cruzinimage gives me the creeps just thinking of the name, much less typing it.
the 3 different parts i am referring to are on page 56, cb750 parts book, print date 69.4:
1. 16151-300-004, NEEDLE, jet
2. 16133-300-004, JET, needle
3. 16139-300-004, HOLDER, needle jet
myself, i cannot imagine replacing only one of these parts, because all three are wear items and they wear together. replacing one or two of 3 worn parts with new parts, makes no sense to me, but then, there are certainly times i am known to not be the brightest bulb in the package.
all i know is EVERY needle i have ever seen in these non-oem kits is not like an original needle (either taper or length is different) and the one time i replaced the stock needles (for no good reason other than replacing the needles because they were new replacements, the initial throttle opening response was beyond a major hesitation when turning the throttle open.) Going back to oem honda needles took the problem away.
another story, E2241...... on first running of the engine, i had one hellish stagger, "sort of" off idle when motoring off in 1st, especially when shifting into 2nd or even at low rpm in 3rd gear. In 4th and 5th (faster rolling speed and slightly higher rpm's) i could not create the stagger (but there was a sort of "dead spot" in these upper gears.) "VERY ODD," i thought to myself. initially i tried very unsuccessfully to tune the stagger out with the pilot needle screw. then i tried lowering the jet needle to get less gas, because i live at 5,000 feet altitude and thought i might need more air. made stagger worse. so, not knowing any different, i raised the needle, of course more gas, just as bad. and further more puzzling was the fact the stagger really was occurring ONLY between 1/4 and 3/8's throttle open and not with greater throttle openings, so my logic and understanding of carburation relative to air/fuel passageway circuitry at various throttle valve openings told me raising or lowering needle could not correct this condition, because the 3 above parts control AFR's between the entire range of 1/8th to 3/4's throttle valve openings. and the stagger was puzzling because i had not ever encountered a stagger so profound as this, basically when opening the throttle at "take off" speeds, especially profound in the first 2 gears. so bad was this stagger, if too much throttle was given taking off from a stop and opening throttle and even more especially so, when slowing down in a sharp 1st or 2nd gear turn, the engine would "fall" flat on it's face (as if engine dying) when given throttle, then upon slightly closing throttle, the engine would "catch" and the motorcycle lurch forward. (not a good thing if you have a car following directly behind.)
after some thought about the roles each circuit plays separately as well as in concert with each other and what conditions the stagger was occuring and when, i tried replacing the jet needle in all 4 carbs with the after market jet needles from what vendor i cannot remember. the stagger was even worse than ever before, so i KNEW i was on to something. so i replaced the old needle jets with the aftermarket and kept the new replacement jet needles and the stagger was no better. hmmm, i thought..... "that leaves only one other wear part and that is the needle jet holder," which OF COURSE does NOT come in any of the aftermarket kits i am aware of......
so....... i sucked it up and bought Honda nos oem, needle jets, jet needles and needle jet holders, each set running around $45 each, so you can do the math for cost of 4 sets. thought to myself, "this had better be the problem or i'm gonna really be stumped (and ANNOYED).........."
so........ installed the new oem jet needles, needle jets and needle jet holders in each carb and...... NO MORE STAGGER OFF ANY GEAR AT ANY LOWER THROTTLE OPENING.
you can form your own opinion off my experience.
and, of course you know the main jet only comes mostly in to play when the throttle valve is 7/8's to fully open.