Im stumped; some of this is old info. I have have a Harley Evo with a Sifton 43 cam. I took the carb apart to clean it out, new everything with a thorough cleaning. It had a 175 main and 45 slow jets and I changed to a 46 and 180. I checked the float bowl and it was good by manual specs. I put it back together and it leaked gas bad out of the overflow hose. I took it apart and cleaned the needle seat better and the leak continued, though not as bad, continued. The gas is good and nothing obstructing the needle. I thought I effed up the air/fuel seat because there was supposed to be an o-ring in there. After digging around with a pick guess what; no oring and the seat was damaged from the pick so I picked up a new carb. I went through the same procedures and back to a 45 jet with the same results. I know I have had people say go with an S&S and Mikuni but I want to figure out what the issue is. I hate giving up on something, go buy something new at 500.00 + and not figuring out what the problem was in the first place. Am I missing something?

 

Personally having had S&S and Mikuni carbs I like the CV carbs and run a Screaming Eagle CV44 on my twincam Electra Glide 88" to 103" build.
Sounds like maybe a bad float,would be odd to have the same issue with both carbs but not out of the realm of possibility.

 

Yeah, bowls good, even tried another one.

 

you've checked and replaced the needle and checked the seat so pull it off and check your float height.
Or float doesn't have a leak.

 

o-ring ?
on the mixture screw???
a hole in a metal float of a composite float that absorbs fuel could be an issue as was mentioned.
if your fuel inlet needle has the anti-vibration spring, are you setting the height with it collapsed?? it should not and if you are this maybe where the leak is from as this effects seat pressure.

 

I had to walk away for a few days. I cleaned it all again, everything in the carb is new. I put it on a bench and put gas in it to check the float and gas starting coming out the overflow. So I know there is a seat needle issue. I am going to go back and polish up the seat one more time and flush it real good and make sure nothing got on the needle. Gas is all good so IDK. Ill work on it this weekend.
I even set the float a little lean to the factory specs.

 

if you are polishing the seat, this maybe the issue as even a fine scratch will leak. are you using the tilt method???
unfortunately there is not replaceable seat unlike carbs of yester year. the surface is flat with no bevel in the hole so the rubber needle seat can seal in a narrow band which increases applied float pressure. it is possible to repair by using a bottom mill. i have repaired the chonda carbs by adding a soft seat B&S kit. i do not know if it would work on yours because of needle length, just something to think about since the soft seat can be changed.

 

I was wondering about that polishing issue. I did not use any type of abrasive polishing compound, just carb cleaner and brasso.

 

The only thing I've ever used to clean a seat is a Q tip and carb cleaner, nothing else. Never saw any real need to polish a seat with anything else. If the seat is scratched you are kinda screwed. I think you said everything is new in the carb now and it still over flows? Might be time for a new carb if it can't or hasn't been saved with a new float and needle.