I have a 2000 Softail with a CV carb. I rode it to work and everything worked great. On the way home it was slow on acceleration and needed a downhill to do more than 70mph. Took the air filter off and noticed that anytime i hit the throttle (bike running) that the vacuum slide stays bottomed out. I can move it by hand and hear it making noise on the top like its making good vacuum. The other things i did was remove the bowl and removed the jets. Both were super clean and there wasn't any trash. Im not sure how much or how little that slide is supposed to move with throttle and would appreciate any help or pointed in the right direction. Thank you

 

... Seeing what the answer is. To the top.

 

Sounds like you have a pinhole in the slide diaphragm.

Since the needle is raised by the slide, if it isn't moving up as the engine RPM increases, the main jet will never open up, and you'll definitely be having fuel starvation at higher RPMs.

Cheers!

 

Replace diaphragm in the top of the carb.

 

It's a 2000 model bike with an apparent hole in the diaphragm, I would suggest it's time for a complete carb rebuild... The CV40 is actually pretty easy to rebuild and tune.

IMHO.... the Keihin CV40 carb is underrated and under appreciated... suffering from the weak reputation of its predecessor, the Keihin butterfly carb...

For parts and tips, go here... https://cv-performance.com/instructions-guides

 

I was thinking the same thing sounds like a bad diaphragm. I have a 2000 Heritage with the cv carb. I love my carb! My Heritage is big bored to a 95 ci with gear drive 37 Andrews cams and SS Super Stock heads. My cv carb is well tuned and performs very well!

 

Diaphram has a leak - Period.

 

Easiest way to check operation of a slide is to blow (low pressure, not 100psi!) air into the opening at the top and watch it raise and fall.

 

And don’t pinch the damned thing when you install the new one. Don’t ask how I know.

 

Yeah that happens a lot too. Best method I found for that is put the slide in the freezer for a while. It shrinks the rubber. Then drop it in and place the top on and slowly make a little circular motion while slightly pressing down. You'll hear and feel it snap into place.