Motorcycle Repair: jetting, honda cb, exuast

Question
I have an 1981 Honda cb 900f. I have the original exuast 4 into 2 and noticed a hole on one of the pipes on the top near the manifold. The bike started to backfire  and run a little rough after this was discovered. Is this the reason why it is backfiring?
Also, I noticed the secondary jets were only 95's. In the manual they call for 105,s. Is this corect and can you give me some advice?  

Answer
Hi Thomas,

I suspect the defective exhaust is causing the backfiring.

An exhaust system is designed to be a sealed system. Exhaust gas flow is designed to help with cylinder scavaging and optimum performance, etc... putting it briefly.

Even a thin/weak header pipe can cause tuning and performance problems as such has poor thermal conducting properties.

The pipe may be repaired in some cases. Welded to build-up material and fill holes. Check with a local shop, machinist, and/or welder. Otherwise replace the pipe.

Respectfully,
Mark Shively