OK, got an internally stock 87 FLHTC with a supertrapp 2-1 and I did the CV conversion, with an arlen ness like air cleaner set-up. Jetted the carb at 45 pilot, 165 main, xlh1200 needle, did not drill the slide. The voes is new (the old one was on its last strands of wire). Fresh 93 gas that also went in my car.

The problem: shift into 2nd and cruise at 3,000 rpm and it spits and coughs through the carb. Cruising below or above is good to go and going WOT will blow right past the 3K problem

Any thoughts?

 

Your carby is not set up right

45 pilot is unlikely to be adequate.... I know that is what many recommend, but they are just plain wrong.... 48 is ideal in most cases
I have never liked the 1200 needle.... the stock needle with a spacer works way better
165 main is a joke........ the main only comes in very late in a CV, as the needle has control most of the way.... 185 to 195 is totally ok
drill the slide # 30 number drill

I can think of numerous mods to a CV that will all help
1. Correct size pilot jet
2. Set needle to correct height(the earlier sportster needle is popular, but to my view, not the best)
3. Modify pumper stop to allow for longer stroke
4. Modify pumper rod to eliminate unwanted pumper operation
5. Polish face of slide(that faces out)
6. Chamfer leadings edges of slide guides(and slide, but be careful, as this area is thin)
7. Correct main jet(big is the go here, as the main jet in a CV does not operate until very high rpm...... relatively speaking)
8. Correct main jet air bleed(making sure the jet entry point is suitably high)
9. Correct slide port
10. Correct slide spring tension
11. Modify emulsion ports main jet tube

I know that is a lot, and you really have to know what you are doing, or else you will almost certainly wreck it(and
there are many trashed CV's out there)

best carby ever, though most who try to tell you what to do clearly have no clue at all

 

Well... if you do anything to it before you take care of the actual problem, you're gonna have one messed up CV, especially for a tour bike. (no offense to anyone) When they spit and cough, at any rpm, it's because they are getting too much air (most often in the wrong places) and not enough fuel - period.

If it's done this since install, sounds like either the diaphram didn't seat well between the cap and body, or the float level way is off. And you could have a leak at the grommet or either of the seals next to the head, though those usually affect idle, starting or a much wider rpm range.

165 is a bit lean, even for a stock cam on a 1340. 45 will work fine if the idle screw is out (usually) about 3 turns. There are approx. 45 different needles that fit the CV. HD used about 25 of those and over 6 different ones were used in Sportsters. Drilling the slide will cause it to act lean at any throttle position other than under acceleration. It will always be "hunting" to some degree and keeping a steady speed with steady throttle position will be a thing of the past and not particularly inducive to enjoyable tour bike riding.

There are a lot of things you can do (later) for a little more response, quicker warmups, better mileage, but do yourself a favor and fix the actual problem first, otherwise you'll be very unhappy with the CV setup.

 

Did you use new gaskets where the manifold bolts to the head? It might be sucking air.

 

How far did you have the carb apart?? If you or someone before you had the carb apart and put the little silver needle jet in backwards it will cause part throttle problems. It is located on top of the main jet holder/emulsion tube and sticks up into the venturi. One end is square on both the inside and outside, the other end is square on the outside and radiused on the inside. The radiused end goes in first and sticks up into the venturi for the needle to stick in. If the square end is receiving the needle the carb will not perform correctly. As previously stated by others ensure that you do not have any vacum leaks and the diaphragm is seated correctly. Hope this helps.

 

I realize that the carb isnt set-up correctly, but I had to start somewhere. All those suggestions will help once fine tuning comes into play

The thing that keeps me thinking its not an air leak is because it only does it at the 3K mark. It will happily cruise above or below. Good info about my jetting and the needles.

All seals are new

I have had many CVs apart and am not following you on that one. Maybe I always thought I had them all the way down. Dunno, but news to me

 

At any given rpm and in a "neutral" throttle posture (no accel/decel) the diaphram/slide will be close to a particular position. If there is tiny pinhole especially around the sealing lip, it can leak intermittently. Best check is to remove the slide and use a bright flashlight while gently pulling the rubber.

And this is a bit "out there" but I have seen a bad tach cause one to miss by shorting the coil at a particular RPM. Also, 3000 is about where the module will transition the timing to full advance in the absence of a signal from the VOES. You might try disconnecting the VOES at the ground (or easiest place) and see if the symptoms are identical.

One more thing I'd suggest without any changes - try pulling the enricher out maybe half or less when it's doing it and see what results. If it eliminates it, most likely an air/fuel issue. If no change at all, it could be electrical.

Again, I'm shooting in the dark and you may have one of those "ghosts" but hopefully it'll surface so you can eliminate it And wouldn't hurt to go up one on the main though it may or may not be the culprit.

 

I had tested the VOES lastnight. I should have mentioned that. It checked out fine. I did the enrichener trick (pulling out it slightly) this morning. LOL I had forgotten how much I know. HAHA Anyhow, it helped a bunch, so I spent a bit of time this morning rejetting. 48 pilot, 175 main, went with 2 turns out on the mixture and went over to a stock needle that I had from my dyna. I was pretty surprised at how long the XLH1200 needle is compared to the stocker.

Went for a ride. MUCH better. For the most part its gone. I can still feel a touch of something here or there. So, Im thinking turn the screw out a touch more and shim the needle.

BTW, I sprayed down the intake and carb seals. They check out. Ill closely look over the diaphram while I have it apart.

All my knowledge of jetting CVs on Harleys comes from messing with Sportsters. My dyna was already done when I got it. I now know there is a big difference in starting points with the two engines.

 

That's good

Really shouldn't have to shim a stock needle except for "tweaking." The 48 will work fine with the screw properly adjusted. If the carb was used, I wonder if the slide has already been drilled (?) and whether it may have a "trick" spring. And relly, messing with the slide/spring can get you some serious low end acceleration, but steady speed cruising will suffer to some degree and that may be what you're feeling. Generally it's not an outright surging but a jittery feeling like it's just not quite happy at the throttle position while any up or down on the grip makes it feel better...

But sounds like you're getting close - stay with it Think I'll dress out and go for a spin myself...

 

You know, the only two items I did not replace in the carb were the diaphram and spring. I could not, for the life of me, tell you why I would not have sprung (no pun intended) for those two items as well when I rebuilt it.

Man, too many blows to the head over the years, I guess.

Good to know about the needle not needing shimmed. Ill work with the screw and I guess buy a new diaphram and spring tomorrow.

Thanks again!!!