How does air temp effect jetting?

[Chris S.]

The reason I ask is that I had put a 500 stroker motor in my 400EX and it was in my basement and I had it running perfect. Idled great, reved smooth with little backfiring when deceling. I finally got it outside to day and it was backfiring and hissing through the airbox and occassionaly it would misfire. It was about 45 degrees outside and it was about 70 degrees in my basement. All other settings were the same. Is it possiable that I need to rejet for the winter cold air and if so do I go smaller or bigger?

[zeppelin]

when it is colder the air bcomes denser and it wil need more gas, but you shouldnt notice the big differces you have just from temps. before you start playing around jets try adjusting your fuel screw, and make sure your air filter and carb are clean

[bwamos]

Aye, it will make a minute dofference on a 4-stroke. More noticable on 2-strokes.

Cold air is denser so you have more oxygen per cubic inch wich will make you run a little leaner.

Humidity reduces the amount of oxygen per cubic inch so makes you run a little richer.

But on a 4-stroke it shouldn't make much of a difference.

If your "hissing" thought the carb and filter, it sounds like your cam timing is too early and you're intake is opening up before the exhaust gasses have escaped from the cylinder.

[JOEX]

Doesn't it make a difference when the motor is sitting still and being reved vs. actually riding and putting a load on the motor?