Interchangability of CV carbs

Are there any significant differences between older and newer CV carbs such as size or mounting? Are they all 40mm? I'm thinking of buying a newer CV carb that came off a twin-cam motor and adapting it to an early Evo. Or should I be looking for an eariler model?

They are not identical (different jetting, needle, etc.) but a 40 CV is a 40 CV & with about $15 worth of factory parts, can be set to run Harley engines made over a long period of time just fine - up to 100 HP.

I'm a Sportster guy so I can't tell you much about what the settings ought to be for any given BT, but I do know that guys with older Ironhead Sportsters get a used CV & tune it to make the bike run like a champ. Panhead, Shovelhead, etc. owners have too.

Sometimes you need a different intake manifold & throttle cables, but it's not all that difficult to put a CV on an earlier model bike & the parts to do it are readily available. For example, if you don't have a J&P Cycles catalog, get one - free for the asking. (No, I don't work for J&P).

Ok, so does this mean that twin-cam motors also came OEM with a 40mm carb? Or did they go to a 42 or 44mm? Thanks.

To the best of my knowledge & hotroadking says so too, TC's came with the 40mm carb. And you do not want to go with a larger one unless there's serious headwork, cams, etc. Yes, a larger carb will flow more on the top end, but throttle response & torque @ lower rpms will drop.

Thanks for the info. And I agree that I don't want to go larger than 40mm, which is why I was concerned about a TC carb being slightly larger since the displacement is bigger than an Evo. I'm running an old 40mm Screaming Eagle butterfly type Keihin that I've hated since the day I put it on (1989). Rather than rebuild it again I'd like to swap to something more streetable.

Most popular needle is the infamous N65C, H-D part number 27094-88. It originally came in 1988 XL1200 Sportsters. Sometimes a shim or 2 is needed (brass washers you can get for a dime @ the hardware store) but usually not.

There were only three major changes to the CVK 40 from 1989 to 2006
1989 on XL did not have an accel pump
In 1994-1995 the accel pump was redesigned
The last mod (-98?) the external venting was changed to internal venting.

I like the late model CV's because the pump is better and the vent is internal which means one less hose hanging around.

The butterfly SE was an abortion.... impossible to tune and a POS from the git go.

1988 was the 1st year for the CV40 on a Sportster & that carb is the one the needle I mentioned is for. That carb didn't have an accel pump & neither did the '89 models, but starting in 1990 they did. As CD mentioned, the pump design was modified for '95 models.

That can be a problem with some air-cleaners too & our Buell friends who like to use the "Forcewinder" air-cleaner found that out before anybody else I know of did. Had to modify the A/C slightly so the carb vent would work on several carbs.