Before removing the washers, with the motor up to operating temps, air filter removed as in your photos, see if any fuel bubbles out at the needle. and at idle. Are you sure the needle holder is not upside down? Maybe long shots but 31-33mpg is not right.

 

It's the 2 washers under the needle.

 

I haven't got to mess much with the plug checking. But I did confirm that the needle holder is "bevel side up". (I have installed that wrong before....learned my lesson). I also had removed the washers before I saw the post about checking for fuel bubbling out. I can still check for that though.

Also the needle I put in this carb is an N8EA (27406-00), which is the stock needle for a 2000 FLHTCU, from what I researched. I got the carb used, rebuilt from a bike shop, and the needle that was in it was an N9EY (2807-04). I probably didn't need to change the needle, but since I was going to the work of getting this carb setup properly for my bike, I thought I'd change it. I figured the N9EY had some "leaner" tapers machined into the needle, than the N8EA.

 

Here's a video of the carb running. It's a slo-mo video off of an iphone. I wonder if I've got the accelerator pump aimed incorrectly.

 

I think you are right about the 9EY being a leaner needle. I don't have a chart for the CV40 needles but have attached the chart for the CV44 needles which bears out that the N8EA is probably the richest needle for the CV40 and the N9EY probably the leanest. I say this based on the N8EN being the richest needle for the CV44 and the N9ED being the leanest. Speculation on my part but it makes sense. You might want to put try the N9EY for ***** and giggles just to see what happens. CV needles are hard to come by these days but if you can get your hands on any of the needles between the N8EA and the N9EY, I would grab them. Might also consider picking up the CV "velocity" needle from CV Performance. I experimented with a Yost kit in my CV44; that needle had notches and a clip to raise and lower the needle but I could never get the carb tuned. Tossed the Yost kit and tried several HD needles and ended up with N8EL in my all bore 107" motor before being happy with the tune. That motor made 124TQ/110HP; started easy but had to use the enrichener and ran without hiccups, coughing or any of the maladies that often accompany carbureted modified performance motors.

 

Sorry, you see me pull away for a second in the video. The carb farted in my face and I crapped my pants for a second....

 

It's you exhaust system.

 

The exhaust is a SE performance II

https://supertrapp.com/shop-products...twin-se-series

 

Yeah. I saw that. I should have said it's your whole exhaust.

Look at the spit back, It's on mainly one cylinder. You might have problems with your motor, but the more open exhaust and stock header could be the issue. Try plugging your left exhaust pipe.

 

I plugged the left side baffle with a couple rags and took another video. It looks like the spit back is about the same?

So with EFI this wasn't a problem I'm sure, with how the injectors are so close to the intake. I don't recall having this much of a problem when I switched to the carb a couple years ago. I would get some oil leaking out the A/F due to the breathers but it may have also been some fuel and I didn't notice. I really noticed when I put the Andrews 21 cams in. Would that have amplified the spit-back problem if it did exist already?

If I don't have a properly tuned exhaust that mates well with the carb/intake/cam combination, I'm not sure where to start.

Or if it is something wrong with the motor, I wouldn't know what to check next. The compression and leak-down tests checked out OK. Maybe I should open up the cam chest again to make sure I didn't miss some step in changing the cams..... Like if I somehow was off a tooth on the cam chain when lining up the marks, the bike wouldn't even run right, correct? I mean, worse than it is.