Jetting - Riddle me this!

[Jakobi]

So I decided to make a few adjustments (again).

Switched out the 40 NEDJ#1 172 to 40 N3CJ#2 178. With the NEDJ the bike would idle and idle and idle and start so easily, hot or cold. Same needle diameter, same air screw setting, same slide height, but different needle and the bike just doesn't want to start as easily. Can get it to fire up in a few kicks and it runs really well from idle and above, but it just won't maintain an idle on this needle. Winding the idle adjustment screw in to raise the idle to an acceptable level results in the dreaded racey inconsistant idle.

Any thoughts?? Visibly there seems to be more smoke with the N3CJ needle (I know not to jet by smoke) and we all know the needle runs a rich -> lean taper profile. You'd imagine the leaner profiled NEDJ would exibit a hanging idle due to a lean condition over the N3CJ. Coming out on the air screw might help some.

Generally this newer setup needs the throttle opened some to get it to fire. Just not sure if its because it needs more air or more fuel. All ideas appreciated.

 

[noobi]

Do you have jetting based dreams or nightmares?

Although, your predicament is curious, logic would say same diameter needle in the same position would yield the same results. Maybe its just your bike trolling you...?

 

[Neil E.]

Manufacturing tolerances. Check the shank diameter with a micrometer.

Measure the L1 length. Maybe you got the runt of the litter.

 

[gasgasman]

Carb is "worn out" from being disassembled too many times.

 

[MrBlah]

what slide are you running? It sounds like your having to raise the slide a bit to maintain idle, and the needle is bleeding into the idle circuit

I know on my 36mm I absolutely am bleeding needle into idle, changing the needle always makes me have to adjust idle and sometimes airscrew, I think I need to put a 8 on mine

 

[Jakobi]

*chuckles*

You're probably all on the money. The dreams are somewhat hellish! The logic is what puzzles me.. I'd not be surprised if the bike is taking a lend of me. The weather sure is! I might take Neils advice and give em a quick spec up.

A quick ride should let me know how its all going. Most people suggest a lean pilot = hard starting. Opening the throttle generally leans it off too though which is what i need to do to get it to fire. Opening the air screw more results in a better idle which makes me think I'm rich on the pilot still, but then results in a high idle after a blip of the throttle. (Even just a very small blip - or winding the idle screw in 1/4 turn).

Its got me right puzzled.

 

[Jakobi]

what slide are you running? It sounds like your having to raise the slide a bit to maintain idle, and the needle is bleeding into the idle circuit

I know on my 36mm I absolutely am bleeding needle into idle, changing the needle always makes me have to adjust idle and sometimes airscrew, I think I need to put a 6 on mine

I am running a #7 without the notch. I think this might have something to do with the hard idle aswell. I dont think I'm pulling off the needle. I know I have in the past with a F and G diameter needle where the idle screw was wound all the way in to sustain a very low idle.

 

[Jakobi]

More Q's for the wise..

Essentially I continue to end up in a catch 22 where if I back the air screw out, the idle lifts and sounds better, but the idle will then hang a bit too high after a light opening of the throttle before dropping back into its nice idle. Leaning off the AS further increases the length of time the idle is high. If I screw the idle adjuster out some more the idle will drop back down, and continue to get better as I lean off the pilot until the hang starts again. Does this mean I'm moving in the right direction??

Alternatively, if I consider the hang to be a lean condition, turning the AS in and richening the pilot will stop the high idle, but then the bike is too rich to idle and I have to lift the slide (turn idle screw in further). This again will either cause a hanging idle, or continue until the off idle response is so rich that response is sacrificed and burbling is present.

Is it possible I'm still too rich on the pilot and pulling over a bit? Or am I too lean on the straight diameter which is causing a hang after a little blip? too lean on the needle completely causing a hang? Richening the needle diameter means I need to drop the pilot again to get the idle and response and I fall into the same catch 22. Richening the needle I end up with rich burbles around the 1/4 throttle and above that can't be tuned out on pilot.

 

[Neil E.]

This sounds like where I've been with jetting. The low speed jetting doesn't work quite right and it's as though the circuits overlap too much. You wind up with extreme adjustments to make a difference. When I removed my AS and disturbed the thread sealer, the problem got MUCH worse. You probably haven't removed yours, but have done enough adjusting that maybe it's not as solid as it used to be. It only has to move a few thou to change the idle characteristics. It's very confusing since the slide settles more after idling for a while.

When I was investigating, I removed the slide stop screw spring. With the throttle open, I would press down on the screw and when the throttle closed I could feel the screw move as the slide pushed on it. To anyone reading this: don't remove your slide stop screw! This will disturb the sealer too much and you'll have the same problem. Maybe you should try a really heavy slide spring as an experiment. See if the extra force overpowers the screw into a more consistant postion. The sealer acts like blue locktite in that it has a white flaky appearance once the screw is removed. Being that the screw is plastic, the sealer only has a limited grip, and screw can still turn.

Note that any M5 x 0.8 screw will have a sloppy fit so using a standard screw as a replacement gains nothing. Here is another thought: if you can find a screw with really long threads, point the end to match the stock screw, then use a washer and locknut in place of the spring. This might lock the screw securely enough for testing purposes. Once I had my custom brass slide stop screw installed my idle improved dramatically. It is rock solid at the speed it idles at, but I still have different idle speeds under different conditions (fast idle when cold, slow idle when hot).

 

[Neil E.]

Can you get back to a previous known GOOD configuration? Since you have had some good needle/pilot combos, I'd say "what changed"? If you can get back, then my comments about the stop screw play wouldn't apply. I think "large shank/small pilot" is still the best approach to get the slide down to prevent pull-over.

 

[GMP]

It stands to reason that a new 36mm carb on either a 250 or 300 will have a greater signature and therefore more sensitivity to any changes than a 38mm.

What does the nozzle shroud look like? I had a KTM with a sloppy carb casting and flash in this area. Cleaning it up seemed to help. I think Ron cleans this up as part of his carb mod package.

Question for you guys: Do you think the older AS carb will fit on the '11 and clear the tank?

 

[Jakobi]

Neil E. I have always had this issue with the N3xx range of needles. Its always been a juggling act. Maybe they have a shorter straight section?

The NEDJ with the 40P AS2 will idle on and on and on and start first kick every time, hot or cold. Dropping in a N3CJ I'm experiencing harder starting, with the idle I spoke of. Previously using the N3CH with a 38 pilot I had the same issue. I don't think its the idle screw/air screw moving. Both hold position and it wouldn't make sense that it changes with differing needles.

Glen, my 2010 EC300 is running an ASII but 38mm body with a 17mm float drain. I believe the 36mm's use a 14mm drain plug. I'll check the nozzle casting today.

Not sure about the older style carbs fitting. As it is to rotate the carb back in the throttle cable touches the under side of the tank and the bowl is quite close to the cases.

 

[MrBlah]

I'm surprised your remote choke is not leaking air yet, I thought that was the first thing everyone removed

 

[boyscout]

Question for you guys: Do you think the older AS carb will fit on the '11 and clear the tank?

The old srew top type carb fit fine on my 2011.

 

[TNT Cycle]

It stands to reason that a new 36mm carb on either a 250 or 300 will have a greater signature and therefore more sensitivity to any changes than a 38mm.

What does the nozzle shroud look like? I had a KTM with a sloppy carb casting and flash in this area. Cleaning it up seemed to help. I think Ron cleans this up as part of his carb mod package.

Question for you guys: Do you think the older AS carb will fit on the '11 and clear the tank?

My 2010 is the same frame and tank as the 2011's and has old carb.

 

[Jakobi]

I'm surprised your remote choke is not leaking air yet, I thought that was the first thing everyone removed

Has been changed since the picture

Didn't like that it could hook up on branches and vines while riding. Old plunger one has been fitted

 

[GMP]

OK, now the next question is would an original PWK AS carb fit on a '12? Someone, likely me, will find out. Seems like the new carb is a real PIA to a lot of people. My '07 is jetted flawless, and it would be nice to try that carb on a new bike just for kicks.

 

[Jakobi]

They are mega PITA!!!

I have just pulled my carb cleaned it out, checked the reeds, slapped a fresh plug in.. I made sure to set the slide so that it was only just open and confirmed on the straight diameter. Tried a 38 and a J - too lean and poor mushy response. Went to a 40 and a W - won't idle unless coming out 3.5 turns on the air screw. It doesn't hang. I'm going to try and drop the J diameter in with the 40 and should hopefully end up where I was before.

I have also lifted the needle clip half from N3CJ#2 to N3EJ#1. I had tried N3CJ#3 - wouldn't run clean. N3CJ#2 cleaner and N3EW#1 cleanest. All with a 175 main. Not so suprisingly though, I am essentially back at what I was running 12 months ago when I bought the bike (hot summer months), with exception being I was using a N3EG and well rich, pulling over and still burbling at lower openings.

/end rant.

I'm hoping if I get a 2012 EC250 that I won't have to go through too much of this again.

 

[Neil E.]

I'm surprised your remote choke is not leaking air yet, I thought that was the first thing everyone removed

How can you be sure the choke is leaking air?

 

[Jakobi]

Same as any other air leak Neil. Will cause a racey idle but will also change revs if you spray the area with some wd40. You might even be able to make the revs change just by playing with the cable.

You can always unscrew it and check the seal aswell. My handbar mounted choke had no issues with it not working properly. I just kept hooking it up on vines and weeds when bush bashing.