I recently bought a 1974 CB750 with less than 7,000 miles on it (good news). It was stored in a leaky shed for about 25 years and one of the pistons is frozen in the barrel (bad news). Since I have to do some top end work anyway, I'm planning to bore the bike out to 836cc and install a new cam from Dynoman. The folks there tell me these mods will not increase horsepower by much unless I add a less restrictive exhaust. They recommend a Kerker 4 into 1 system.
I really don't want to lose the look of the 4 pipes and would rather modify the stock pipes to reduce back pressure. One suggestion was to gut the pipes and line the inside periphery with a fiberglass sleeve. The question is how to do it. Any insights on how to gut the stock pipes or other methods for reducing back pressure will be appreciated.
I should mention that the pipes on the bike are completely rusted out. I am planning on buying a new set of stock pipes, and can get either the older "300" series or the newer "341s." Since the older pipes have less back pressure, they might be a better place to start, but since I really don't know what the insides of either set of pipes look like, I have no idea if one would be easier to gut then the other or if they can be gutted at all.
