Ran badly at altitude today. Advice? - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 24 Old 08-11-2013, 10:26 PM Thread Starter
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Ran badly at altitude today. Advice?

Rode my 2003 up the mountains today. Ran just fine till I got to about 10,500 ft. There's a 15% + grade and I was WOT. Bike started surging and temp gauge got just to the low end of the red bar. Stopped as soon as I could let it idle till it cooled a bit. Ran great downhill and for the rest of the day at 8000'

Cooling system seems ok-stays cool at 105 F at 5000' in traffic.

Not sure about PO mods but the pilot screw cap hadn't been drilled out, so suspect 22 cent mod hadn't been done. I have backed out the mixture screw to 2 1/4 turns from 1 1/2 & it runs fine at part throttle below 10,000'

So I'm puzzled. It acted like it was running lean (surge & overheating) and at WOT I wouldn't expect the mixture screw to be doing much.

What should I investigate first?

Thanks in advance , Wray
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post #2 of 24 Old 08-12-2013, 12:29 AM
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Hi UncleWray!
The higher the elevation, the thinner the air, the richer the mixture runs. If the filter is dirty the mixture is richer again. The Factory KLR needle is excessivly rich at WOT as well. At higher elevation you need to lean the mixture. Some have done this by removing the airbox door while at high elevation.
I suspect the heat was caused by overworking the engine at too low of rpm.(just a thought) Drop down a gear and let it rev a little more, perhaps at a reduced speed.
Regards....justjeff

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Last edited by justjeff; 08-12-2013 at 12:31 AM.
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post #3 of 24 Old 08-12-2013, 06:40 AM
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Fuel screw ("pilot screw") only dominates mixture at idle.and vicinity



Even fuel-leaning the mixture at altitude, lower oxygen partial pressure up there means less fuel processing per unit time, aka . . . less power possible. Fact-of-life for all naturally-aspirated internal combustion engines, sorry!

BETTER combustion is possible by fuel-leaning the mixture at altitude, but . . . the process has its limitations.
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post #4 of 24 Old 08-12-2013, 06:41 AM
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Is your air filter clean?



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post #5 of 24 Old 08-12-2013, 10:15 AM Thread Starter
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I had cleaned the air filter (UNI, I think) a week or so ago. On advice from the Internet machine, I oiled it with some spray from Bike Bandit made for filters. When I oiled it, I asked myself, how does air get through this... Stuff was very tacky and thick.

Maybe I should try some Mobil 1 thin stuff? Or maybe I put on too much?
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post #6 of 24 Old 08-12-2013, 10:21 AM Thread Starter
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Re: gearing--I was in second & not going very fast, probably didn't downshift to first soon enough. The speed limit is 35 because there are cliffs where you can learn to fly on the way down.

BTW, this is the same hill that my ancient Ford 4x4 really dogs on.
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post #7 of 24 Old 08-12-2013, 10:26 AM Thread Starter
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Quote:
Originally Posted by Damocles View Post
Fuel screw ("pilot screw") only dominates mixture at idle.and vicinity



Even fuel-leaning the mixture at altitude, lower oxygen partial pressure up there means less fuel processing per unit time, aka . . . less power possible. Fact-of-life for all naturally-aspirated internal combustion engines, sorry!

BETTER combustion is possible by fuel-leaning the mixture at altitude, but . . . the process has its limitations.
Thanks for the graph, been looking for one like that. So mixture screw is not in the picture at WOT. To change anything, looks like I need jet and taper. I'll try the other cheap stuff first (oiling of the filter, better gear selection), but that helps me know where to head.

I think I've seen jet and needle sets--any recommendations on what sets to buy? or should I just buy a couple of jets and try them?

Thanks!
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post #8 of 24 Old 08-12-2013, 10:28 AM
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also make sure your tank is venting well .. if not it will act like your running out of fuel .. old dirty gas caps and vent tubes is where you can look..

im here in Colorado springs and ride into hills every weekend with my bike still on stock settings ..

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post #9 of 24 Old 08-12-2013, 10:44 AM Thread Starter
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Quote:
Originally Posted by justjeff View Post
Hi UncleWray!
The higher the elevation, the thinner the air, the richer the mixture runs. If the filter is dirty the mixture is richer again. The Factory KLR needle is excessivly rich at WOT as well. At higher elevation you need to lean the mixture. Some have done this by removing the airbox door while at high elevation.
I suspect the heat was caused by overworking the engine at too low of rpm.(just a thought) Drop down a gear and let it rev a little more, perhaps at a reduced speed.
Regards....justjeff
Question on the airbox door--should I go ahead and do the snorkel/ drilling of the airbox mod? I've been hesitant to try some of those things--afraid that they work at sea level, but I only ride in the 5000-12,000 foot range.
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post #10 of 24 Old 08-12-2013, 11:09 AM Thread Starter
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Quote:
Originally Posted by wayne_l View Post
also make sure your tank is venting well .. if not it will act like your running out of fuel .. old dirty gas caps and vent tubes is where you can look..

im here in Colorado springs and ride into hills every weekend with my bike still on stock settings ..
Good thought on the venting--bike is new to me & pretty sure the PO(s) didn't take care of that stuff.

In fact, the first thing I said when it was surging was "how could I be out of gas?"--moved the petcock to reserve & didn't change anything cause I wasn't out of gas. I get out the Clymers and see where I should check.

Thanks!
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