what size jets do i need

[jasonex]

i was wondering what size jet i need for my 07 trx 400ex?
it has a YOSHIMURA RS3 slip on with no spark arrester and a K&N air filter with no air box cover.


thanks

:D

[ohsobad_chevy]

start with:

152 main
42 pilot
3rd needle position
2.5 turns out on the screw

Should get you close, then you can fine tune it.

[leasureryan]

you need the size that makes it run right.


in other words....there are way to many differant jetting specs, conditions, mods, elevation, temp, etc, to tell you which you should be running. It's a matter of test and tune

[Honda#4]

Theres not an adjustable needle on his quad. I'd start at a 155 main.

[rideracelivemx7]

ha it really doesnt matter what size you start off with,(with a real jet kit!) others will argue against me but i had the completely stock quad at the time just with the SA out and i did a 42 pilot and a 170 main on a stock engine and it ran like a clock after i dialed in the air screw. so you can probly ram fuel down its throat if you do a real jet kit and needle like i did. fmf, worked great and fantastic craftsmanship. plug was a nice running color too witht he 170. im running look at my sig and im still running the same jets. could go up a few sizes...

[BamBam730]

Dont know if this will help but I found it on the internet.
http://www.powroll.com/tech_specs_jetting.htm
JETTING GUIDELINES


--------------------------------------------------------------------------------

These jetting specifications are designed as a rule of thumb. They are in no way absolute. Variations in air density, specific gravity of fuel, altitude and other engine modifications play a large part in jetting. It is the responsibility of the owner to determine proper jetting for their engine.

HOW TO JET - THE BASICS
Plug reading doesn’t work. Revving the engine while it’s sitting in the garage doesn’t work. Other than Dyno testing, the steps below are the only way you can consistently jet your engine.

1. Find a gentle slope that you can ride in 2nd or 3rd gear. Look for something that will put a decent load on the engine. This will be your tuning test area.
2. Make the recommended jetting changes. Always start rich and work leaner.
3. A basic outline of which jet is active at a particular throttle setting:
Pilot Jet = 0 to 1/4 throttle. Needle = 1/4 to 3/4 throttle. Main Jet = 3/4 to Full Throttle.
● Changing the Main Jet size won’t affect how your engine idles or runs at 1/4 throttle.
● Engine RPM isn’t what determines which jet is active - only throttle position does this.
4. Start and warm up the engine, then ride your ‘test hill’. Any point where you feel the engine stumble or hesitate indicates a rich condition. Note the throttle position and modify the corresponding jet (1/4 to 1/2 throttle = leaner needle. 3/4 throttle or more = leaner main jet).
5. Only change jetting by 1 step at a time, and 1 circuit at a time (don’t change needle and main at the same time). Re-check after every change.
6. Once the engine runs smoothly throughout, you’re jetted!


If you ever notice an abrupt change loss of power, or engine sounds changes, shut it down.

[leasureryan]

Originally posted by rideracelivemx7
ha it really doesnt matter what size you start off with,(with a real jet kit!) others will argue against me but i had the completely stock quad at the time just with the SA out and i did a 42 pilot and a 170 main on a stock engine and it ran like a clock after i dialed in the air screw. so you can probly ram fuel down its throat if you do a real jet kit and needle like i did. fmf, worked great and fantastic craftsmanship. plug was a nice running color too witht he 170. im running look at my sig and im still running the same jets. could go up a few sizes...

LOL....what is a "REAL" jet kit....lol. Are there fake ones???
if it doesn't matter what size jet you use.... why doesn't everyone just toss random jet sizes into thier carbs? That statement couldn't be further from the truth! And honestly...I am running higher jetting than you...and have an internaly stock motor. You are most likely running lean as all get out

Actualy...jet kits are a waste of money....UNLESS you are just buying one to get the adjustable needle....otherwise....REAL Kehin jets are $4.95 down at any local cycle shop. They are more accurate, and don't give you funky numbers to try and go by. Just because your quad ran with a 170 main...doesn't mean it was the right jet for it. Ever hear the expression....rich is a bbiittcchh.....lean is mean. Jet kits don't even normaly come with pilot jets...which is a must. And half the time, they aren't even close to the actual size you need. They size thier jet kits in catagories...stage 1, stage 2, etc. If there were only 3 places quads ran, and 3 types of mods, with 3 types of weather conditions, and 3 types of everything else....then, and only then could I ever justify grouping quad jetting into 3 stages.

[jasonex]

thanks:D :D

[jasonex]

when i rejet it do i need to take off all the front plastic?