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Discussion Starter #1
21k miles...bike was running perfectly for the last few months (since I bought it) and then yesterday (7/23/2016) after a short rest stop during an afternoon ride with some friends, it became difficult to start and wouldn't idle w/o the choke being pulled out.

Then it would only idle high and would stall if I tried to put the choke back in.

Plus, there's a hissing noise around the carb (?) that sounds new and odd and may be a source or clue to the problem. I don't recall hearing this for the past few months and I've ridden it a few days a week. I can hear it over the exhaust. My wife knows that I'm the king of hearing "things" in all of our vehicles. My ears are still good and I know when something sounds off or abnormal.

Today I'm looking into it, not really knowing what I'm doing, and pulled out the air cleaner and air box to have a look around. I'm not seeing anything suspicious, but, again, I don't really know what I'm looking for.

Here's a video I took this afternoon or what's going on...
https://youtu.be/LlaPop0BYMQ

Any advice would be soooo appreciated! Thanks!
 

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Discussion Starter #3
Definitely sounds like a vacuum leak to me, too. Back of the air box and all hoses seemed to be intact.
The carb seemed to move around a bit when I poked around it. Is it supposed to be bolted down tight?

I just downloaded a service manual and I'll poke around it for a while to see what I can find. I'm mechanically inclined, but that most on cars and I don't do near the amount of maintenance these days as I used to.
 

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The carb shoud be tight and sealed! The sound is similar to sucking air in cylinders behind the carb.
Also check the pipe which connects both cylinder tops.
 

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Is it supposed to be bolted down tight?

you will need to remove the gas tank, there's 2 clamps , 1 is for holding the rubber boot to the intake manifold, and 1 for holding the carb to the rubber boot, both bolts take a 3mm allen , you want them to be snug tight, you will get a sense when they are snugged enough , on a scale of 1 to 10 with 1 being finger tight and 10 being 90 ft.-lbs of torque, give the bolts a 3.5 out of 10
 

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maybe a 2.5 cause you want them snug tight but not where the clamp twists the rubber boot
 

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after a short rest stop during an afternoon ride with some friends, it became difficult to start and wouldn't idle w/o the choke being pulled out.

that sounds like a air leak on the intake manifold, that happened to me after a long ride and the bike parts were hot then I stopped for the night and bike got cold and I think what happened is the temperature drop from hot parts to cold caused something to give or crack on the intake boot and I had a air intake leak at the rubber intake and bike would not start without the choke pulled all the way out, motor would not idle or run on the highway to home without the choke full out, I tied a shoe string around the choke knob to keep it full out to get home. I ended up finding a crack in the rubber boot and replaced it with a new one, after which bike ran fine.
 

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Discussion Starter #8
Excellent replies, everyone, thanks! It's a scorcher out here today, but I'm pulling the bike in the garage and gonna put a fan in there to try and keep cool and get this problem fixed today.
 

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Discussion Starter #10
Bingo!! We have a winner!!

Kudos to those who mentioned an air leak on the intake manifold.
Sure enough, after getting to the carb and manifold I discovered that BOTH clamps were what I would consider loose and the carb was sucking way too much air, so I tightened them both down snug-like and then reassembled and it started right away and idles as it should.

Cool beans!

Also, I watched an online video about using a ball-end allen to tighten down the clamp screws and sadly I do not have metric ball ends, BUT I do have a long metric allen that fit perfectly if I go in from the left side and move the vacuum diaphragm out of the way. Access was easy and after several 1/4 turns of the clamp screws, everything was nice and tight.

Again, thanks for the replies and the awesome assistance. :)
 

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congrats! well done
 
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