Lean mixture in the afternoon?

First off am I correct that an engine maintaining revs after closing the throttle is an indication of a lean mixture?

My maxim does this after the highway portion of my commute most afternoons. However in the morning I do not notice the same thing when i reach the city. Colder temps in the morning should make it even more lean shouldn't it?

What gives?

 

The slides are probably sticking when the carbs are cold. Pretty common problem if the slide bores haven't been cleaned in a long while.

Search: "Clunk test" and read about the problem.

 

They tend to speed up when they get hot if too lean or you have air leaks.

 

My bike revs at about 3500 rpm after letting off the throttle then drops back to 1500 RPM after about 30 seconds. Sometimes it seems that braking will cause it to drop back sooner. This has not been proven but it seems to work that way.

 

Could be:

Air leaks. Common if the intake manifolds are deteriorating because the bike was stored out of doors for a long time.

Mixture. Also common. People mess with the settings and get the whole set out of whack.

Mechanical. Tight cabling. Sticking linkage. Dirt in pivot points and hinges.

Tuning. Carbs are aged and the vacuum pistons are sticking or not rising and falling as they should.

Other. Stuck or leaking enrichment circuit valves not seating and allowing extra fuel to enter the intakes.

 

On the limited info... it doesnt seem to be the ambient temp so much as the bike being good and hot.

Makes me wonder if there aren't some cracks in your intake causing the leaner condition?
You might try the carb cleaner or brakeleener on the intakes trick when its fully hot to see if there is any change.

Rick seems to have listed all the possibilities, if thats not it.

Just a hunch

 

I just removed and cleaned the carbs on my XJ650J ('82) although I didn't use any tools to clean gunk out of any of the small tubes or jets. Just a LOT of carb cleaner. I seem to have spark (I'm assuming that the safety relay would prevent this if it was defective) - bike is in N and on center stand with kick stand up.

My question is this - I'm waiting for some replacement cab to airbox tubes - so there is nothing blocking the intake (thunk test is ok by the way).
Will this prevent starting, or should it run even without the resistance of an air filter?

Thanks!
So far, cleaned petcock, switched to prime for a bit, replaced fuel and vacuum lines, added an inline filter..
gas might just be 'regular'.. not 93 octane...