random thought

[4cfed]

this should give you something to think about today, this isnt atech question.. more of just a random thought.....

a atv/dirt bike needs to be rejetted for cold and warm temp changes, due to the cold air being more dense, fuel also becomes more dence when cold, so if air is more dense and fuel is more dence, (expand and contract due to temps) why do machines need bigger jets in winter??

i know to rejet and im not arguing with that fact, just figured id see if anyone could come up with a good answer

 

[lasxgames]

the air becomes dense but allows more air per volume, fluid will become slower moving especially with oil in it, thus more air than gas to motor.

 

[AcidRayn]

i live in NJ, ran 2 strokes for 30 years, thru winter, summer, up in PA mountains, never ever did a re jet for altitude or cold.

not saying that you should not, just sayin, and ive had hodaka, ceezee's, huskies, hondas, yamahas. never had to do it. had a guy i used to ride with, told me i was crazy, after a whole weekend of ice racing on lake george, i pulled new plugs i had put in when we got there, looked just like the ones that came out, which were in there from the fall, at a lower elevation.
maybe im color blind

 

[sheeblast]

the density of air changes greatly compared to gasoline.

lets do this calculation. to make it simple, we are mixing at a 1:1 ratio
at 300K
gas has a density of .694g/cm^3
air has a density of 1.17kg/m^3 (or .00117 g/cm^3)
so at 1:1 ratio, you will have .00117g or air per .694g of fuel
so the ratio of weight of fuel to air is 594
so at 400K
gas has a density of 0.622g/cm^3
air has a density of around .91kg/m^3 (or .00091g/cm^3)
so at 1:1, that is .622g of gas to .00091g of air.
so ratio of weight for fuel to air is 684.

that is a big difference.

read these, about air pressure and density vs temp and elevation
Air - Altitude, Density and Specific Volume
Air - Density and Specific Weight

fuel
Answers.com - How does temperature affect the density of gasoline or petrol

 

[sheeblast]

in the above, that is 100C change, but that is all the data i could find.
but notice how little the density of fuel changes?
only a 10.3% change for fuel where air had a 22.2% change.

 

[Awk08]

in ran my '96 blaster from day 1 to 8 years later, with stock jetting and sold it with the stock piston in it, in weather ranging from 90+ - well below freezing temps, and greatly varying altitudes, prolly a 1000 ft difference from where i live to the top of "awk mountain" and never touched a thing, which is prolly why this worked, it was completely stock, even the oil injection, which prolly had more to do with no rejetting ?????
i firmly believe the more you mod these things the more they are subject to rejetting for temps and altitude

 

[sheeblast]

i firmly believe the more you mod these things the more they are subject to rejetting for temps and altitude

that is so true
the last banshee we had, never changed jets in it after putting the 404 kit in. ran a hard 6 years on it.

running lean normally causes the engine to run hot. so running a tad lean in very cold weather can be masked because the engine can stay cooler.

or if you run it spot on in the cold, running a little rich when it is warm out isn't a bad thing.

 

[Awk08]

i f'in tired of jetting, i'm pullin my motor while it still is running beast, so i dont even get any bright ideas of running it during the winter
i'll run my boys basically stock internals/carb for the winter

 

[xKroniK13x]

I never changed my jets for winter / cooler weather and haven't had a problem... and the change in altitude never effected mine too much either. I know you should, but for the amount I ride in the winter and cold weather (once or twice), it isn't worth it.

 

[4cfed]

Good info guys, rep coming when I get on the computer ( on my phone at work) bbahahahhaa

 

[yzrider]

this is why i'm gonna be runnin a dial a jet after my rebuild this winter, so i can slap the approimate right size jet in and then do all the adjusting and fine tuning from the knob, haha, i am like getting sick sitting here wanting to rebuild, i think theres something wrong with me......... i have the rebuld sickness

 

[Awk08]

i have also considered the dail-a-jet, just for added insurance.
read the details on them, says they only work if a lean condition is present, such as cooler temps, or sudden airleak, sounds like a good insurance policy to me

 

[yzrider]

i have also considered the dail-a-jet, just for added insurance.
read the details on them, says they only work if a lean condition is present, such as cooler temps, or sudden airleak, sounds like a good insurance policy to me

yah, i really like them, so i'm goin for it this year