Does humidity affect jetting?

[wilkin250r]

I know elevation and tempurature affect jetting. Does humidity affect jetting? I don't see how it would...

[UglyMotha™]

i would think that it does cause when it's humid out isn't the air more denser or vice versa or am i just talking out my butt here :confused:

[wilkin250r]

Originally posted by UglyMotha™
i would think that it does cause when it's humid out isn't the air more denser or vice versa or am i just talking out my butt here :confused:

Thanks for the support anyways... :rolleyes:

j/k

[UglyMotha™]

i tried

Id' have to say yes. The air is thicker when it's humid meaning more dense. Probably have to drop down on the main to compensate. Just like you have to go up on yoru main in the winter because of the air being less dense....:cool:

Or maybe I'm talkin out ma butt too....:ermm:

[F-16Guy]

Humidity does affect jetting. Moisture displaces air, so you'll have to lean out your mixture a little.

Originally posted by wilkin250r
Does humidity affect jetting? I don't see how it would...
absolutely

[wilkin250r]

Originally posted by Rico
Id' have to say yes. The air is thicker when it's humid meaning more dense. Probably have to drop down on the main to compensate. Just like you have to go up on yoru main in the winter because of the air being less dense....:cool:

Or maybe I'm talkin out ma butt too....:ermm:

But cold air is MORE dense than warm air...:confused:

Not only that, when the air is more dense, wouldn't you go UP on the jet, because with greater density, you have more oxygen, so you need more fuel?

[FrankMX]

Keep in mind that the best combustion is around 14,7 part of air for 1 part of gaz. If the air contain more water, you need more air too keep this ratio. During the winter the air is more dry and contain more oxygen.... you need more gaz.

For theses reasons i run a little bigger main jet to play in the snow :p and the stock main jet during the summer.

[Colby@C&DRacing]

Really good answers guys. :)

[NoWingNoPrayer]

This is all true but i would have to say unless you are in fog that yo can cut with a knife, i dont see how it could hurt your performance to where you would need to fix it.

i have had my 400s airfilter considerably damp before and i never noticed a difference.

I could be wrong.

[JOEX]

I find this very interesting.... we need some more input on this for fine tuning... :)

Joe

[cals400ex]

the humidity should make a difference on jetting. go to www.hondaex.com on the tech page there are a few things on jetting and this may help clear things up.

[FrankMX]

The ratio of 14,7:1 is a theoretical value.... you will probably obtain more performance with a 13:1 air/gaz ratio... but I don't why.... :rolleyes:

Your filter will probably absorb a part of this humidity.....

If you don't believe me.... just buy an old carburator car and run it during a cold rainy day.... I'm pretty shure that you will have some problems with the idle........ perhaps that the car will stop... :p

New EFI engines don't have this problem because we have an O2 sensor, a coolant sensor, a mass air flow sensor...... and more...

The computer calculate how much gaz the engine needs with theses sensors data... to have the best performance

I know that because i'm trying to build a fuel injection system for my EX.... :eek:

Originally posted by NoWingNoPrayer
This is all true but i would have to say unless you are in fog that yo can cut with a knife
good statement ,,,
"fix " probably not ..in most cases
...."tweek" ..a lil most likely

[SR71]

Increase in humidity will decrease the mass flow of dry air into the carb due to the increase in specific volume of air. A quick look at a psychrometric chart indicates the following changes in airflow for the following changes in humidity:

80 deg F/ 40%RH to 80 Deg F/80%RH = 1.45% less dry air

Extreme change:
90 deg F/40%RH to 90 Deg F/80%RH = 2.12% less dry air

One more example:
70 deg F/50%RH to 90 deg F/80%RH = 6.66% less dry air

My initial thought without much time, if jetted properly (not too lean or rich) at standard conditions 80 deg F/60%RH, you won't notice much of a change. Winter to summer is a different story.

Just food for thought.

[UglyMotha™]

I have no clue what you just said :confused:

Originally posted by SR71
you won't notice much of a change

Just food for thought.
I THINK I said that in my second post :confused:

[SR71]

Mr. 2R's, while I can appreciate your comments, my post was intended for those wishing for a bit more information, such as JOEX.

MR....?

[SR71]

I'm trying to be polite.

[UglyMotha™]

Originally posted by "2-R's Rider"
MR....?



2-r's a Mrs.......:confused:



:D

Originally posted by UglyMotha™
I have no clue what you just said :confused:

[UglyMotha™]

:macho

[wilkin250r]

Originally posted by SR71
Increase in humidity will decrease the mass flow of dry air into the carb due to the increase in specific volume of air. A quick look at a psychrometric chart indicates the following changes in airflow for the following changes in humidity:

80 deg F/ 40%RH to 80 Deg F/80%RH = 1.45% less dry air

Extreme change:
90 deg F/40%RH to 90 Deg F/80%RH = 2.12% less dry air

One more example:
70 deg F/50%RH to 90 deg F/80%RH = 6.66% less dry air

My initial thought without much time, if jetted properly (not too lean or rich) at standard conditions 80 deg F/60%RH, you won't notice much of a change. Winter to summer is a different story.

Just food for thought.

Where do you get your information? I'm not questioning it's accuracy, I'm just interested because it is so detailed and specific.

[F-16Guy]

Originally posted by wilkin250r
Where do you get your information? I'm not questioning it's accuracy, I'm just interested because it is so detailed and specific.
What, you don't have a psychrometric chart layin around somewhere? :blah:

[wilkin250r]

Originally posted by F-16Guy
What, you don't have a psychrometric chart layin around somewhere? :blah:

Well, my calculations were a little different. Then again, mine were based on phase changes of ionic nitrogen gases due to laser photonic excitation in a Faraday cage, so I didn't know if they were related...

[JOEX]

SR71....
Thanks for the added info;) I don't fully comprehend it yet, gotta read it a few more times:p

Joe

[ATVer14]

Humidity isn't great for power, but it does wonders for cooling!

[bmw500hp]

Originally posted by cals400ex
the humidity should make a difference on jetting. go to www.hondaex.com on the tech page there are a few things on jetting and this may help clear things up.

it is difficult to navigate that site...did get to the post where one of "there" got ripped off on ebay buying a camera...then he found by coincidence it was the site owner...lol...think I hang out here on exriders.....:eek2:

[SR71]

I'm not an internet expert, but you can probably find a Psychrometric chart out there somewhere.

One could oversimplify slightly and just look at the % changes in specific volume and say this is how much your fuel to air ratio would change under the stated conditions.

Example : 80 deg F/ 40%RH to 80 Deg F/80%RH = 1.45% less dry air
So if your were jetted "perfectly" at 80 deg F and 40% relative humidity, then at 80 deg F and 80% relative humidity your quad will be running 1.45% rich.

F-16Guy, Unfortunately, I do have charts like this "layin around" my office. It's really sad. I try not to think about it much.

[F-16Guy]

You work at Skunk Works?

[wilkin250r]

SR71, what type of work do you do? Will humidity affect other aspects of engine performance, by affecting the specific wieght of air? This can have an effect on the scavenging and camshaft characteristics?

I'm thinking that 1.5% more or less oxygen in a given volume will have little effect on jetting.

Do you have any info (or even and educated guess) on the differences 1000ft change in altitude would make on % of oxygen in a given volume?

[SR71]

Wilkin250r,
The biggest impact humidity will have is on your fuel/air ratio. In theory, one could make a stretch of an argument that cams could be tailored to different ambient conditions, but obviously it would not be worth the time or money for the minimal gains one could get.

1.5% change in available oxygen could be close to 1 size different jet. But like I said, if you are jetted for 80 deg/60%RH, you would only see half of that change in specific volume, in which no jet change is required.

All else being held constant, a 1000 ft elevation change results in about a 3.6% change in air density. You can look at three different tables and get three different answers because some use typical changes in temp and or humidity with respect to changes in elevation. The 3.6% is based only on elevation change, which is simply driven by the change in barametric pressure.

[wilkin250r]

Do you really think that 1.5% more or less oxygen could make a difference in jet size?

I figure that a 15 degree temp change would make more than 1.5% difference in available oxygen, but I don't know anybody that changes jets in the morning, afternoon, and evening because of the tempurature change...

[SR71]

Yes, I think a 1.5% change in oxygen could justify a jet change, but may not necessitate one. It depends on your initial stoichiometric ratios, the direction of the change in stoichiometric ratios, and your motivations for optimization.

You are correct, a 15-degree change in temperature does have a greater effect on the specific volume of air (3 to 4%) than the typical daily changes in humidity. And I agree with you that most people don't change their jets three times a day. Most people don't really even know what jets are, never change them, and still manage to have a lot of fun. However, if the average daily temperature changes 15 degrees, there are many people that do change their jets. As with the humidity discussion above, it all depends on your initial stoichiometric ratio, the direction of change, and your motivations for optimization.