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View Full Version : High altitude carb adjustments



danny9696
05-18-2009, 08:36 AM
"Hi all I have an 89 force 125 ob that I need to jet for 4500' elevation, can anyone tell me what size jets I need in my top and bottom carbs, the stock ones are as follows; top .101, bottom .0937. I foubd jets to by but am having a hard time figuring out what I should use. I found .092 1500'-3000', .090 3000'-4500', .088 4500-6000 and .086 6000 and up. can anyone shed some light on this for me

Thank you"

galamb
05-18-2009, 12:51 PM
"The jet's you found sound about right (in their ranges) for the bottom jet.

Moving up to 4500 feet would normally result in a jet approx .002 to .003 smaller than the sea level standard. The air is thinner so you want to mix just a touch less gas (in the carb) to get the correct blend.

So on yours I would be looking for the closest jet available to .098 (top) and .090 (bottom). It's not a perfectly exact science.

Alternately, if this is not a permanent move (just taking the boat up for a week(end) etc), if you have a spare prop that is a couple of inches less in pitch than you normally run, that would compensate well enough. The motor wouldn't have to work as hard to turn the (smaller) prop which would mean it wouldn't have to breath as hard to do it...."

danny9696
05-18-2009, 01:45 PM
"Thank you for the info, I called a shop and they told me to put .092 in both, so I split the difference and put .094 in top and .092 in the bottom, do you think that will work"

galamb
05-18-2009, 03:24 PM
No reason it won't work for ya..