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Starts on first kick, idles, but constant blubbering in the 1/4 to 3/4 throttle range.  Full throttle takes off like a scalded cat!  Needle clip in top groove, new needle-setter with good O-ring, and 130 main jet.  Pure smooth power kicks in at around 4,000 rpm.  First part of vid is gentle mid-throttle acceleration through the gears; last part is full throttle.  (2 minute vid)
Could sure use a little guidance from the EnduroWizards!  Cheers, Pat
 

One possible cause for those symptoms is wear in the needle and needle jet .
OEM part numbers are needle  438-14116-08  ( 5EJ8 )
                                needle jet   445-14141-38  ( 241  O-8 )
A thorough ultrasonic clean of the carb would be a good starting point , before actually replacing hardware .

+1 on Swoop56 comment regarding the needle and needle jet. Replacing those items on my DT400B and DT250B absolutely eliminated the blubbering. Unfortunately I cannot find anyone selling the needle jet 445-14141-38 for the DT360A. So on my DT360A I only replaced the needle. MarkT shared info on a more common alternative 159 needle jet that I plan to try this year.

I'm with Swoop56. Worn needle jet. Alternatively havev you got you idle mixture screw fully in!! Instead of 1.5+ out. Is there something blocking the air feed to the needle jet--have a look. Had the slide guide pin gone walking & slide has turned. Oring should be good or would never clear on full song. Back to Swoops thought though. Worn needle jet, the metering bit at the top.

stock 241 jet, VM30SS 


159, Q-6


159, Q-6


L=159 Q-6, R=241


159 jet from a VM30-83 in a VM30SS w/the 6 series needle from the 30-83. Ran a lot like a VM30-83 in this configuration.


241 in a VM30SS

Gotta be careful that the tall top jet has the right slide for clearance when throttle is closed. Just saying.

Swoop56:  thanks for the OEM part numbers and the ultrasound cleaning suggestion.  The needle and needle jet I have installed are aftermarket...most likely VM30-83.
Schu:  found MarkT's post on the 159 alternative...thanks man.
RT325:  I've tried the idle mixture screw in every position between 1.5 - 3.5...doesn't seem to affect blubbering.  Yes, the slide pin had gone walkabout but I fashioned a tiny screw with Loctite that seems to do the job.  Will definitely check the slide clearance.  Many thanks!
Pabdt:  Great pics and notes brother!
This old thumper has been with me for 52 years and we both appreciate the vast amount of shared knowledge available on this very useful and friendly forum.  
 

Can someone please tell me which of the small intake side openings is the air-jet?  Is it the middle one?

Just another random thought seeing you confirmed the slide pin had been repaired-- not a different slide with slot on the opposite side so you end up with the cutaway the wrong way around? That does pretty much whst you have, rich up to about 3/4 throttle. And one more, the needle jet the right way, has a side pin for orientation at the bottom.

Oh sorry, I misunderstood earlier.  The throttle slide is fine, original pin in place, slide facing the right way.  It was the needle jet pin that was lost and I had to replace and it is facing the right way also.  In the meantime I found a 5EJ8 needle and put that in last night and will test it today.  None of the other three needles in my collection have that inscription.