You're opening up a real can of worms there buddy.
You see, your FZR750 is a 2LM model, right? The Japanese domestic model, restricted to 77BHP?
So, the exhaust is part of the derestriction. It's got more twists and turns than a Tarantino script... You put another exhaust on it from a different bike and it'll have your bike running really lean - you'll know it because about 6-7000 rpm you'll get it pinking (that nasty ball bearings in a tin drum-like sound) which isn't good for it.
Best bet for you if you're going to change the exhaust and you have to put in a less restrictive one is to make a few alts at the same time.
There's a restricting plug in the airbox. It's in the air inlet - a long rubber bung which is held in with a huge metal clip. You get to the airbox by taking off the tank. Pull it off and junk it.
Next step is to get some bigger jets in the carbs. Undo the carbs at the joints to the inlet manifold (more metal clips) and pull the float bowl cover off (one at a time!). Replace the 80 mains on the inner cylinders with 105's and the 82.5 mains on the outer cylinders with 107.5s. You won't ned to change the float levels, but depending on how easily it idles and revs up you may want to take the pilot airs up to maybe 115s.
This will take care of the leaning problem, and also give you a decent horsepower increase.
The only other step in the puzzle if you wish to continue further, is to swap out the 2LM ignitor with either the 2NK ignitor from the FZR750R (1987 US model) or the 1FM ignitor from the FZR1000 (87/88 model). This will remap the ignition so that it gives you more advance and will liberate even more power.
Even if you don't do the ignitor, the derestricting will bring the bike up a good 20HP.
Good luck. It's really not hard to do at all.
And I to my motorcycle parked like the soul of the junkyard. Restored, a bicycle fleshed with power, and tore off. Up Highway 106 continually drunk on the wind in my mouth. Wringing the handlebar for speed, wild to be wreckage forever.
- James Dickey, Cherrylog Road.
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