Won't idle when hot - 85 700S

[leftfield6]

Hi All, hoping someone can tell me what my next steps should be with my 85 Nighthawk S

I've had my low mileage 700s for a few months now.  Supposedly, the previous owner had the carbs cleaned and synced at a local MC shop earlier this year.  I have no receipts, just his word for that.  So here's what I'm having trouble with. 

Sometimes (maybe 50% of the time) after a run at interstate speeds, the bike doesn't want to idle.  Lets say I come off the interstate onto an exit ramp, I gear down through the gears, and come to a stop at the stoplight.  Clutch in, rpms drop to 1000+/-, for just a sec, and then kinda stumble, dropping down a few hundred, than another few, and then stalls.  Bike will immediately fire back up with a little throttle, and if I slightly crack the throttle, it will stay running, at 1000-1200 rpms.

I don't want to adjust my idle speed upward, because the 50% of the time it doesn't die, the bike idles at about 1100 rpm, although rarely exactly perfectly.  Even during one of the times that it doesn't stall, and maintains a decent idle, it always "hunts" a little bit.  1000rpm->1100rpm->1200rpm->1000rpm->1200rpm, etc, etc.

Otherwise, the bike runs great, no missing at speed, not hard to start, choke works perfectly, etc.

So far, I've ran SeaFoam through on two tankfuls, adding about 5 ounces to each tank, per the SeaFoam instructions.  No noticeable change yet.

I'd really like to have an idle I can count on, dealing with this in Atlanta traffic, with all the stop-and-go makes for a very high stress commute.  Plus I know I'm putting unnecessary wear on my starter, battery, etc.

Any suggestions on where to start?  Thanks in advance!!!

[Bad Boy]

Check the hose clamps on the carbs, make sure they are tight.  Could have vacuum leak.
Then try and set the idle speed up to 1200 and see if that keeps it running.

[ariwhiteboy]

Could the slow jets be clogged?     I'm just guessing at it.

[windrider]

Sounds like a small vacuum leak to me.  Maybe one of the slow jets in one carb has a problem, but it sounds more like something is leaking vacuum.  Have you checked the carb to head torque, and verfied all the vacuum plugs are tight from the balance operation?
Just a couple of thoughts.

[leftfield6]

Thanks for the suggestions, all.  I'll take a look at the boots, vacuum connections and plugs, etc.  I'll report back with findings. 

Hopefully it's one of these, I hope to not have to remove and disassemble the carbs. 

[leftfield6]

Been a while since I updated this thread, I've been out of town on business much of the time the last few weeks, so not much riding. 

Good news, I think this is cured!  Knock on wood, of course.  I checked all the vacuum lines I could get my hands on, and all the rubber seals and clamps, and everything seemed shipshape.  So, I took someones advice (from another thread) and did the SeaFoam treatment.  1/2 a bottle added to a full tank of gas, repeat, and you're done.  Well, I'm most of the way through the second tank (about 1/4 tank left) and I think my idle problems have gone away.  The ride home today in traffic will be the big test, I'll have enough stop and go, to get the engine good and hot, so we shall see if the idle monster rears it's head.