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Old 01-04-2015, 09:56 AM   #1
ballistic_ken OP
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Joined: Jun 2007
Location: Farmington, NM....Great Riding
Oddometer: 5,343
Honda CRF 125 Jeting for altitude, 8,000'

Got a new bike for my daughter, and know from experience that it is going to suck riding in CO unless I get it jetted right.

I have done some jetting work on my bike (DRZ400) but that was a kit and I just followed the directions. I can't seem to find a kit for her bike.

Any suggestions or tips?
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Old 01-04-2015, 02:08 PM   #2
Rogue_Ryder
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Joined: Dec 2005
Location: Pinewood Springs, Co
Oddometer: 7,591
Pull the carb and see what's in there now. Then go over to rockymtatvmc.com and get some jets. 2 pilots and 2 mains going the 2 next lower sizes that are in the bike now. Experiment with the needle position as well.

Here's some good tech:
http://www.4strokes.com/tech/4sjetting.asp

The jets are cheap at rmatvmc and it's $7 shipping on orders <$99. It's cheaper than gas in the truck to go to my local shop.
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Old 01-05-2015, 03:02 PM   #3
afordableperformance
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Altitude

I've been at several altitudes with many different bikes. 8000' will not be too bad, even stock, most newer bikes are lean anyway. 10,000' and above is when it becomes an issue. I have been going to Colorado many years and the rule of thumb with 4 strokes has been go down 10% on the main and call it good, no messing with air/fuel screw or needles. So a 150 main would be replaced with a 135 and that has worked great for us on all our bikes. Some bikes and carbs like more or less and are more sensitive to changes, but overall 10% has been golden for us from 10,000' to 14,000'. There are other tricks that help in a pinch, we had ATV's one year and they liked it better with the cover of the air box removed above the tree line (12,500') but otherwise were OK. Pulling the snorkel of the air box may also help a little, but overall 10% has been fine for a week of trail riding. Hope that helps, I'd try the tricks listed above if it doesn't run well stock and have a 10% smaller main jet on hand just in case, but if you're not over 8,000' you'll probably be better off than you realize. We have brought everything from an XR80 to an XR650L and never had an issue with only swapping the main.
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Old 01-05-2015, 05:52 PM   #4
gnorv
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Joined: Dec 2006
Location: Kansas
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Quote:
Originally Posted by afordableperformance View Post
I've been at several altitudes with many different bikes. 8000' will not be too bad, even stock, most newer bikes are lean anyway. 10,000' and above is when it becomes an issue. I have been going to Colorado many years and the rule of thumb with 4 strokes has been go down 10% on the main and call it good, no messing with air/fuel screw or needles. So a 150 main would be replaced with a 135 and that has worked great for us on all our bikes. Some bikes and carbs like more or less and are more sensitive to changes, but overall 10% has been golden for us from 10,000' to 14,000'. There are other tricks that help in a pinch, we had ATV's one year and they liked it better with the cover of the air box removed above the tree line (12,500') but otherwise were OK. Pulling the snorkel of the air box may also help a little, but overall 10% has been fine for a week of trail riding. Hope that helps, I'd try the tricks listed above if it doesn't run well stock and have a 10% smaller main jet on hand just in case, but if you're not over 8,000' you'll probably be better off than you realize. We have brought everything from an XR80 to an XR650L and never had an issue with only swapping the main.
That is my experience to on my 230L.
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