Read my previous post:
*Vs. C.Viper: She is just very hard to zone. It almost feels like trying to zone a weaker version of ST Claw. The fact that she has a super jump and can somewhat alternate it using the Burning Kick is a pain in the ass for Dhalsim to say the least. Although j.MP beats many of her aerial options, including the Burning Kick in most cases, she can also “tiger knee” the Burning Kick, which creates even more problems as far as tricking you into doing the wrong anti-air attack is concerned, so she can approach you, or even punish you for whiffing something like a neutral j.MP.
Seismic Hammers, albeit very punishable and not her main focus in this match up, are still a threat, too. They remain something a Dhalsim player has to constantly watch out for.
Once she gets close, she can apply pressure, especially on Dhalsim due to a lack of an invincible move on his part. Aerial Burning Kicks and MP Thunder Knuckles are all completely safe on block. In fact, I think MK and HK Burning Kicks leave her at a frame advantage on block; the MP Thunder Knuckle does not, but it is an armor-breaking special move. Needless to say, up close she is highly dangerous as she can apply pressure and dizzy Dhalsim rather easily.
I have done my research, and I have noticed that C.Viper’s hardest match ups come from characters (even low mid tier ones, such as Honda) who can get into her face. Characters who can simply put offensive pressure on her. However, “Dhalsim” and “offensive pressure” is an oxymoron in Street Fighter IV. The fact that he is a one-dimensional characters means that he is severely crippled in some match ups in which he cannot force his style of gameplay on his opponents. My point is that ST Dhalsim had Drill Kicks and good tick throws. SFIV Dhalsim has neither, which is why his offensive game is almost non-existant, which is why, again, he struggles against characters like Viper, whom Dhalsim would probably be better of semi-rushing rather than zoning. *
Use neutral j.MP / j.HK to beat Flame Kicks when the Viper player uses it randomly. Do not bother using b+HK too much in this match up. It is worthless since she will mostly be jumping directly at your head, so stick to b+MP when you are on the ground. When she does ambiguous cross ups (and trust me they are) using Flame Kicks after knock downs, it can be really difficult to block, and there are no easy ways out as far as I know (especially since she can just super jump in and do other mix ups). Just remember to block cross ups by holding forward. Do not panic, though. If you try to force your way out, Viper can stun Dhalsim in a heartbeat.
I have no other suggestions because every time I play this match up using Dhalsim I usually lose unless I can land a lucky IAT -> j.HP -> b+MK -> LP Yoga Flame -> Yoga Inferno. Basically, Viper is immensely hard to zone - she has a super jump, good air-to-air priority, and a Flame Kick that can obviously be used in the air to change the way she lands. All of this is a disaster for Dhalsim because it screws with his anti-aerial game. To make matters worse, she also has Seismic Hammers, which do more damage than Yoga Fires, so you cannot trade with them. She can apply pressure up close easily with quick pokes into MP Thunder Knuckle (which is 100% safe on block). Eat 2-3 simple combos and you are dizzy.
She can fly around the screen. She is very fast. She can get in your face. She can dizzy you easily. With the exception of the initial tier list, I have yet to see one that does not have this match up listed as 3:7 favoring Viper.