Update: PWJM and I disassembled our carbs and compared the components of the primary fueling system...

All measurements were identical with a tiny variance likely caused by the fact that we were using two different calipers. Mine was "zeroed" correctly, but PWJM is Canadian - so you know...

Needle jet + main jet protrudes from the casting boss the same amount.
Needle jets are the same in every way.
Collars are the same.
MAJ's are the same - About .016" -.018"

It was a marathon messurin sessun...

So I still have no idea how his carb is overfueling the midrange..
He has a TM coming and will hopefully send his "magical carb from hell" to me for an old fashion medieval exorcism..

 

As an update, I just ran the carb with a DJ132 and the needle at 2N today and it was still overly rich in the mid range. Not sputtering under load, but there was throttle hesitation and poor response.

I don't have a 130 or I'd try it, but I'll give it a go with a 128 next. Even thought these smaller jets are working, I've tasted the top end power with a 138 and will be sorely missed. I can't give up that mid range when offroad though. It's a necessity.

Weird carb....

 

So now on to Snowdrifter -

It seems PWJM will have to run very VERY small main jets. Have you tried stupid lean setups - like DJ128/3N lidless?

I know you are lower than his 2k ft ASL.. His bike did run 99.5% at sea level with 138/3N..

 

If it's the correct one (KLX300 part pictured) I thought it had more holes than the 250cc stocker. I had one that I tried but ended up removing it; can't find it right now or I'd have a look-see.

 

That's something I've not seen in any of the carb threads, a change in the needle jet. Maybe I missed it. All the changes I've seen using KLX300 parts only involved the needle itself.

Just mentioning that observation, not saying that's the issue.

 

I can confirm I haven't changed the needle jet, only the needle.

The one pictured is VERY similar to mine but not EXACT. the location of the emulsion holes is slightly different.

My needlejet is identical to klxster's in both measurements and design though. Two of the quadrants have 3 holes, and the other two quandrants have 5 holes (as pictured).

 

Did some measuring of my own yesterday. Measured the holes in the DJ jets that i have . The jet numbers go up in increments of 4 so i assumed that the hole sizes would also be incremental. I used a drill set with small drills as pin gauges measuring each drill with a micrometer.
Stock jet which came with the bike, hole size Ø0.043"
DJ 112 = Ø0.043"
DJ 116 = Ø0.043"
DJ 120 = Ø0.046"
DJ 124 = Still in my carb ?
DJ 128 = Ø0.050"
DJ 132 = Ø0.054"
As you can see no consistent incrementation. 112 and 116 same size. 116 to 120 0.003" different and 120 to 128 is 0.004" with a 124 in between.
What I take from this is that the difference from stock to DJ 132 is only 0.011" , not a lot. Which means that 0.002" could have an affect on the running of the bike.
It would be interesting if others could also measure their jets for comparison. Maybe DJ' s quality control is lacking.

 

I think jetting is more complicated than diameter. How the hole is ramped & the viscosity of the fluid would effect the flow.

 

I agree with you on this, however if the ramp or taper,chamfer whatever is required for optimal flow then it would be applied to all jets regardless of hole size.Therefore all jets should be the same with the exception of the hole sizes.
I manufacture piston rods for natural gas compressors which have rolled threads on each one. They require a certain chamfer to start the thread, which is applied to all rods no matter of thread size.
So to me hole size is the defining difference of jets(only if made by the same manufacturer in this case DJ).Other manufacturers may have some thing different. If ramps define the jets and not the hole then all holes will be the same.
JMHO.

 

thanks for measuring those jets Wack!

I've got nothing to measure mine with unfortunately. Would be interesting to see what my 132, 136, and 138 measure up at.