altitude

[yfz&shee]

what jetting to run around 5000 feet, I have 270 main, 27.5 pilot a/f screw out 1 1/2 I talked to some guys at cascade today and they told me that when you get up this high (I'm from missouri in colorado currently) that you loose compresion. I've never heard this before I have a K&N and t-6s any ideas how to make this puppy run up here? it runs like shit now. Chris from cascade said that at 5000 ft. i'd probly have between 75 and 80 pounds of compresion and under 1000 ft i should have 120 pounds stock.......... thanks for any help i get in advance

[AKheathen]

what jetting to run around 5000 feet, I have 270 main, 27.5 pilot a/f screw out 1 1/2 I talked to some guys at cascade today and they told me that when you get up this high (I'm from missouri in colorado currently) that you loose compresion. I've never heard this before I have a K&N and t-6s any ideas how to make this puppy run up here? it runs like shit now. Chris from cascade said that at 5000 ft. i'd probly have between 75 and 80 pounds of compresion and under 1000 ft i should have 120 pounds stock.......... thanks for any help i get in advance

it's not so much that you loose compression, as that the air is thinner, and the fuel atomises easier, having less oxygen in the mix. you will loose some power, but you need to jet for it. the fuel that you buy up there will varry on how it atomizes, so check your plugs to see which way to go. generally, you go leaner, so if the plugs are pretty black, do so. if you plugs are white or lighter than chocolate brown, go richer. when it starts to run better at wot, do a proper plug chop to tell you where the jets should be. then adjust your airscrews and, if needed, the needles. the loss of compression will loose you a little power, but it'll stillo run good when jetted right.