Motorcycle Repair: Running issue., rubber diaphragm, gravity feed

Question
Hello, I bought a 85 VT500C a few weeks ago from a guy that said it was running last year. I took off gas tank because it had rust in it,  and took off carbs and cleaned jets(really clean inside). Ive changed plugs (plenty of spark) and oil/Filter. Tried starting it today several times. every few seconds or so it would pop (kinda like a back fire) out of the right carb(Front cylinder). Left carb(rear cylinder) was fine. checked spark plug and it had gas on it (both cylinders). After several attempts, bike finally started! ran fine, would bog down if given quick twist of throttle. When i shut bike off, checked plugs, rear fine and clean, front spark plug was really dark. cleaned front spark plugs and repeated the whole process. Same results second time around, right carb would do a back fire type thing, and bike took several attempts to start. Plugs dark again. Bike did seem to idle just fine. only would bike fire when giving it throttle.
  I have been feeding the gas through a gravity feed tube, seeing how tank is full of rust. i dont think this would cause this kind of prob. I took the carb off again, and checked it. Seem fine, no clogs.    What could be causing this problem?? Thanks.

Answer
Hi Chris,

What you've described is classic symptoms of a stuck slide.
I would take the carbs apart again and make sure the slide on the right carb. Also make sure the rubber diaphragm at the top of the slide is sealing well and has not rips or tears in it.

-Jeff