Motorcycle Repair: 84 yamaha 700, exhaust gaskets, yamaha 700

Question
I just bought the bike for 400$ about two weeks ago. It didn't need anywork or so I thought. and the guy gave me a 81 yamaha 700 for parts no title or carbs. for that one.
Now the pronblem  is the with the 84. the front cylinder blows cold air out of the exhaust, and the rear cyclinder blows hot. at low speeds and keeping rpms under about 5000 he bike pops and back fires out of the front cyclinder. I am in the auto mechanics field but for cars not motorcycles and I am really lost with what it could be. I know it gets spark.  I am not sure if the carbs are out of syncro or not, or if that would even cause the problem. and advice would be most helpfull thank you. If it matters the bike has street pipes on it

Answer
Hi Mike,

From the description given, both exhaust gaskets need replaced. Seal those leaks.

The front cylinder isn't getting fuel. If that pipe even gets warm, its from compression. The carbs will need thoroughly cleaned and then synchronized. Other work may be necessary, too.

Respectfully,
Mark Shively