Hill Johnson (BINSYS) is a member of the Intruder 1500 Forum and has done some extensive testing on the LC Carbs. He's a good guy and certainly one of the more mechanically inclined on the group. Got a question go to the forum and look for BINSYS. He posted the following findings to the group, I liked it enough I asked his permission to post it here.

DYNOJET vs FACTORY NEEDLES
BY HILL JOHNSON (BINSYS)
Reposted with permission:

THE SHORT STORY:
For those of you unwilling to muck through the whole thing - the Dynojet needles at kit recommended clip positions are TOO RICH, based on field testing.

If you are using richer pilots (#40+), and a dropped needle setting, you are probably masking the needle circuit entirely and unneccesarily. There is no good adjustment (clip position) on these needles that is exactly suitable for the entire carb circuit on the LC, keeping everything else reasonably within spec.

BACKGROUND / QUALIFIERS:
HC, GMAN and I have been having a lot of backchannel conversation lately, trying to work out problems specific to the Pro Pipe. Since I work for myself, I have had a bunch of free time to do nothing but waste tanks and tanks of gas doing 0-90 runs in the country, while having the covers off, bike festooned with all sorts of adjustment gizmos, vacuum guages, etc. I have two (2) sets of LC carbs, both similar in milage and wear.

The spot I go to is also just far enough away for a good test of smooth cruising power, a few hills, a few straights, etc., as well as a good area not to get caught speeding doing a lot of WOT.

I have been working on very, very fine adjustments based on HC's basic recommendations. Over time, I have tested setups which were way outside those, including much larger pilots (#40, #42.5, over 3.5 turns out), and every main jet size from #172.5/#170 down to the current crop of #155 / #157.5, on various bikes. I have been tuning bikes direct from the sales floor for about the last four months, over at Limey's house every Friday, as well as some older models coming by, and riding every one when done to check results. We have also been riding with some of those people on weekends, and seeing what goes faster, who can get the jump, etc.

THE TEST CARBS: I have a California emissions regulated carb with the emissions stuff disabled, and an East Coast carb with no extra emissions stuff. Both carbs have about similar wear (21k & 18k), both have been running Dynojet needles since about day one, and both seem to perform exactly the same when setup exactly the same. I don't think there are any specific wear problems to report about Dynojet needles here.

HOW I GOT CONVINCED TO DO THIS TEST:
After tweaking, tweaking, and more tweaking with carb tools, remote adjusters and vacuum guages, I was finally satisfied that I could reproduce the best possible running with the Dynojet needles installed, and both sets of carbs were behaving the same. The bike was running very, very strong, getting good gas mileage, and both sets of carbs could be made to do pretty much the same thing.

HOWEVER - I had a few nagging issues, which I at the time associated specifically with the use of the V&H Pro Pipe - now, I am pretty sure they are not related.

ISSUE #1:
Excessive popping. The Pro Pipe and another 2 into 1 system I have been working on seem to have a lot of difficulty getting rid of popping. Both happened to have DJ needles.

ISSUE#2:
The Pro Pipe seemed to want to be run as lean as possible on the screws to get any oomph out of the bottom end, and getting it to run that lean caused poor idle, and made it harder to tune out the popping. Opening the screws too much also induced 'throttle fade' (see below), although one trick to get rid of popping is to set the screws too rich.

ISSUE#3:
What I am calling 'throttle fade', which HC had not gotten symptoms of in any of his testing. I found it early on using the larger pilots and main jets - loading the bike in 5th gear (such as going up a grade) produced slack in the last 1/8th throttle. As I reduced main jet size, this 'fade' lessened every time until I arrived down at HC's main pilot jet recommendations. Opening the screws too far on my bike also caused throttle fade.

ISSUE#4:
When I finally was able to repeat every time what I knew was the best I could do, I still had a nagging notch in the needle circuit in the midrange, sort of a little blip that would happen consistently around 4000 rpm. I could move the rpm where the blip occured by changing the screw settings, but could not get rid of it entirely. The popping was still persistent enough to annoy me.

SO I AM IN A FUNK, AND HAVE NEED FOR A FIX:
My comments to HC about the blip, the vacuum balance, the popping, and the need for really lean pilots, should have been the clue, but weren't. Last time I talked to him, I mentioned I thought the rear needle was going lean at that point where the blip was, I assumed it was a needle transition, and needed just a tiny amount of shim to take it out, perhaps .10.

I also mentioned to him about wierd results I had gotten by unbalancing the carb sync toward the rear, when I noticed the idle going up on the rear when I moved the synch screw that way. We both thought it was kinda nuts, I sounded like I was talking out of my hat, but I think I can now explain that also...

THE TESTING:
Not having a .10, I tried a .20 knowing that that might be a little much but would probably smooth out the the 'lean' rear needle. To my great surprise, the problem worsened, and made me rethink my whole aura, dude... it HAD to mean that the Dynajet needle in the rear carb HAD to be too rich...

Having an extra set of carbs, and a lot of extra carb parts is a good thing. On a whim I decided to set up the other set of carbs with stock needles, one shim each, and use HC's last published screw settings (already using same jetting). I misread them a little, and set them to 2 7/16r - 2 9/16f.

SURPRISING RESULTS:
Although the throttle stop was too low, the bike idled immediately better with no popping even at the low idle speed. Setting the throttle stop up to the proper rpm produced a very clean, even idle, with NO popping. Taking the bike out, it ran like a tractor with a hemi on steroids. Absolutley no weak spots, uneveness, or throttle fade anywhere, even though the screws were a little richer than I had previously liked. Something was clearly up!

ANALYSIS: WHY WOULD IDLE QUALITY, POPPING AT IDLE,
& PERFORMANCE ALL BE AFFECTED BY JUST THE NEEDLE CHANGE?
After I got these results, I really decided to thoroughly compare the stock & dynojet needles side by side on the bench (I had enough extra sets, which most people might not have lying around).

When lining up the clip positions on the the stock needles and the Dynojet needles, compensating for the shim position, it was pretty obvious that the rear needle (which was causing most of my problem) was much shorter and therefore much richer than a stock needle with a shim. The taper appeared slightly different as well. The front needle, which seemed to be able to be tuned consistently, was much closer.

OBSERVATION #1:
First of all, the rear needle was obviously too rich setup as described in the kit. Further, the adjustments available on it (clip positions) could not equal a stock needle with one shim.

OBSERVATION #2:
Slight differences in needle taper. This is where the real revelation was. Can you guess?

OBSERVATION #3:
I had in the past noticed, and not paid any attention to, under certain conditions, fully closed needles leaking a small amount of fuel, such as when coming down to idle from being revved up.

CONCLUSIONS:
The rear needle, being obviously too rich by simple sight measurement speaks for itself.

In thinking about needle taper, it suddenly occurred to me that if the taper was even slightly different than on the needle seat, the seal would not be as good as a perfectly matching needle and seat. The stock needles would by design match perfectly to a high degree of precision.

This would not affect operation much when the needle was supposed to be partly open, but when it was closed and supposedly tightly sealed, if it passed even a small amount of fuel or mist, it would affect operation at idle or slow point in the circuit.

This would account for popping (if a small, uneven amount of fuel mist came from closed needles), uneven idling (for the same reason), and generally a requirement for leaner screw settings (passing more fuel into the whole circuit when lifted less). This would also absolve the Pro Pipe as the culprit (I am glad about that - I think it makes my bike beat some of the other guys even when I am running shitty...).

This taper problem may also account for the slightly different operation in HC's carbs due to the rebuild prototype. He specifically said 'it didn't used to do that', I think in the way he has to set the screws, and also I believe he has to settle for a little more popping. Maybe Rob needs to measure a BRAND NEW set of carbs or needles to get the EXACT taper right...

WOW, GET RID OF THOSE DYNOJETS:

I have personally not been concerned about Dynojet needles wearing too much. I know of three sets of carbs with about 20k-30k on them which do not seem to be having a wear problem. The fact that replacing the stock needles and having them react so well seems to bear this out - no taper damage.

This newer problem concerns me more, and causes me to reverse my indifference to using the Dynojet needles - reason - they just don't match the carbs well enough, they are just plain wrong...

I have another thread about pilots and jet sizes I am going to post, also concerning how some people have been using the pilot sizes and screw settings to correct for Dynojet needles.

- h.