High-altitude 520?

I'm trying to decide between a 400 and 520 EXC for here in Colorado (my old bike was a 300 EXC). Reviews at sea level seem to say the 520 has too much engine for where I'll spend plenty of time (very tight sections, roots, big rocks, slow-going). But I've also heard 3% power loss per thousand feet, so I wondered whether a 520 at 8 or 9 thousand feet is just about the same as a 400 at sea level (and so would be just right).

Comments, ideas, experiences?


Steve Dz.

I have always used a 2% reduction in hp per 1000 feet in elevation. I live at 4500' and ride to 9000' in summer and 7000' (or so) most of the time.

I rode, and still own a '99 300mxc. I bought a 2002 400 SX. It has taken me 2 full months to learn how to ride a 4-stroke correctly. The 520 (to me) is more comparable to a 380, and the 400 is more comparable to a 300. I have owned a 380 in the past, and a good friend rides a 2002 520. I do not need that kind of power. My 400 will do everything I need it to do.

I will give you the heads up on a couple of things though. There is extra hp awaiting you in the RFS'. Re-jetting and aftermarket exhaust will give you major boost in hp! Good LucK with your decision.

Steve, I've ridden my 91 300 EXC for ten years from 4000' to 12,000'. My 400 EXC is very comparable in power with more top end. I do all kinds of woods riding as well as flat out in the praries.I was also looking for a 520 but they were so hard to find, when this 400 popped up I jumped on it. I even continued on the waiting list for the 520 thinking I would know by the end of summer if I would need more power. I'll tell you I'm not even looking back. The 400 is plenty! I used to race enduros and I might again compete. I've got no worries as I can do everything I need with the 400. Good Luck with your decision. Either way, you won't be sorry and you shouldn't second guess yourself.

Hi Steve, I'm riding a 02 400EXC. I think it has plenty for me. Although it is nice to be able to get the front end up over those big roots and rocks with the 520. My friends are running a 150 and 149 main in their 400EXC. I am still running the stock 175, which is way to rich for this altitude(CO). I am going to go down to 150. Hope it makes it easier to get the front end up. If I get in it too quick I have problems. But If I have enough time I can always get the front end up. Even with the stock mains. The plug is smutty black... And I'm getting bad gas mileage compared to my friends. I have ridden their bikes and the faster response makes a big difference. Don't flood… Fly…. Does anyone else any input on this before I get the 150. The 149 doesn't seem to make that much of a difference. Both friends turn the value out a half turn.




My settings:

Stock pilot (48)

OCEMN needle (#5 clip position)

170 main

1 1/2 turns out on the mixture screw

P-38 accelerator pump cover

T-4 exhaust

plug is med. brown (no soot)

When I first got the bike it was just too tame. It also got horrible milage (20mpg). Now it pulls every bit as hard as my buddies 520 in the mid - NOT on top though. The 520 on top is a gorilla! My gas milage is now 28 mpg, and I can lift the front wheel any time I want, even in the lower rpms. It will loft as easy (almost) as my 300.

I tried a 165 main to begin with, and I lost my top end altogether. I live at 4500' and ride this time of year as high as 7000'.

Good LucK!

I've been struggling with the same question. I don't want to find out that the 520 is a wild bull ride in the woods! Throttle sensitivity and control will make a big difference in tight woods with so much power, but I start riding at 7000' and also figured I may be able to "dull" the responsiveness with richer jetting if necessary. Here's a link to an article that suggests the EXC doesn't have the massive "hit" that the SX has.http://www.off-road.com/dirtbike/mar2000/rick/ktm_4stroke/520EXC.html

Hey Strick, it's mtngoat. Yup, I got Orange fever. Loved my XR440, but I've done everything I could and I want more. The KTMs are sweet.

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