All 2st jetting your two-stroke...

an impropperly jetted bike can be frustrating and cause engine damage.

first- let's look at how a carb works. it has circuits. these circuits meter the fuel to the engine based on throttle opening (TO). if you are having issues with a bog or gurggle or what not, identify the TO the issue is at, and, the corresponding circuit. then, make the adjustment. make one adustment at a time. then, retest. there is no magic to it. it's very simple and once you know the sequence of events you can tune your carb everytime an issue comes up.

http://www.cafehusky.com/forums/showthread.php?t=8039

when you get your new bike home. read the owners manual. it may not be exact but it can get you in the ballpark for running in and to start with. if you dont have one, find the info online or from the maker.
always verify your jetting before taking it out on the first ride, breaking it in etc. otherwise, you'll just be chasing your tail. dont go nuts trying to make it perfect just doing heat cycles in the garage when it's new. just let it idle, warm up, cool off, et al. once it is broken in and ready to put a full load on the engine you can begin your baseline testing.

start with a machine that is fully ready to race or ride. no mechanical issues etc. it must be 100% good to go and serviced.

main jet- see corresponding circuit in the diagram above:
start with the main 2 sizes over the recomended, the needle clip (the clip) in the middle and the air screw 1.5 turns out.
warm it up and get it cleaned out as much as practical.
install a new plug in a warmed up engine.
start the bike and jump on, go WFO in first, second and at least third gear....then, pull in the clutch, chop the gas, hit the kill switch all at once. do not let it idle. then, read the plug. dark brown? we are safe for now and ready to go to the next circuit. if it is lighter than that, it's lean. black and oily? go down one size and redo w/ a new plug.
always do main jet verification with a new plug. so what, you'l have a few extra plugs. you do change your plug every now and then, dont you? you can use the standard non-race electrode ones for this to save money, i use them all the time. then, go to the big bucks OEM fine-wire type later if you want to. so long as it's the same heat range, reach and R-type you are fine for most dirt bikes.

idle and off idle in neutral:
how's the response? does it bog? if so it's too lean. adjust the air screw in 1/8th turn. if you go in more than a full turn or so, turn it back out to 1.5 turns and go up one size on the pilot jet (PJ) and start over. this will give you more room for adjustment.

in gear roll on:
lets say our off idle snap is ok but it bogs rolling on from 1/4-3/4 TO. try to identify as closely as you can when/what TO the issue starts. slow down and don't whack the gas wide open. try to get the issue(s) to present itself while you roll on the gas as slow as you can while still getting it to act up so you can more positively identify the circuit that needs adjustment. see the chart and adjust one item, be it the PJ, the clip or the main (most likey not but dont rule it out).
if you find you are at the bottom notch in the needle stop- go back to the middle slot with the clip and go up one size on the main and restest. never lean it out with the needle more than one notch. try a leaner needle (always go back to the center notch) or main and reverify. always reverify a new main with a new plug using the WFO, chop, etc. method. always start rich to be safe.

once you get the circuits dialed, you'll really only need to change the main when going up or down in elevation....sans a minor tweak of the air screw if nec. this is why i always run a needle that has it's clip in the center or as much so as practical as it gives you room for adjustment and flexability.

here's some more tips:
keep track of your work- make notes as you go along.
write your recipe on the floatbowl with a sharpie.
don't toss a bunch of parts at the bike at once, you'll never get it sorted it out. make one change at a time, this includes pipes, mufflers etc.
if it pings or run's on at idle (gaging, ging, GING!) or does not pull and sounds flat it's lean. STOP! and richen it up a size or two on the main.
if it's too rich it will foul a plug and be blubbery/gurggle.
better to foul a plug then burn a piston.
if you are on the cusp of lean it will lean out even more when the piston gets hotter when the going gets gnarly and slow. account for this accordingly.
the engine will make more power slightly rich then lean, and, wont burn up the piston.
99% of your issues are caused by lean air/fuel ratios as bikes are so dead nuts realiable today unless it's a known product problem that should have been addressed BEFORE we started this, it's jetting that is causing your issues in most cases.
always take spare plugs and jets on the trail.
always drain your tank and carb after riding.
never try and jet a bike to match the performance of another bike, be it the same or another make.
never take someone elses recipe as gospel, are they gonna buy you a new motor? test and verify.
pay NO attention to spooge, if you do, you are looking at the wrong end of the machine and asking for trouble.
125's like BIG main jets.

jetting is simple. it takes no special skill, just patientce and persistance. be methodical, not radical.
do one thing at a time and use logic.
don't guess, address the situation.

i seriously aint that bright and am not even close to being a genius but i have yet to own a bike i cant jet. my 09 WR 125 runs perfectly and is stone stock with the mik carb and all. when i got it home it would idle, and that was it. i tossed a leg over, snicked it into gear and it bogged so hard i almost dropped it and it would not go down the driveway. so- i rejetted it using the OM as a baseline. what was in the carb wasnt even close to the OM! the OM still wasnt exactly correct but, it got me started in the right direction. almost every dirtbike i've ever owned was the same way, way off!

again, unless you have a mechanical issue, that rarely causes a bog (PV's excluded but those have been addressed to DEATH and no one should have those few bad one's that got out anymore) but rather a failure or no-run situation, your jetting is probably off a little somewhere, and, most likely not everywhere.

bottom line: find the problem circuit and adjust it and it'll scream and run perfectly and start just fine. i gaurantee it.

Good write up!

Thanx

Darin

Thanks for the great write-up....

Some times patience and persistence are special skills.

yer welcome guys.

coffee, could you please make this a sitcky here in the "two-stroke forum" as it might help some of us out trying to jet their CR's/WR's.

thx.

good suggestion matt and it works as you described.