I am going to buy a new exhaust system for my 1983 XJ750 Maxim to replace the rusted one on it right now. But i can’t decide weather or not to go for a the 4 into 2 or just stick with the 4 into 1 style. I recall hearing that the 4 into 2 may take away some of the bikes low end for high end. Also I fear that it may be to free flowing that I’ll have to buy a after market air box system, which I may look into, to compensate for the free flow. Also would the Mac 4 into 2 from a 650XJ work well with a XJ750?

MAC makes a 4-2-Crossover-2 and a 4-1. I beleive that MAC sells the 650 and 750 as the same part number. If you check this you'll find out for sure.


The 650 came stock with a 4-2-crossover-1. I'm pretty confident the 750 did as well. If you have a 4 into 1 then you likely don't have a stock pipe. 90% sure.


The 4 into 1 is the higher flowing pipe. If it currently has a 4 into 1 then putting another 4 into 1 onto it will not change things much. Perhaps a different manufacture might be a little diferent, and the old one might be so rusted as to be more free flowing, so a tune up wouldn't hurt.

If you change the type of system you will have to adjust the carbs accordingly. If the pipe is going to be freer flowing then generally you need to allow more gas flow through the carbs by installing a larger jet (or you will be running lean) . If the pipe is more restricted, you will need to go down jet sizes (or you will be running rich).

Cheers,
woot.

Woot,
The 650 and 750 were different. The 750 went 4-box-2, so to speak.

750 Maxim exhaust on eBay

It was not too clear from Haynes, but what I ended up discovering on my own 650 is that it came to me with a 750 exhaust. Then when I went to install the missing sidestand, it interfered and I had to cut the box apart and splice in some metal to widen it...long story; anyway, they are different, and not interchangeable.

Jim

How is that woot, that the 4 into 1 is more free flowing than the 4 into 2. I'll take your word for it but i just thought it would be logical to believe that 4 into 2 would be more free flowing? Oh yeah Jim thanks for clearing that up with interchangeability of the exhaust.

Thanks Jim - had seen a box instead of a cross over once before - wondered what that was about.

You'd think 2 pipes would be better than one, however, the stock system is the 4-2-cross over/box - 1 is the starting point. Vance and Hanes IRC correctly build a proper 4-1 pipe. The idea is that there are no sharp turns, the lengths of each downpipe are right so that pulses don't interfere with each other, and that the pipe creates a suction type of effect... basically it is a better designed pipe. It also could have a large diameter where it counts but don't quote me on that I haven't measured one personally.

What I do know is that if you go from a 4-2-crossover-1 with a 4-1 you will have to rejet... :)

I went with a MAC 4 to 2 and I'm happy with it for the most part. I left my stock air box in place and went with a stage 1 jet kit to compensate. Either way expect to do some jetting, mixture adjustment; & carb syncing. It has taken me a few tries and some anger.... but it has worked out well and I have more power & a great running bike

One of the main reasons I went with the 4 to 2 was that the 4 to 1 seemed to get in the way of the Oil filter bolt. So you would have to remove the exhaust every time you needed to change the oil filter. Otherwise you could go with the spin on oil filter to get around that problem.

The only down side that I have run into with the 4 to 2 is that the center & side stands butt right up against the exhaust when they are in the up position. The stock exhaust had a grommet to prevent that, the MACs do not. I still have not fixed that yet, looking to rig something to avoid that issue soon.