how to tell if you carb is properly jetted?

[Toyorider]

how can i check if my carb is jetted properly. and are there any basic instruction somewhere to jetting a carb. like which adjustments to mess with first...

[zedicus00]

first and formost a properly set up carb has the slide close all the way. so it shouldnt idle.... second start with the pilot jet and air screw. start with a pilot that should be rich, fire the quad up let it warm up hold it at about 3000 rpm, then turn the air screw until the engine is at its highest RPM. if yur more then 3 turns out yur jets too rich if yur under 1 turn out yur too lean. change jet an staart over. once u get into that range do the main jet. if you play with needles its wise to start the process over. needle thicknes and clip position play parts on how the bike runs fron after 1/4 throttle....

i think i got everything... if i missed sumthing sumone else feel free to add, or correct.

[fireburns99]

Very thourough zedicous. Thats agreat starting place, i don't think i've seen anyone mention a method for jetting that involoves the pilot, and airscrew. But once he gets the pilot then hes going to to need to do plug chops for the main jet.

[Toyorider]

how do i go about adjusting the main jet? the pilot jet instruction were very detailed.

[xcracer416]

go to duncan racings web site they have a dang good jetting instructions there, i think its in the technical link. i jetted mine with their instructions and it was perfect

[Toyorider]

how do i tell what rpms the motor is at?

[beerock]

Originally posted by fireburns99
Very thourough zedicous. Thats agreat starting place, i don't think i've seen anyone mention a method for jetting that involoves the pilot, and airscrew. But once he gets the pilot then hes going to to need to do plug chops for the main jet.

actually the pilot and a/s are separate form the main and needle. pilot is for idle to 1.8 throttle which means you never really use the pilot for power

zedicus that is not true about the slide, the slide is proped up by the idle screw and opens the slide for idle ;)

from duncan:
On many models screw must be screwed in most of the way for proper idle speed. PE models also have a screw/spring that manually raises the slide. On PE models idle screw is approximately 2" below carburetor cap and perpendicular to the slide.


I personally have a radical port job on my 265 R motor and the idle screw will not allow the motor to idle(its very close but not high enough) so i use my throttle cable to adjust the slide.

[zedicus00]

well tru, maybe i should refrase part of that. its best not to let yur quad idle, and have the slide close all the way... its easier to decelerate like this and removes potentially having to run yur quad down if for some reason it bucks you... this is of course a bit of personall preference though...

you can still seize up an engine by having a lean pilot. plus it makes jetting easier if its set up right. the pilot is only used itself for very low throttle but it isnt shut off or disabled completly at high throttle either.

if u want it to idle using the idle screw cut off part of the spring that goes aroud the idle screw.

and radical porting makes jetting... um, fun. also dont forget things like elevation,. temperature, humidity. and yur gas to oil ratio, they all play parts in jetting.

things like too much filter oil on the filter can make it feel like its not jetted right, and air leeks in the engine can have the same effect....