mystery vacuum line

[gentle]

My 1986 en450 is running pretty good except for a strange idling issue. The idle will sit at 1200 for awhile then drop to 800...wont stall or anything and accelerates fine...it does make slow moving a little tricky and sitting at lights it does give me a bit of anxiousness that it will stall, but other than that I would really just like to understand what is going on for curiosities sake. It doesnt seem to happen with any rhyme or reason to it...usually when i stop at a light it will idel fine for a bit and then drop and stay that way til I take off.
My bike mechanic friend says start with a vacuum test around the carb boots, he says a little leak there can cause this issue. I did the wd40 trick, spritzing around the boots and listening for a change but didnt hear anything that correlated with the spritzing.
While doing this I discovered a hose that is hanging from the silverish valve looking thing that is directly under the tank...it comes of the silver valve looking thing, heads towards the carburetor and the end is just hanging there not connected to anything...the silver thing says nippon denso asv and some numbers. What is it? Also the rubber hoses that run from this mystery valve to the top of the valve covers are slightly cracked looking.
thanks in advance for any help in identifying these parts and with the idling issue any leads there would be great.
Josh

[gentle]

I just vigured out the silver thing Im talking about is the air switch valve

[Blaine]

Sept 1, 2013 12:31:22 GMT -6 gentle said:

I just vigured out the silver thing Im talking about is the air switch valve

Do a search. Most of us remove the PAIR system.It makes things alot cleaner,& much easier to get the valve cover off to do your valve adjustments.

[gonzo]

Only problem with loosing the PAIR system is that I lost the POP POP POP on de-acceleration. I loved that sound ;-) Made me feel like Wayne Gardner!!!

[zekkfett]

Sept 9, 2013 1:05:11 GMT -6 gonzo said:

Only problem with loosing the PAIR system is that I lost the POP POP POP on de-acceleration. I loved that sound ;-) Made me feel like Wayne Gardner!!!

Funny that you say that, cuz that is one of the sounds I CAN'T stand! I can't stand bikes with new aftermarket pipes that pop! To me, it just sounds like a poorly tuned bike!

Just did the "holesaw mod" on my best friend's V-Star 650, and I was worried that he was going to get the pops on decel, but THANK GOD the IAS system on his bike hasn't caused that with more flow out the back end. Pops on decel are actually raw, unburned fuel igniting in the exhaust system after you close the throttle = less efficiency.

BTW, the bike now sounds GREAT, without being annoying/obnoxiously loud, but now has a better low end "grunt" sound to it. Getting rid of the IAS system was a suggestion I had to him, but he is satisfied with the new sound, has no pops on decel, so we're gonna let the IAS system do it's work. The word is still out on any MPG changes, as he has only run a couple tankful's of fuel since the mod, and he's been "goosing" it just to hear the new sound (as any of us would).