Building My Own 4-1 exhaust

Per the esteemed Mr. Jeff Saunders at z1e, even with the (relatively) resrictive, fully packed "street" muffler on my new 4 to 1, I needed to re-jet....If Chopfinger wants to run "unbaffled", the need to rejet will be even more pressing...Certainly no "expert" here, :blink: but...as I understand it, 4 to ones simply "breathe" better...
More air = need for more fuel....Build it, and the jetting will come! (later!) LOL! One COULD build them intentionally super restrictive, and possibly not need to re-jet, but why go to all the trouble of fabbing something that flows like a stock part?

You want to make a custom exhaust, right? Your goal is for the look not performance. Yet, you are not sure of your true flow through this exhaust, right? I may be missing something here but my recommendation to get correct air/fuel mixture with the your new "custom" exhaust, you may need some dyno time with Air/Fuel monitoring. I know nothing of the Colortune product. It looks simple enough.

The following may be academic and common knowledge to most here but thought it worth sharing/repeating:
I do know that any exhaust change can affect the flow at the exhaust valves. The exhaust valves are the ones you need to keep from getting too hot. As air/fuel combusts it passes out the exhaust valves. If there is greater air than the system was designed for in relation to the fuel the temps increase. Even though you estimate the new exhuast with "lobster bends" could be a close match to the flow of the stock pipe, you may actually experience freer flow and therefore lean out the Air/Fuel mixture. The result could be overheated exhaust valves leading to valve distortion and eventually catastrophic engine failure(valves, pistons, & cylinder head). This type of situation when running a chromed pipe is indicated with the blue'd apperance of the header section. Not all blueing is harmful but may be an indication of higher exhaust temps due to lean A/F mixture. Did not see your choice of metal, some blue even rainbow(Titanium) with normal temps and others won't show higher temp condition(black steel). Most stock systems run lean and when owners go to aftermarket or custom exhausts without changing the Air/Fuel mixture to a richer setting it can lead to what I described above. I suggest getting some dyno time or at the very least change your carb needle settings to a slightly richer position. The only disadvantage would be lower fuel mileage but you may save your engine. Just added thoughts. Good luck with your project and please do post pics and let us know how it turns out.

Header w/stock airbox = minor jetting changes

Pod air filters = drastic jetting changes

Header & pods = most drastic jetting changes

There were aftermarket headers tuned to run very well with the stock jets, but would run a shade better with one size larger jet but not mandatory. I got one from JC Whitney back in the 80's, ran it for many years don't know who made it because it didn't have a manufacturer's name on it. One of the places that worked on my bike said it looked like a cheap version of a Kerker. The muffler was louder than stock but not deafening

I was just wanting to build it to take something like a yoshimira slip on or something like that. Im sure ill need to step up the jets for that kind of exhaust. I guess i could get a stage 2&3 dynojet kit to start with but those are kind of expensive.

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