My xj 650 is not getting enough fire when I take the plugs out and set them to the motor.
I know I need to try wires but what else could cause low spark?
It's getting gas now and I rode it for the first time a few days ago,but now the plugs are fowled and the spark is weak.
Help!?

coils? ignition box? those would be two areas of concern

Start with a good solid charge on your battery, and a new set of plugs.
A weak battery is often overlooked, but is very important to the motorcycles system (especially when we're talking about XJ's)
The plug wires should be copper if still stock, and ususally cause no problems.
Check to see if 1 & 4 seem to be firing hotter than 2 & 3 or vice-versa, which could indicate a weak coil.
Check the connections to the coils including their mounting points.
good luck.

1,3,and 4 fire but it's a weak orange spark.2 does not fire at all,and hasen't since I got the bike.

its possible that the coils are bad. you can take them off and have them tested to see if they are good. might want to check the plug caps. on mine i found one cracked and it wasnt working at all. if eveything is fine, might try a junk yard for a computer

Okay,
Two should still fire when #3 does, meaning that every time 2&3 hit TDC they both fire at the same time, and they don't care if they're on intake or exhaust, so...
Unscrew your plug caps from the spark plug wires, cut off 3/4" (if there's enough wire), and screw the ends back on after verifying that the screw and post are clean inside of the spark plug end cap. There is probably a connection problem on those plug ends.
We'll get you fixed, don't give up!
Youngblood

O.k.,I'll give that a shot as well,thanks!
Meyer