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CV Carburetors

Replacing the CV carb's top cover

Last winter I did an R & R on my stock CV carb. It was running lean in the mid-range so thought I would monkey with the needle to enrich the mixture at that range. All went well until I got to the point of installing the top cover over the thin-as-hell rubber diaphragm. After about an hour of tediously trying to keep from pinching the diaphragm between the cover and carb body I decided there had to be a better way (a long time friend calls me an "eventual learner").

The service manual wasn't much help with, "Check to be sure diaphragm is seated evenly into groove at top of carburetor body." I Googled "cv carb diaphragm installation" to see if I could find a better description or trick to seating the top cover.

There were lots of suggestions but most regarding wiggling, buying new diaphragms, or using some sort of lubricant. With all the hits I realized this was a very common problem but with no simple cures until I found MKL's (Moshe K. Levy) site.

MKL's site describes the best process I've found for installing the diaphragm. His directions read,

"GENTLY (get the hint yet?) and very slowly move the top cover around in a large circular motion while keeping the carb body itself stationary (NO DOWNWARD PRESSURE!!!!) to seat the diaphragm. In this manner, it will seat itself perfectly - but you still need to check!"

Back out in the garage I gave it a try. Like magic, the diaphragm seated with about 15 seconds of circular motion! Just to be sure it wasn't a fluke I pulled the cover off and tried again. I had been lucky the first time. The second try took a few seconds more.

MKLSportster