Idle staying high then very slowly back down- solve (maybe)

[cutlass400]

So my bike would idle really high then gradually come down to a nice smooth idle and I couldn't figure out why. I had the carb off tunning for pod air filter and figured while I was in there to replace the slide diaphrams. When I got done the idle problem was fixed. The only other thing I did while they were off was jet it up 1 size. I don't know if the new rubber helped the slides come back down faster or maybe just centered them in the bores so they would move smother. What do you guys think?

 

[JARichmond]

If you were replacing the diaphragms, you likely fixed a lean condition (hanging RPMs). If there were visible cracks in the rubber then you would have been letting in a lot of air for a very small amount of fuel. The reason that the diaphragms must be in good condition is because the vacuum produced in the upper air chamber (above the diaphragms) pulls up your needle from its jet. When the needle is lifted, the engine vacuum pulls fuel through the open jet. If there's a hole in your diaphragm, the needle isn't moving up high enough, thereby not letting gas come through.
In short, y'done good!

 

[Drewcifer]

Please lubricate your throttle cable with some penetrating lube, not just oil. The rust needs to get removed eventually, so I'd do the following.

lift throttle cable off the carb rim below tank so you have slack.

Take the two screws out of your right grip/switch assembly
remove the cable from the nylon sleeve, slide the sleeve off.
push the cable down through the switch housing and lube the bejesus out of the cable lining.
dry lube the bar and nylon sleeve (please! Use that dry graphite stuff or if you have none, rub pencil lead over sand paper til you have a pile and dissolve it with acetone and paint it on the inside of the nylon and the bar.)
reassemble.

enjoy new silky throttle performance.

Drewcifer