . . did/do carbureted airplane piston engines have variable fuel mixture control in flight, say from sea level to service ceiling?
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post #4 of 13 Old 07-05-2016, 09:15 PM
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Originally Posted by shaoul View Post
Reaching out to you rocky mountain riders with a question. My 08 KLR is stock jetting and runs nicely in my home terrain which doesn't exceed 4000 feet. Do I need to change from stock jetting for the altitudes in CO? If so, what is recommended? I am riding the COBDR later this summer? Thanks!!
shaoul,
As suggested by Damocles, the stone stock KLR650 is perfectly capable of riding the COBDR or Ouray/Silverton/Telluride area with stone stock jetting. Even at California Pass, elevation of 13,600 I think I remember.

The one thing that I will suggest is, Turn-Up your Idle Speed to 1300 +or- 1000 with fully warm engine. It will start better. And it can be Totally Normal to need to use Choke after just a 20-30 minute lunch break in the cool mountain air!

One more note, Do Not just tap and release the starter button!
Crank IT! The system is not like a car, it will not 'grind the gear'.
If you attempt a warm/hot start and it doesn't immediately start, gently open the throttle a 'smidgeon', while still cranking. This procedure increases the 'cranking engine Compression' and slightly 'Leans' the low speed mixture.

So I now count 3 very minor 'tips', with Zero wrenches.

Ut Oh!
Tip #4 involves wrenches,
Check your Valve Tappet Clearance and set to the Wider end of Specs if you haven't all ready done so! Especially the RH Exhaust Valve. Why? To ensure the most Cranking Compression! And is just 'Good Maintenance'.

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 85,000+ miles & counting
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post #5 of 13 Old 07-06-2016, 09:57 AM Thread Starter
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all, thanks for the feedback. Still undecided will let you know which way I go.
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post #6 of 13 Old 07-06-2016, 10:53 PM
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Cool; your call!

No matter what you do, you'll lose power at altitude.

And . . . should you re-jet, you'll need to restore lower-altitude jets when you return home.

Maybe this is a job for, "Dial-A-Jet!"

Regardless: Your bike, your call; best wishes, let us know how the trip went.
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post #7 of 13 Old 07-07-2016, 11:39 AM
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Yep, I'm with Paul and Damocles; the CV carb is self-adjusting for the most part.


Dave
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post #8 of 13 Old 07-07-2016, 11:51 AM
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Having ridden at elevations over 10000ft in the Canadian Rockies I see no need to rejet for a holiday. I might think of removing the airbox door for a temporary leaner mixture but would only rejet if I was living there. If you are just going through mountain passes the KLR has plenty of power even with a slight loss on being rich at high elevation. From stock KLRs are jetted lean for emissions so running at high altitude is actually compensating for the overly lean emission jetting. I notice very little power difference on my '11 while at altitude.
JJ
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post #9 of 13 Old 07-09-2016, 08:45 PM
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I live in Colorado at 6,000 ft and ride an '06. I've ridden both the Great Divide and the TAT and never touched the carb. My son did the same on a '14 NE and also had no problems. Would they have had a little more performance if we had been changing jets? Maybe, but we were both happy with stock and they both ran fine from sea level to the highest passes. If you're a gear head and like playing with it, do it. If not, you'll be fine.


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post #10 of 13 Old 07-13-2016, 11:52 AM Thread Starter
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Thanks to all that weighed in on this. You've given me the confidence to go stock for the week. Or perhaps just gave me enough validation of my desire to not mess with the jets. There are always various opinions and my riding buddies were all suggesting re-jet. Of course if I run into any problems I won't expect much sympathy from them! Will give a ride update at the conclusion of the trip.
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