"96 CBR1000F, Vance and Hines 4-1, K@N, possibly jetted but not sure, 15K on the bike just bought. The bike runs fine, starts quick and idles right down off of choke. When I'm chopping the throttle I'll get a rapid popping noise out the back, not really a backfire. It lasts 2-3 seconds. Am I running lean/rich, or is this normal and I should just ride it and enjoy. I'm trying to put off taking it in for service it might not need. The bike is clean and otherwise cherry. Thanks.

 

Sounds like it running to rich, time to get the carbs adjusted or properly jetted.

 

Don't know what you mean by chopping the throttle but if its going on and off a lot and using quick open throttle movements followed with sharp shut offs, its normal, as the engine is unable to use the fuel your hand position is providing for the speed the bike is traveling. Think of rally cars and touring cars, they do this constantly cos the driver is on and off the throttle using it to steer the car but because the extra fuel is being supplied at low speeds the only chance the engine gets to burn it is inside the exhaust. Hence the mini explosions.

If its just doing this in normal riding its overfuelling.

 

Popping when you let off the throttle is usually due to running lean. Your pilot jets are probably slightly to small or need to be cleaned. Lean is fast but it also burns valves. If it is popping everytime you let off the throttle I would try cleaning the carbs and sync them. If that doesn't fix it go up one size on your pilot jets. But if this is only a rare occurence I wouldn't worry about it.