Rectifier getting very hot - 1994 Honda CBR 900 RR Fireblade

Sounds like the source of your problem is the earthing of the rectifier.

Unbolt it and clean the frame and bolt holes on the frame, also the bolts.. Rectifiers generally are earthed to the frame and if not earthed properly will cause bad running, none charging and a very very hot rectifier...

Check your carberutor - make sure you have the proper air fuel mixture - running too lean (without enough actual gasoline) will cause the bike to run hot - but even more common than that is an ignition issue - either a bad plug, rectifier, coil etc. something not giving the proper spark or something with your cdi - best to check the plug, then power coming from coil, check rectifier, your timing could be off as well - but i've seen the lean issue and iginition electrical issue be the main causes of an engine running super hot like that.

be aware the set uses two grounds, one hot and one a earth ground and if you are measuring from the wrong ground you get wrong readings.

do the self check the set has to see if you have a error code.

normal for voltage to increase with RPM, normal for voltage to decrease as battery reaches fully charged. make sure connectors are clean and tight.

chec wires for corrosion or resistence--other parts of system may need test too--things cud be failin--get a repair manual--haynes or clymer--may not be a good rectifer-is it aftermarket

The rectifiers will get hot as they rectify the AC current into DC current to charge the battery, similar to any battery charger, They often have cooling fins to help cool them, and can sometimes get hot enough to burn your hand,
If they get to hot it is because they are beginning to self destruct, and can melt all the resin out of them, which is obviously time to buy a new one.
Put a multi meter across the battery terminals, should show 12v aprox-engine stopped, 14v aprox- engine running, this will show its working.

Not always necessary to change the regulator/rectifier. Check all connections to make sure they are clean, use a good contact cleaner and finish off with dielectric grease on your electrical connections.
When some bikes get a few years on them the connections get dirty. Check to see if there are any burned or discolored wires anywhere around the regulator. The FIX on some bikes is to cut the connector completely out and solder the wires together and either seal them with heat shrink of a good electrical tape. Loose or bad connections get hot. As long as the regulator and rectifier are working there is no need to replace them if the connections are good.
Ride Safely, Ed

replace the rectifier as its breaking down under load
Cheers rob

I'm just going to run it hot and see what happens.
Wish me luck.

Stu.

your voltage/reg. can be tested in a couple different ways check ground res. check res. then revs. bias on diodes you have ac in dc out it sounds like you may have a diode gone bad allowing ac curent to flow causing the wires to get hot