Cold weather jetting??

[Pa Dirt Eater]

Now that winter is on the way, I was wondering if you go up or down in main jet size for the cold temps? also will the cold temps affect the pilot jet??? Any help would be greatly appreciated.

[John451]

leave it. Cold weather doesnt do anything to it except for make it take longer to warm up. Once it's warmed up it'll run the same. The only thing you change is the rotation on the mixture screw IF you notice a diffeerence in the rev pattern.

[Pa Dirt Eater]

I wish cold weather did not change anything. My son races a 50cc DRR quad and when the temp drops below 58 degrees it stalls when he attempts to go wide open. Runs awesome above 58 degrees all year long.... but it's starting to get cold. I know that the main jet needs to be changed then, just don't know if it needs to be a jet size larger or smaller??

[GPracer2500]

cold air = denser air = more fuel needed

[John451]

Yes, that's what the mixture screw is for, if you adjust that you're set.

[Toadz400]

Originally posted by John451
leave it. Cold weather doesnt do anything to it except for make it take longer to warm up. Once it's warmed up it'll run the same. The only thing you change is the rotation on the mixture screw IF you notice a diffeerence in the rev pattern.

Cold weather makes a HUGE difference in jetting. Telling him to leave it is not smart.

How cold does it get? Back in WI I would have to go up at least one main and pilot jet size and drop the needle clip at least one position during the winter. I adjust the fuel screw almost every time I ride because with changing temperatures it's going to be different. The fuel screw is more of a fine tune adjustment.

[John451]

Well if it's running differently then it does need to be messed with haha, but one of my friend's was trying to tell me (a mechanic of 8 years) that if you don't change the main jet the motor will blow. And i asked one of my friend's that's been workrin on them for over 40 years and he said it doesn't do anyting like that.

[Toadz400]

Originally posted by John451
Well if it's running differently then it does need to be messed with haha, but one of my friend's was trying to tell me (a mechanic of 8 years) that if you don't change the main jet the motor will blow. And i asked one of my friend's that's been workrin on them for over 40 years and he said it doesn't do anyting like that.

Not changing your jetting during the winter if you experience drastic temperature change increases the chances of a lot of bad things. Air is denser when it is cold. This means there is more oxygen per cubic whatever you want to measure it in. Your engine will run leaner and hotter risking pre-detonation if you do not add more fuel. This can and will lead to engine failure.

[Pa Dirt Eater]

Here in PA the summer temps range from 90-95 degrees and in the winter 15-20 degrees. It would appear that I need to go up a main jet size as the winter approaches. Here's a good web site to check out about jetting : http://g-forcepowersports.com/catubydura.html Thanks for all the opinions on the subject. If you thought that no adjustments were needed please check out this jetting guide by Duncan racing at the above listed link.

I never change jetting for air temp and where I am in 1 year it goes from up to almost 100f to -30f and the engines are fine. Plugs dont even read lean/white. To have a engine running at its best a carb needs to be adj or jets changed every 20 degrees gain or loss in air temp. Your engine also make more power when it's colder out from sucking more air in as long as your fuel/air ratio is good. A lot of carb quads have a hard time starting in winter if you dont up the pilot.

[Toadz400]

Originally posted by spastic450
I never change jetting for air temp and where I am in 1 year it goes from up to almost 100f to -30f and the engines are fine. Plugs dont even read lean/white. To have a engine running at its best a carb needs to be adj or jets changed every 20 degrees gain or loss in air temp. Your engine also make more power when it's colder out from sucking more air in as long as your fuel/air ratio is good. A lot of carb quads have a hard time starting in winter if you dont up the pilot.

You just contradicted yourself there buddy.

When I was in WI (temps from 100 to -50) I always rejetted whenever the seasons changed. There's usually a good 20-30 degree difference between each season.

Also, two-strokes are much more touchy when it comes to temperature change. I believe it's for every 10 degrees you should rejet a two-stroke for optimum performance and every 20 degrees for a four-stroke.