I'm new to this site,but I have seen some great info posted here. I also need some trouble shooting advise. I have a modifided 80" pan. I am trying a cv carb,because most of my riding is between 5000 and 10,000 ft. I was told these would be good for altitude compensation. The carb I started with is off a 96 1200 sportster. I put a softer spring and tapered needle from a kit made by cc rider. I used a 45 pilot and a 170 main. the needle has three gooves and the clip is in the lowest groove. I just put it on last week and it seemed to be ok. I headed out this week end on a 1000 mile trip. The carb seemed ok at speeds 55 or lower and in slight pull. Trying to throttle above 55 or pull up hill the engine would buck and flat quit,like it was out of gas.I have a pingle petcock and drained all the gas to look at the screen and hope for just a bad tank of gas. I also loosened the cap to make sure it wasn't the vent.Sorry for a long post but I am not familer with these carbs and need help. Thanks.

 

Make sure your float is adjusted properly. You might need to step up the main jet a little also.

 

I have a feeling that the carb off the sportster is too small. You might try to get a carb off an Evo Superglide or something like that, if your at that high of an altitude you need to get alot more air in with the fuel. I would be looking for a carb of an 88 inch motor instead of one off a 74 inch. The 88 motor should have a 40 or 42 mm CV carb, the reason you seam to be running out of gas at over 5000 FT is you are probibly running into a too rich condition because of the thin air and the motor is getting choked down from lack of air. My .02

 

Pull your plugs under the condition you have the problem and see if your running rich or lean.
I had a sporty once, a 72 that i rode to the west coast on a few times and soon as i got up in the mountains it would run lean. Had to run the choke half on to keep her running, was running a Bendix carb.
I may be wrong and i have yet found a full and correct answer about it but it has been my experience that the less air moving through the carb equals less fuel.
Fuel is drawn up from the float bowl by the velocity of the air passing by the fuel ports, less air less fuel.
Thoughts ?

After thinking about it i`m prob. way off base, i have never ran a cv carb so don`t know much about them. Most my bikes have been old iron with a Bendix, whole different setup.
I am still interested in opinions about what i said, and still think you should pull your plugs to see exactly what`s going on.