cold weather.....richer or leaner?

[sica]

i rode my 400ex today for the first time in 3 weeks and today was the first time it has been cold(35degrees) i have a dmc full exhaust with k&n filter with a 42 pilot and 152 main,stock needle on the 4th position.....it ran like crap...it sputtered and backfired alot......my question is does the mixture get richer or leaner in the cold weather and what do i need to do???
thanks,

[300exOH]

you need to richen up in the winter because the air is more dense(more oxygen). Backfiring is usually a result of a lean condition.

[Steve-o 400EX]

You need to make of for more oxygen with fuel. The air is denser so you need to mix the fuel heavier. usually this only requires going up a size or 2.;)

[cals400ex]

if it is backfiring on deceleration, you might just have the fuel skrew turned in too far. 2.5 turns out should be just fine. you might be a tad lean on the main too. you could also try going up one or two sizes on the main, however, this shouldn't have anything to do with the backfiring. old gas or a dirty carb may give problems too.

[skemp]

Sorry guys, but colder air is more dense, requiring more fuel. To make up for more air, you add more fuel. 1 or 2 sizes will usually do it.

[2004TRX450R]

Originally posted by 300exOH
you need to richen up in the winter because the air is thinner(less oxygen). Backfiring is usually a result of a lean condition.

Yes you need to richen it but because the air is more dense not thinner and has more oxygen not less. If it is lean that means it is getting to much air and needs more fuel. How does less air mean you need more fuel?

[sica]

well now i am more confused...there are two separate opinions on here..

[Aceman]

You need to richen it up. Ever notice how tires look almost flat in really cold weather? It is denser. Problem solved!

[ReconRider25]

colder air is more dense making it lean, do to more air being crammed into the carb, so you have to richen up the mixture to compensate for the higher amount of air.;)

[JOEX]

Colder air = more dense, which means more oxygen. The same amount of 'air' is going through the motor it just has more oxygen in it. Youy will want to run larger jets for the colder weather.

When you go up in elevation the air is thinner, less dense, having less oxygen and you will want to run smaller jets.

Joe

[DamageInc]

Originally posted by sica
well now i am more confused...there are two separate opinions on here..

Don't be confused; cold air is more dense, so you need more fuel. FACT, not opinion!

colder air ,more oxygen, richer jet.


how bout deleting the bad posts?

don't want to give people the wrong info

[zephead400ex]

SICA: you will need more fuel. Bigger jets = more fuel. Also you will want to check your fuel mixture screw.

Dont be confused man...jetting is a mug!

peace

[300exOH]

Edited my post. I meant to say the air was more dense and had more oxygen but you do still want to richen up in the winter. My mistake. Sorry about the confusion. I don't know what I was thinking. Thanks for correcting me guys.

[jcs327]

Yes, the air is more dense in the winter. That is why airplanes take less runway in the winter than summer. The air is more dense, so the wing gets more lift. BUT THER IS NOT AN INCREASE IN OXYGEN. normal air is 21% O2. It does not change with temp.
Thats coming from both a private pilot & a paramedic who owns a quad, but that's JMO.

[DamageInc]

Originally posted by jcs327
Yes, the air is more dense in the winter. That is why airplanes take less runway in the winter than summer. The air is more dense, so the wing gets more lift. BUT THER IS NOT AN INCREASE IN OXYGEN. normal air is 21% O2. It does not change with temp.
Thats coming from both a private pilot & a paramedic who owns a quad, but that's JMO.

There is an increase in the amount of oxygen by volume. The percentage of oxygen in relation to the other gases in the air remains the same, but the amount of oxygen in a cubic foot of air does increase.

[jcs327]

I see. So there is actually a larger volume flowing through the carb, thus needing more fuel.

[DamageInc]

Originally posted by jcs327
I see. So there is actually a larger volume flowing through the carb, thus needing more fuel.

Not really, the volume of air is still the same, but the amount of air within that volume is greater (it's more dense). Not just the amount of oxygen, but also the amount of nitrogen, CO2, etc. There is more oxygen in cold air than warm, but also more of every gas, so the percentage is pretty much the same, but there is more of it in that given volume.
The reason a turbo gives more power, even at altitude in thinner air, is that it keeps the air dense all of the time. The cylinder can only hold a certain volume on every stroke (i.e. 400cc), but if you can pack a higher density into that space, you can make more power.

[RiPPiNiTuP7]

very simple:

temp down=jet up
temp up=jet down

just remember..do the opposite of the weather.

[sica]

thanks guys this helps me now