High Humidity and Temp Jetting help

[vincent1209]

Can someone please help me with my assumption about jetting. I am fairly technically challenged in this area. I have an 06 yz450 with all stock jetting and live in the tampa, florida area where we have real high humidity and of course high temps. I have read that the bike will run rich since there is less oxygen in the air from the humidity. So my question is - is my assumption correct? Can I just lean out the jetting a little by raising my needle clip position and adjusting the air pilot screw? I am looking for the jetting for dummies 101 tips here.

My symptoms from the bike are a slight popping when backing off the throttle... not back firing just a pop - pop sound. Thanks!!

[99raptor]

For sure I'm no expert but I thought popping on de-celleration was a lean condition,and hi humidity causes leaning out of the mixture.

[CRFThumper]

The popping you are talking about can be caused by a lot of things.More often than not it is related to the pilot circuit,so if you turn you're fuel screw

out a 1/4 turn at a time it should go away!Keep in mind that if to have to go more than about 2 1/2 out you will need to go up on the pilot! The needle does not come into play until about a 1/4 throttle. YES there is some overlap

but generally speaking the idle our pilot circuit is to blame!

[bg10459]

For sure I'm no expert but I thought popping on de-celleration was a lean condition,and hi humidity causes leaning out of the mixture.

High humidity/temperature does not cause a lean condition, it REQUIRES a leaner mixture. If there is less oxygen in the air because high humidity has displaced it, because high temp air is less dense or because high altitude air is less dense, the same mixture will be too rich. Generally, you need to richen your mixture for cold, dry, low altitude conditions and lean it for hot, humid, high altitude conditions.

[99raptor]

The original poster was from Florida,,,hardly a hi altitude state

[Ga426owner]

Can someone please help me with my assumption about jetting. I am fairly technically challenged in this area. I have an 06 yz450 with all stock jetting and live in the tampa, florida area where we have real high humidity and of course high temps. I have read that the bike will run rich since there is less oxygen in the air from the humidity. So my question is - is my assumption correct? Can I just lean out the jetting a little by raising my needle clip position and adjusting the air pilot screw? I am looking for the jetting for dummies 101 tips here.

My symptoms from the bike are a slight popping when backing off the throttle... not back firing just a pop - pop sound. Thanks!!

Stock jetting is way to lean:

go up on your pilot jet to a 45 or 48

go up to a 165 mj or 168

I am just north of you at 900ft to 1800ft - I am at 48pj/168mj - stock clip position and no popping and great power :thumbsup

[Baron Von Beard]

High humidity requires slightly leaner jetting due to the less dense air. Same goes for high temps.

For sea level with high temps and high humidity, I would suggest a 45 pilot, 165-168 main and needle on the 4th (stock) clip position. Make these changes and then set the fuel screw as per Eddie's "Sticky" at the top of the jetting forum.

[vincent1209]

Thanks everyone for the input. The stock main is a 165 on the 06yz450 and the stock pilot is 42. I will try to lean it out like bg10459 advised. I guess I got confused because the yz manual says to go higher for rich and lower for lean but I guess it depends on your reference. Is it saying if your mixture is rich go high or if your want to make it rich go high?? I guess it is the mixture...

Does anyone strongly suggest I don't touch the needle clip position because the stock bike didn't come with a main jet that would work for me ( 172 and 178 ). Honestly, it seems like the easiest option to lean out the broadest part of the throttle position... so I figured adjust the pilot and raise the clip? Any thoughts???

[grayracer513]

High humidity/temperature does not cause a lean condition, it REQUIRES a leaner mixture. If there is less oxygen in the air because high humidity has displaced it, because high temp air is less dense or because high altitude air is less dense, the same mixture will be too rich. Generally, you need to richen your mixture for cold, dry, low altitude conditions and lean it for hot, humid, high altitude conditions.

High humidity requires slightly leaner jetting due to the less dense air. Same goes for high temps.

For sea level with high temps and high humidity, I would suggest a 45 pilot, 165-168 main and needle on the 4th (stock) clip position. Make these changes and then set the fuel screw as per Eddie's "Sticky" at the top of the jetting forum.

These two are 100% correct (to a 1.3% tolerance). I run a 45/165/4th clip setup in Southern SoCal at altitudes ranging from 2000 to 3500 so far, temps 70-95, humidity running the gamut. It's not always spot on, but it always runs good, and pops very little if at all.

My experience has been that humidity is less of a factor than temps are, and altitude has the greatest effect overall, but what these guys have said is accurate.

Decel popping is something of a YZF trademark. Some of it is fairly normal, and as long as there are no performance issues apart from it, you shouldn't let it bother you at all. It is true, though, that the '06 was built somewhat lean.

When troubleshooting a decel pop, though, always check the joints in the exhaust for air leaks before you go dumping fuel into the engine to get rid of it. If it's really caused by a leak, your bike will be way over rich by the time it stops popping, if it ever does.