Cold weather jetting

[theexception_03]

Hi
Just a general question about jetting for cold wet conditions

I am under the impression that when its cold and damp/raining/foggy then I can run a richer set up compared to when its hot and dry. Considering the elevation I ride at is always less than 1000 feet

Is this correct?

cheers

 

[Jakobi]

Yes and no.

Consider that jetting is trying to achieve a consistent and optimal air fuel ratio. More air requires more fuel. Less air less fuel. When we say air, we're actually interested in the oxygen as thats what combusts. Humidity means higher water content in the air = less oxygen = less fuel required. Hot air isn't as dense = less air = less fuel required. When you go to alititude the air is thinner = less air = less fuel required. Then the catch is that they can both be in effect together. Higher altitude = thinner air = leaner jetting, but it may also be much colder = denser air = richer jetting. In this case they may balance out.

For weekend warriors like ourselves the best approach is just to ride and if the bike shows characteristics of being a bit under powered and flat on a cold day stop and richen it up a bit. If its a hot humid day and its blubbery lean it off a bit. Generally you'll get away with just making a few tweaks on the air screw and it'll be near enough.