1991 FZR has spark but will only fire on the two inside cylinders?

SOURCE: I can't get my fzr 600 to start...

hey m8,, does the petrol pump work,, and fuel in the carbs,
make sure u have fuel gettin to the carbs,,pull off the fuel line on the carb, and a quick on and off of the ignition, see if fuel pours out the fuel line 1st,,if thats all cool,, then check u havent got a air leak ,in the air box,, check the jubilee clips on the carbs holdin the air box on are sealing and tight,, ,if thats cool, check and clean your plugs,, take a plug out and put in its cap again ,lay on top the motor and turn the engine over, check if its sparkin nice,, if all that is good ,, this happens a lot if been mest with,, but have u had the coil leads off b4,, if so u may have the wires on the wrong coils,, as u r sat on the bike, from left to right should be 1,3,4,2,,left coil 4 plugs 1 and 4,, right coil 4 2, and 3,,

SOURCE: yamaha fazer is miss firing

I have had the same problem. It is not the spark plugs - although it is always a ggod idea to change them to eliminater them as a potential issue.
The Spark plug holder can be a problem - in my case the wires leading from the ignition lead into the holder - had started to work loose- a common problem apparently. Solved by changing the holders.

SOURCE: very hard to start 1991 yamaha fzr 600,

Check the choke to make sure its operating correctly.

SOURCE: my 1991 yamaha fzr 600 wont start

how long did you let it sit for with gas in the carbs, you may have clogged up your jets. after awile gas will break down and turn into varnish, if your bike trys to push the varnish through the system it will clog the jets. try to take off your seat then remove your plastic over the gas tank. remove the gas tank and you will see four bowls *silver ones right next to where the gas tank is on the carbs*. your bowls are in sets of two. there are drain screws on the bowls to remove the gas inside. remove the 16 screws holding the bowl onto the carb. *4 on each* inside you will see your floats and jets. carefully loosen the jets with a screw driver then finish unscrewing them by hand, they are brass and very soft. you should be able to hold up the jets to the light and see a small pin hole. if not get some carb cleaner and give them a squirt and blow them out. do not try to use anything to clean them out, they are very very sensitive and one knick will change the jet. after that i would spray some carb cleaner up the jet holes and try to clean them out also. if you have a compressor it would be wise to use that to blow out the gunk from the jet holes as well. after you run threw all 8 jets put them back together and see how it goes, if nothing you may have to check the jets again and if clogged again your carbs are gunked up and will need to be cleaned

SOURCE: yamaha tt 250 1991 wiring diagram

Yes, but more important, needs a battery to start. After that, teh alternator provides power...if it working ok.
Wiring diagram can be found in service manual from Clymer books or from Yamaha. Meantime, goto library reference section 646 for repair/ service manuals.