Do i need to rejet?

I'm interested in putting a Mac 4 into 1 exhaust on my 81 750 Seca, and I'm just wondering if I would need to rejet the carbs. I'm planning on sticking with the stock-style air filter (non K&N). Seems to me that some bikes go crazy when you put a new pipe on, and others behave just fine.

I'm crossing my fingers that maybe a little tweaking of the idle mixture is all thats needed on the XJ's.

Chad

 

I would also like to get some insight on this. I was thinking about going this route with my XJ550 maxim, changing my 4 into 2, anyone have any experience with this

 

When I did a MAC 4-1 on my KZ I did have to rejet. No pods either.

 

MAC recommends a jet kit. See the bottom of this page.

You could work around it by playing with the float level, shimming the needles, and maybe a main jet adjustment...but a proper jet kit is almost plug and play.

 

Don't ever shim the needles unless you have verified that it's too lean at part throttle or you will just foul the plugs and waste gas.
Whether you need to re-jet depends on how restrictive or free flowing the new muffler is and how the bike is tuned now. You would have to install the exhaust system then tune for the correct mixture to see what jets you need, there's almost no way to predict that in advance.
A jet kit is going to just be a waste of money since it's not likely to have the jets you need unless it was configured for the exact exhaust system that is being installed.
It will come out the closest to stock when installing a muffler with the least restriction if you also install pod filters since they tend to cancel out some of the changes made by the exhaust at some RPMs but not at others.
When I installed a Supertrap stainless steel 4-1 on the Seca I had to increase the pilot jets and main jets by a size since it was a bit too lean just off idle and at full throttle but un-shim or go down with the tapered needle because it was too rich in the mid range.

 

i went with a adynojet kit when i went with a kerker pipe and ill tell you trying to dial it in was a pain in ass but worth the effort,it takes patience but you will find the sweet spot.good luck if you have problems give a type ill try to help.

 

by the way i went with kns too