Motorcycle Repair: Kerker exhaust, kawasaki kz550, air fuel mixture

Question
Hi Mark,
One of my bikes is a 1980 Kawasaki KZ550 A1. I recently found (on ebay) and purchased a 4 into 1 Kerker exhaust system. Mounting it was no problem, but when I first started it up, it was backfiring quite a bit through the exhaust. I know that this is usually due to the headpipes not being seated properly, so I loosened everything and did my best to reseat them. While the bike runs better, I am still getting some backfiring, and I am able to detect some leakage, especially around the #1 headpipe. Here are my questions:
1. Would it help to double up on the copper exhaust gaskets?
2. I was thinking of raising the carb needles by one notch. What do you think?
3. I was also thinking about going up a size or two on the main jet. What do you think?

By the way, I had dropped an e-mail to Kerker (now owned by Super-Trapp) with these questions and never received a reply. Any insight you might have would be greatly appreciated.

Thanks!
Frank Reich  

Answer
Hi Frank,

I suspect the carburetors will need some tuning to cure backfiring. Too lean air-fuel mixture causes backfiring. If it is "coughing" due to a leaky seal, then replace gaskets. Use only new, un-used exhaust gaskets. Backfiring is a air-fuel mix issue. Machining tolerances and allignment of header to exhaust ports ensure very good fit, and would not cause the problem. Check for old gaskets stuck to exhaust manifold areas.

Q: Would it help to double up on the copper exhaust gaskets?
A: No. Avoid this.

Q: I was thinking of raising the carb needles by one notch. What do you think?
A: Try adjusting air-fuel screws out or richer in 1/2 turn incriments. If problem persists, consider raising the jet needles a notch. Check valve cleartances and then synchronize carbs to finish. If either is not within specs, tuning will be fruitless.

A: I was also thinking about going up a size or two on the main jet. What do you think?
Q: Hold-off on this. I think the tuning is in lower ranges of throttle positioning. Main Jet is for 3/4 to WFO ranges. You can change mains later, if necessary. Make carb tuning changes one step at a time to know what effect the changes made. Enjoy your holiday weekend!

Respectfully,
Mark Shively