3rd down is where you'll want to start out..

I guess you can see that the 352 offers quite a different fueling curve than the N1TC.
I won't taint its' test by rendering a fueling curve description and forecast an opinion of results - but I/we certainly need a detailed ride report..

I will confide this - that needle was designed by DynoJet to fuel lidless running on the KLX300R.

 

Popped in new/ish carb yesterday evening after dark.

I can happily confirm the 4K bog is completely gone-- allowed the bike to warm quite a while went for a 20 minute test-- I was never able to reproduce the 4K sputter, even with the choke on. Fantastic.

Now for the not so fantastic-- bike wants to idle fast and if I turn down the throttle position screw, I can get it down to 1200 or so, but it does not want to idle very smoothly. On top of that, when releasing the throttle from high revs, it "takes its time" dropping back to idle. Not unridable, but on the original carb, dropping the throttle produced almost instant engine braking.

I can confirm the slide drops almost instantly when I pushed it up before I put the carb on the motor, much quicker than my other carb. Not sure if thats more a function of polish, spring, or big slide bleed hole.

Need more time to test, but it appears I traded one problem for another. Im so tired of playing with this &%&$%#. Guess Ill have to work on it some more.

 

Interesting.. I noticed something I haven't been able to learn about on that carb.

That CVK has a system/circuit that I have no knowledge of - It's the "bolted on cover" on the left side with, apparently, ports that lead from the bell to the carb bore area in front of the butterfly valve - between the butterfly valve and the engine. In other words, from one end of the carb to the other..

This system seems to bypass your throttle input and the slide. So whatever the intended function, it appears to be able to introduce air and possibly fuel that is not metered by the slide or butterfly valve(throttle valve) ..

Perhaps that system is faulting and is creating your issues.

 

I wonder if you can swap enough parts onto your carb to find the "culprit" ..

Will the choke plunger swap? Slides? Needle/seat/float in the bowls? pilot jet, Emulsion tube, needle jet, etc etc..


We really need to know what's causing this "stumbling". And you should probably be using your stock carb as there is no telling what all else is non-standard: MAJ, PAJ port sizes - Emulsion tube - needle jet size - etc.. Change just about any of those from standard and your K148 lidless setup would fuel differently.

Aside from that strange circuit on the left side, and its' "hole" or port in the carb bell, that slide looks like it has some kind of hole in it too..

I'm hoping a choke plunger swap will cure your carb, after that a slide swap ....

 

The slide doesnt have a hole in the side-- its just an indention of some sort, just looks like a hole in the picture.

Went for another ride today, included some highway. Fueled up at a gas station, then hit some gravel farm roads and field roads. I put over an hour on it, and I must say, it is running pretty damned good-- I still have kind of a rough'ish idle, but Im also getting decel popping and I think the two may be related-- when I had the carbs apart I should have used the #40 pilot jet and the Kouba fuel screw from my other carb, but I didnt-- I just popped out the aluminum screw plug on the KLX 300 carb and turned the screw out about 3 turns. I dont think its enough-- I think the larger pilot and tunable screw will help there.

As far as the 4K stumble, its absolutely gone! I actually have some midrange power now, like I did before the stumble reared its ugly head-- and the bike is fun again!

As far as swapping parts to find the culprit, if the #40 pilot and fuel screw help my idle, Im going to button up the bike and hopefully not touch the carb ever again. I would love to know whats up with my original carb, but I simply do not have the time right now to continue fiddling with it. HOPEFULLY, I can get the rough idle and decel popping squared away with one more carb pull.

I do intend to COMPLETELY break down my original carb and flush every port and orifice with generous amounts of carb cleaner, check the choke, gaskets, diaphragm, throttle plate, etc.-- but Im not going to install it if I have my bike Kosher with the KLX300 carb. We'll see....

 

1200rpm idle is fine, mine idles nearer to 1600-1800, no problem. My 650 won't smoothly idle below around 1200, never has. Both settle in to that rpm readily, no hanging high idle. With a goofy bar graph tach, who knows.

I don't care if the 250 idles up a bit higher, it eliminates stalling when coming to a stop or stumble off low idle. Supermoto riders set idle fairly high, not sure about MX, for similar reasons... don't want to stall due to low idle.

 

10-4 on the idle speed, but with my previous carb, I had a perfectly smooth 1200 or so. Again though, it had a 40 pilot and tunable fuel screw. I think when I pop them in this new carb I can fix it right up.

Went for a LONG ride today, bike ran great, but its a 100 deg F here now, and Im running the 1" baffle on my DG and snorkleless, + 16 holes drilled lid-- my top end is lacking @WOT , it will barely pull 80 sitting upright-- I previously got 85 or so with a 145 and 138 mains, so I think Im a bit rich for this temp and exhaust. I may try to lean the top out a bit if lidless doesnt help.

 

A 145?

You'll get your top end performance back when you pull the lid off your K148 main jet. Minus whatever the 1" insert robs - which shouldn't be anything as the K148 is chosen specifically for the 1" insert. Otherwise you run a K152.

 

I dont know-- yesterday was 100F with 95% RH. Bike wouldnt hit more than 80 yesterday-- it felt flat up top. In fact, at a point it felft like it wanted to miss/sputter ever so slightly at the very top speed. Felt a bit rich.

I wasnt lidless, but had no snorkel and also had extra breathing holes in the lid. I can try again without the lid, but I dont think there should be too much difference. I can pull it off and check again though, but my current setup helps with the intake grawl. 148 + current conditions might be a little rich for even a snorkel-less lid even with extra holes in it.

High temps and high humidity def affect jetting. Has anyone documented the K152 lidless at 100F/100RH?

 

See for yourself on my DG-R dyno test thread below, that at SAE standard day ( 77°) , the K152/DJ140 would only produce, at the richest point, 13:1 on top. This is borderline lean for max power. There is significant room for conditions to create a richer AFR with no penalty, as max power is achieved with AFR as low/rich as 12.2:1.

The performance of a setup at any particular environmental condition is calculated - no testing required.

Lets see if I can get this right.. Been awhile since I don't fly/pilot during the summer heat. .. Density altitude from sea level on a 100F / 71F dew point day is 2900ft. SAE standard day - which my setups are corrected to on the Dyno - is 1200ft... Jet correction from a K152 puts the corrected size right at a K146..

To summarize: Without the quiet tip, your K148 will be more close to "perfect" on a 100F humid day than it is in cooler/denser weather. I have no data on what a 1" quiet tip does to fueling requirements but I assume it is not huge.
Keep in mind all these AFR variances we are talking about are only +-.75 points - no where near enough to cause rideability issues, but enough to feel losses and gains. All are for lidless running only. As you've found out previously, even your "holed" lid adds enough restriction to alter the power levels.