This is a long post because as usual I go into detail with what I did

to sum it up, I had weird idle issues after enlarging the pilot jet to get rid of decelerating popping
well I got that fixed now, but had weird idle drops at stop lights
I put the fuel screw to 2 turns out, from the original 3 I had set it at with the dynojet kit

Seems like it may be fixed but I ran out of daylight and heat to be totally certain




The details


Seems like all my bikes used air fuel screws, and I know how to set those

only 1 bike I have and my klx has the fuel screw under the bowl
ive never learned how to adjust that never needed too


Since I had installed the exhaust, and header and dyno jet kit I put the fuel screw where it said, 3 turns

From another thread I used an air fuel meter to get my main jet set, so that jet is not an issue here


Now since I had alot of popping on deceleration ive slowly been drilling out my pilot jet one size at a time, and its almost gone now I say 99% gone

I started at a #80 drill bit that also happens to be the smallest one I have
I use this on all my bikes when cleaning out the pilot jets because I buy old bikes and they are always clogged
It is larger then a 35 jet as it does drill through I cant find any charts that go this low. The lowest I can find starts at a #76 drill bit = a 50 jet
But I believe the #80 is a 40 jet size



Since it seemed like the stock pilot jet was a 35 I used my smallest drill #80 and took a couple rides this was done maybe a month ago
recently it seemed to be popping more

then I did a #79 few more rides popping got way better, and stopped at #78 drill im guessing this may be a 45 jet now

here I realized my header to muffler clamp was a touch loose, I saw soot on the joint. I tightened it up alot more. This may have added the additional popping. I may not have needed to enlarge the jet, but that was done and no turning back now




Ive been riding it on a off for a while now, but only the last 2 days ive noticed the weird slight idle drop at stop lights
every time I hit stop lights it would be a touch fast idle, maybe right at 2000 only because I have been adjusting the idle up because it would drop some
then takes a minute it will drop to 1700-1500

its enough you can hear the difference
I would fiddle with the idle screw but you dont have much time at stop lights
So I never really got it set


When I had a chance I had set the idle to around 1700, not sure what its supposed to be never checked but it sounds about right from how I always remember it sounding
at one stop light after a minute it dropped so low it died on me
first time this ever happened
the weather is a little cooler too since the last times ive been riding, not sure if that would effect more


When trying to set the idle at home I did notice the air box intake hose had slipped off the carb maybe 1 inch, could of had an air leak
hopefully from the last time I drilled the jet
I thought this was my idle weirdness issue but no it keeps dropping just a little after a min or so at a stop light
it may have not had an air leak, but I did get it set back on nice and tight now



So im guessing the fuel screw needs to be adjusted since the pilot jet is larger then stock

And its really fun getting to the screw and I can see no easy way to but spin the carb over to adjust

so this is something I cant do with the bike running, unlike idle air screws which you adjust with the engine at a fast idle
or is the bike supposed to be running to adjust
if so how can I reach that screw?


anyways I tried 2-1/2 turns took for a quick ride not much change, still did the weird idle drop

next I did 2 turns,getting dark and too cold now to test but got im one long ride trying to hit all the stop lights I can

at the 2 turns it will barely drop at a stop light after 1 minute maybe 1 tick on the tach, so maybe 100 rpm?
and I may be crazy but it may be back to how it was before any of this jet drilling
how I remember it sounding, I do have almost 7000 miles on this bike so I have had enough time on the bike to know all the sounds and noises it makes


but what I wanted to know is whats the proper procedure for adjusting it


because im thinking maybe I will order another stock jet and just drill it to the #79 drill and leave it there


I am glad I took the time to enlarge the pilot jet really got rid of the popping
but im hoping I can figure out the fuel screw just so I can have the normal smooth idle I always had
It may be fixed now, but I will need to do one more test tomorrow just to verify

 

More often than not, with proper pilot jet size you should end up somewhere between two and three turns out. More than thr More than three turns may not allow the spring to secure the mix screw. Less than two maybe may not give adequate clearance to avoid clogging with any miniscule crud that may come through (a guess). I will say I'm not much for drilling jet since the drilled surface finish can actually cause a drop in flow - as a friend learned and fluid flow teaches, but that's my choice.

The only method I've ever known to adjust an idle mix without any sort of instrumentation is as follows. Get the engine idling first, continue to turn the mix screw out until the idle drops, then, counting the number of turns back, turn it in until the idle drops again - split the difference of the number of turns. I.e. 1-1/2 turns from high idle lean to high idle rich, turn back 3/4 turn. It is a compromise, but all hard jetting is a compromise. I usually know how many turns out where I started, but if I don't know I will turn it in after finishing just to make sure it is not turned too far out.

There is a range where the engine will hold close to the same idle and you are splitting the middle. If you are on either extreme the air temperature and probably humidity can affect the idle making it either drop or idle down weird. Hot air is thinner - rich mix - cool air is denser - lean mix - don't know enough about humidity. Plus altitude, if that changes significantly, is another issue too.

At the bike shop they used to use a special tool tachometer that would read I think as low as 10 rpm change. It enabled them to adjust the mix very close by seeing that range much closer than by feel, ear, or the "tach" on the bike (the electronic ones have I think a couple hundred rpm per bar and the older analog may have float) especially helpful when setting up to balance them.

By the way, with the screw at the mouth end of the carb (like most 2 strokes)it usually controls the fuel added richening mix, screw at the inlet/cylinder end (like most 4 strokes) adds air leaning out mix. You only need to know so that you know if you need to go richer or leaner on your pilot. There may be some different set ups on some carbs, but that is th case with Mikuni and Kiehin carbs.

 

What altitude are you at, what size main jet, and what notch is your clip on? Float height?

I'm no expert at all but here are my thoughts from my recent jetting woes:

The previous owner of my bike had a #45 pilot on it and it was just too much. Bike always ran a bit too rich even with mix screw out just half a turn. Major loss in fuel efficiency without performance gain. I'm making a thread tomorrow with more details and pics, but I wouldn't think #45 pilot would be ideal for you. It may be fine if your main jet isnt too large but it would not be optimal AFR curves. If you prioritize idle first you may be detrimental to higher opening circuits.

Probably better to go to 38 or 40 pilot max if you're close to sea level and go bigger on main jet and notch depth to increase richness.

 

well since I did the jetting a while ago im at the max jet dynojet provided I think a 134
I will have to go check
I kept the air box cover on but did a large hole in it to get the air fuel ratio correct at full throttle

and the needle was whatever they said to do in the instructions, using the new needle
supplied

and im at sea level


I will probably order a new pilot, keep on hand and see how this setup works for a while




I did see videos of people buying some extended fuel screw to adjust easier
I will look into that, as there is no way I can have the bike running to adjust the screw
even if I made a 90 degree screwdriver I think the exhaust pipe would risk burning me

 

ordered a 38,40,42 and some little tool maybe can adjust the fuel screw from jets r us
for $7 more then 1 oem jet from my dealership


so that way I wont have to drill them, and can try them all and know what size they are exactly

and im going to check with my drills to these jets so then I can know for sure what size the drills are close to also

 

With those pilots jets, you'll have the pilot system under control. What you can do now - since I know you don't like constantly pulling the carb for tuning sessions. - Call DJ and get a #136 main jet coming ($2.00).. Based on the latest findings on non-MCM bikes at your altitude, you'll need a #40 pilot, #136 main, 4th notch on needle, lid off.

If you were to have a stock #35 pilot, that would change to 136/5n and 3+ turns out on the fuel screw..

Now if you still have access to that AFR meter and want to experiment, order DJ #136, #138, and #140 main jets

I'm thinking your slightly more restrictive DG-O (with ChinaBomb) compared to my PC4 (with Megabomb) will probably achieve a more favorable WOT AFR with the #136 than my full FMF data - I am needing a main jet larger than the #136 as AFR's are too lean up high where that FMF system wants to make big power..

 

well the long ride I did today it would average sitting at around 2000 rpm
then after a min or so at long lights it would drop to maybe 1800

Im pretty sure I used to keep the bike around 1600 but when I try that low, it seems to really drop low when at a long light

so I dont think I fixed the problem with the fuel screw like I was hoping, but its not as bad as it was yesterday either

I also checked for any intake leaks, and on the smog stuff I had capped and no leaks

so pretty sure its the pilot jet

once new jets are installed I will post back if it helped

probably going to use the 40 jet, and the 3 turns out as a starting point

 

and yes my main jet is a 132
with modified air box cover
as when I did the fuel air ratio with air box lid off it was leaner at full throttle speeds

so whatever size hole I did in the air box lid made it perfect

if I was to go to a larger jet, then I would remove the air box lid completely


needle clip is down 3 from the top right now



and ive learned how to change jets without pulling the carb, once the throttle lines are removed I can just twist it enough to access the jets, so its not as bad as the very first times I did it

as for the needle, maybe I can access it twisting the carb over not sure

 

I'm at 900 ft, using a Mikuni 40 at 2.5 out, didn't do any adjustment since it worked fine right off the start. I did the KLX300 brass per the cheap mods and it all worked fine with the Dial-A-Jet to add fuel when lean, so I got nothin' on any DJ stuff.

 

Throw all the jets you drilled away.
Put a new jet in and do what klx678 sayes.
Get a angle screw driver or something to adj the jet with the bike running. If you go over 3 turns out, put next smaller jet in. It doesn't matter if it is an air or fuel jet, if it is too big, it is too big.