Jetting Baseline

[Architects]

I Have always been confused when it comes to jetting. Im going to be geting exhaust pretty soon and would like to figure out what all I need to get jetted correctly.

- Nmotion pipe.
- No airbox lid.
- Unsure of elevation


- Main jet size? Id guess about a 165-175ish
- Will my stock pilot jet work or am I going to need to bump that up? If so what s
size pilot jet?
- A/f screw how many turns out?
- Needle on what clip?
- Will the stock needle work

If someone could give me some baseline recomendations.


Help a carb newbie out. Thanks in advance

[bradley300]

jetting can be a real pain in the *****. your most sure fire baseline is the stock jetting for the simple reason that you do know the most about it, it's lean. what i do is order 2 pilots richer,and from 1 bigger main than stock to the biggest main everyone says you might need. the needle should probaby be all right, but if you find it runs best on the very top or very bottom notch, order the enxt size (next size richer if its on the bottom, next leaner if the clip is all the way at the top)

i have heard a trick for the air screw is to adjust it until the quad idles the fastest. this should give you a perfect a/f ratio

for the other circuts, do one circut at a time (idle-1/4 throttle for pilot, 1/4-3/4 throttle for needle and 3/4 to full thottle for main) and go up 1 size at a time. checking the sparkplug each time.each time you shut down the quad, keep your thumb at your current circut's position so you dont get a mixxed reading. (you need a nice chocolate brown color, probably take a few spark plugs with you) onc you have got the right color for the pilot, tune the needle, then the main.

[Architects]

thanks anyone got any other advice

[krt400ex]

what is ur stock main jet and pilot jet???

[Architects]

Stock is 118 main and 48 pilot.
I think im going to try

- Hrc needle
-175-185 main
-50 pilot
-Afs 2-2.5 turns

[GPracer2500]

That sounds like a good place to start.

[04TRX400EX]

My knowledge mostly pertains to 400EX's, but an R should be close. If you are running no air box lid, you will definitely need to go pretty big on the main jet. I wasn't aware that stock was a 118 main :eek2: that's really small compared to a 400EX (stock is 148). I don't think you will have to go up all the way to a 175-185. I would say to try something in the 145-155 range. I would recommend lowering the needle clip position down so that it richens up the fuel mixture, and take about 2 turns out of the air/fuel screw to again richen up the settings. When jetting, always get your main jet set first. You have to be right there to establish a proper baseline for tuning the rest of the carb. Check your spark plug color to get an idea of how rich or lean you are and feel how it responds at 1/2-full throttle. If it feels like it is going to crap out on you, you are lean, where if it bogs down it is probably too rich. The plug color is an easy check though. Once you get your main jet squared away, you'll probably notice you are hesitant on the 0-1/4 throttle area, which is needle and screw settings. I would NOT recommend changing your pilot jet unless you get into the internals of the engine. Usually the stock pilot jet is perfectly acceptable for minor engine mods like removing the lid or adding a pipe and filter. Hope this helps :)

[krt400ex]

Originally posted by Architects
Stock is 118 main and 48 pilot.
I think im going to try

- Hrc needle
-175-185 main
-50 pilot
-Afs 2-2.5 turns


is that 118 a typo??? i would have thought that the 450r main would be bigger than the 400ex. any way. u sound like u r on the right track. try it and see how it works, then let us know

[GPracer2500]

118 is no typo. The 450r in showroom stock condition is extremely plugged up. Taking the airbox lid off makes a huge difference on the 450r--far more dramatic than the 400ex.

You can't really draw many conculusions on jetting the 450r based on experience with the 400ex and stock jetting specs. It's sort of apples to oranges.

My XR650R came with a 125 main jet! It actually had a restricter plate in the intake manifold so it would run with that small of a main jet. There's an HRC manifold that doesn't have the restrictor.

Here's the stock restricted one :ermm: :

http://www.xr650r.net/smallold_manifold.jpg

[krt400ex]

Originally posted by GPracer2500
118 is no typo. The 450r in showroom stock condition is extremely plugged up. Taking the airbox lid off makes a huge difference on the 450r--far more dramatic than the 400ex.

You can't really draw many conculusions on jetting the 450r based on experience with the 400ex and stock jetting specs. It's sort of apples to oranges.

My XR650R came with a 125 main jet! It actually had a restricter plate in the intake manifold so it would run with that small of a main jet. There's an HRC manifold that doesn't have the restrictor.

Here's the stock restricted one :ermm: :

http://www.xr650r.net/smallold_manifold.jpg


does the 450r have a restrictor plate??? just curious

[GPracer2500]

Originally posted by krt400ex
does the 450r have a restrictor plate??? just curious

No--not like that anyway. The main restriction on the 450r is the inlet into the airbox. That's why the 04/05 HRC lid is all opened up and the 06 HRC settup is intended to be run without any lid at all.