Maintenance & Technical > KX500 Original

jetting info from the pipe

<< < (2/2)

BigGreenMachine:
I think the EGT sensor is the way to go. That or a dyno.

FuriouSly:

--- Quote --- I did notice a guy with a kx450 that had a sensor welded into his pipe with a wire going to a computer on his handlebars. he said it was for jetting. what kind of info could you get from that type of sensor. temp? and at what rpm the temp was at. from there can you tune the needle,pilot,main....js
--- End quote ---

I use an O2 sensor setup for all my 4 strokes (quads and bikes) to get them jetted correctly.  Basically an O2 sensor that you weld the mount into the head pipe about 12"-18" from exhaust port and thread it in with some anti-seize.  This sensor is powered by 12vdc to heat the element to operating temp for more consistent readings rather than having engine exhaust gases doing it (my 4S all have electric start with batteries).  The output is displayed on an air/fuel gauge, usually in l.e.d. bars or dial.

I can't find a picture of my set-up but it is a common sensor (summit racing/national performance/jegs) and an autometer l.e.d. guage.  I have a handlebar mount that easily allows moving the set up from bike to bike.

This is basically how all new fuel injected vehicles monitor and adjust air/fuel mixtures for optimum performance or cold/hot operation.

Reason I do this?  4 strokes are hard to jet.  Most of the time they are way too rich and run hot, resulting in power loss.  You can set the idle, needle, and main with this set-up.

Example...  my daughters YFZ450 quad stock was around a 148 main if I remember correctly.  After full Big Gun Race exhaust (header and muffler), Cams, Airbox mod, lightened flywheel, and a RevBox the books said a 175-178 main.  After all was said and done, 165-168 is the proper jets depending on season/elevation.  Even a 162 is run at 6000 feet.

2 stroke???  no, I don't jet with an O2 sensor on two strokes because they are actaully easier to feel/look/listen for jetting.  Mostly though because the sensor does not like having the premix on the element and you will have inconsistent readings as well as burn the sensor out, which is a $80 part.  When a modern fuel injected car starts burning oil and wearing out, the residue in the exhaust gases start effecting the O2 sensors in the headers/crossovers, eventually burning them out and messing up the ECM's ability to operate the engine.

Anyways.... interesting topic so I had to throw out my experience with this tool.  I will try and get a picture of my set-up on this thread soon.

Sly

don46:

--- Quote from: js on August 02, 2007, 06:34:28 PM ---the other day I ran into a 2 stroke oil engineer. that was trying to tell me how to read my pipe to get my jetting correct. stating that the first 3" of my pipe would give me the correct info to jet my bike. saying the pipe won't lie like a plug will. anyone got any input.

--- End quote ---

Don't know how you would do it from the outside, are you sure he wasn't talking about the inside of the pipe? I know when the race bikes are jetted right the exhaust at the silencer is a DRY gray.

KXcam22:
Good thread!  I have heard about the pipe "appearance" method.  As I understand it you can get an indication from how far down the pipe discolours.  Now this is 4-stroke only and would never work on a 2-stroke.  I find the whole idea a bit too unscientific for my liking although perhaps it works for guys with much more experience than I have.  The o2 sensor or EGT is the absolute best way to jet a 4-stroke (good writeup Sly).  On a 2-stroke the plug reading is quite reliable, and when combined with some "seat of the pants" impressions, you can get excellent jetting results.  4-strokes are a lot harder since the plug color doesn't seem to vary as much from too lean to too rich.  On my sons XR100 I did most of the jetting by trying a jet in a range I expected to work then flipping the choke on and off to see if the bike ran better or worse.  An O2 sensor would have been appreciated.  Cam.

jigggawatt:
Anyone every try a Infrared Thermometer.

Navigation

[0] Message Index

[*] Previous page