Jetting changes for temperature

[JimAC]

I rode this weekend in 45 -50 degree weather and ran a lot better than when it was 80-85 during the summer. Is there any info or formula for jet size and temp ? If it runs better in the cold it must be rich when it's warm right ?

I have stock carbs with 28.5 and 300 and pro design cleaner with k n power lid

Water temp was 150-160

I am talking about the upper half of the throttle

 

Thanks for any help

Jim

[black sunshine]

I rode this weekend in 45 -50 degree weather and ran a lot better than when it was 80-85 during the summer. Is there any info or formula for jet size and temp ? If it runs better in the cold it must be rich when it's warm right ?

I have stock carbs with 28.5 and 300 and pro design cleaner with k n power lid

Water temp was 150-160

I am talking about the upper half of the throttle

 

Thanks for any help

Jim

 

I wan't to say that it's every 25-30 deg F for a main change. You could PM daogejr 'cause I'm pretty sure he posted it up. It will run better when lean, but the problem is I don't think you have a baseline to go from. You may have been jetted right for 85F and it is running lean right now. If you knew your jetting was spot on in the summer then you could bump up a size or two right now and know you are ok.

[xXBlessedWithDeathXx]

The colder the leaner it will run. take caution, you dont want to blow your ride up.

[BellicoseBanshee]

Click HERE for full article posted by sredish...

 

Altitude, Humidy, and Air Temperature

 

Once the jetting is set and the bike is running good, there are many factors that will change the performane of the engine. Altitude, air temperature, and humidity are big factors that will affect how an engine will run. Air density increases as air gets colder. This means that there are more oxygen molecules in the same space when the air is cold. When the temerature drops, the engine will run leaner and more fule will have to be added to compensate. When the air temerature gets warmer, the engine will run richer and less fuel will be needed. An engine that is jetted at 32 degrees may run poorly when the temperature reaches 90 degrees.

 

Altitude affects jetting since there are less air molecules as altitude increases. A bike that runs good at sea level will run rich at 10,000 ft due to the thinner air.

 

Humidy is how much moister is in the air. As humidy increases, jetting will be richer. A bike that runs fins in the mornings dry air may run rich as the day goes on and the humidity increases.

 

Correction factors are sometimes used to find the correct carburetor settings for changing temperatures and altitudes. The chart in fig 8, shows a typical correction factor chart. To use this chart, jet the carburetor and write down the pilot and main jet sizes. Determine the correct air temperature and follow the chart over to the right until the correct elevation is found. Move straight down from this point until the correct coreection factor is found. Using fig 8 as an example, the air temperature is 95 degrees and the altitude is 3200 ft. The correction factor will be 0.92. To find out the correction main and pilot jets, multiple the correction factor and each jet size. A main jet size of 300 would be multiplied by 0.92 and then that number can be rounded up to the next main size. For instance, 300 x .92 would be 276, so a 280 could be used. A pilot jet size of 30 would be multiplied by 0.92 which comes to 27.6, so the pilot jet size would be a 27.5.