82' Maxim Rejetting for 2 into 1 Exhaust

[OopsAboutThat]

Hey all, I'm looking to put a Mac 2 -1 exhaust system on my 82' Maxim. I will be sticking with the air box as opposed to pod filters and since the Maxim's main jets are different sizes stock (117.5 and 127.5), I was wondering if I am going to need to re-jet, and if so what size(s) would I have to use? I tried using the search function and all I found was jetting for pod filters. Thanks!

 

[Lou Ranger]

Before buying new parts on spec, what does the manufacturer of the 2-1 suggest will be the standard adjustment going from original to their system?
If you are lucky, maybe the replacement will be close to original spec and you won't need to re-jet.

But if they don't have a conversion formula for you, since you are only making a change to one variable it ought to be easy to immediately identify where to make an adjustment if one is required by the way it runs.

 

[16VGTIDave]

You will have to re-jet for the exhaust change. There is no magic formula for re-jetting! The guys on eBay selling "tuned" kits are scam artists. There are guesses that should get one close, but each engine is different and will have to be tested and adjusted for optimum performance and reliability.

As a starting point, increase the main jets 2 sizes larger. Then follow the testing and tuning procedure detailed here. If this process is too complicated for you (it isn't), don't change the exhaust. Or resign yourself to paying a shop 4 or 5 hours labour (minimum) to do it for you. Jets are cheap, running lean is expensive when you melt a hole in a piston...

 

[TimmyT]

You can turn pilot screws out 4 turns before needing to go up one pilot jet size. You can also raise the needle height one clip position or if your needles don't have clip positions you can use washers to raise it up and richen or lower to lean. Carb sync will play a role here and your altitude is a factor as well.

These bikes run pretty lean... even the service manual suggests tuning for lean setup. Now we have ethanol in our fuel as well to keep in mind. Regardless anytime air filters or exhaust or both are changed from stock setup, carb tuning will become a big factor including re-jetting.

Ive changed my mains from 135 to 142.5 for pods and Harley FX pipes, raised the needle one step pilot screws are out 3 1/4 turns and pilot jets are stock 42.5 ... I may need to up the pilots to 45 at some point but I still have 3/4 of a turn on the pilots before biting that bullet. Keeping filters stock will allow you to richen the mixture in much smaller increments. When you purchase jets make it worth your while and get several sizes to TRY out. Haha Dave is dead on ... if you order one of those tuned kits they are going to send you several jet sizes as well, cause they don't know either!