[mpls450]

This is related to the last post that I made about a year ago in which my fuse kept blowing on the highway when the engine was under load at 5 or 6k rpm. I chalked it up to the original fuse holder and replaced it with a new style one. That seemed to fix the issue, or so I thought.

I've been riding all day today with no issues and all of the sudden at about 65mph going up a bit of a hill, the fuse blew. I replaced it and immediately blew that one just trying to start off. I had one last fuse to test, and put it in, tapped the brakes, flipped the blinkers on and then finally revved in neutral and it blew at about 5k rpms.

Long story short, I'm waiting for my rescue truck a few hours outside of the city and browsing the forum for advice.

Since it blows under that specific circumstance, what should I be testing & checking to locate the culprit? I'm thinking there's an intermittent short somewhere that only shows up under load, but that's just my uneducated guess. Any help/direction would be appreciated.

 

[WintrSol]

Start with a Volt meter, and measure the battery Voltage from idle up to around 4k rpm. If it goes much above 14.5V, you have a regulator problem. A more modern rectifier/regulator would be a good improvement over the stock setup.

 

[tbpmusic]

First thing to do is replace the fuse entirely with an automotive circuit breaker.
A guy could go broke buying those glass fuses, and it expedites trouble shooting by 1000%.

 

[mpls450]

Well, I finally had some time to work on this issue. I ended up replacing the regulator & rectifier with a new combination unit. Rode down to the gas station and the fuse blew starting out leaving the station. So, now I'm a bit confused as to where to check next. Voltage on the battery from idle up through 4,000 rpms fluctuates from 9v to 12v. Could it be an issue with the battery? The last time the fuse blew it was when the throttle was coming down from revving (as I was measuring the voltage).

 

[mike in idaho]

Load test the battery, there may be an internal connection problem that shows up at certain vibration levels. 9-12 volts isn't all that good, you should be seeing 12 to 13.4 volts when it's running. Is the new rectifier/regulator plugged into the harness or wired direct to the battery? Wiring the negative and positive leads directly to the battery posts eliminates possible wiring issues in the main harness and it will give you a chance to add a fuse in the positive wire for more protection.

 

[WintrSol]

Only 9V to 12V? I'd suspect your meter, or measurement technique. A new regulator should peg it at ~14V at 3000rpm. If the regulator ground is poor, it could result in bad regulation, especially at higher rpm.

As to the fuse, I suspect you have a chafed wire somewhere that sometimes makes contact with the frame, and the rpm range may be a red herring. Most likely where the harness passes out of the fuel tank tunnel to the triple tree, or where it enters the handlebars. It could also be under the seat, and being pressed on by your weight shifting on the seat. Do you operate with the lights on? If so, the wiring through the rear fender could be at fault. If you can connect it blowing to an event other than just high rpm, that could narrow it down.

BTW, if you show where in the world you are located, it could help a fellow member to step up. This kind of thing is easier found hands-on.

 

[mpls450]

Bringing this back to the top as I still have not solved this issue but have a new clue. After running the bike and looking up and down for a short, wiggling wires and pushing and pulling on parts, I couldn't make the fuse blow. Then all of the sudden it blew again. Unprovoked and at idle. So, I put a new fuse in, didn't even start the bike this time and a few seconds later it blew. So, I think I can rule out a bad new regulator or anything that had to do with the bike running. Could it be a bad battery or should I keep chasing a short?

 

[Flyin900]

Start with your battery and get the battery load tested as a previous poster noted, as you may have a cell that is damaged. Also again a poster also suggested that +9 to12V isn't a good voltage measurement at idle. You should be seeing +12.5V at least at idle and 14V+ at 3000 RPM, so you have a problem with your electrical system with either the battery or the stator or rectifier being the potential culprits here. Check your wiring and grounds and the new rectifier wiring to be sure everything there is in top shape.

You can get the battery tested at any automotive parts store and usually between 200-300 cold cranking amps is a generic number to be shooting for in a spec unless you know the battery spec on yours. The stator can be tested with your ohm meter for a dead short or compromised windings and there is a spec in the service manual for that test. Hopefully the rectifier is still good and since it is new the other items should be tested first. I am not that familiar with the rotor on that bike if it is just a magnetic metal drum that rotates around the static stator, or if it too has electrical windings and if so another possible culprit to check. I know that some electrical parts can test good cold (ie) rotors and stators, yet once warm they break down and are intermittent, so you may also want to be testing these items specs at full operating temp.

 

[cb350(k5)]

If you blew the fuse without the bike running you don't have a battery or charger problem. You have a short. Keep checking. Where is hard to say but you have a short.

 

[mike in idaho]

Pull the tank and the seat off and check out the black wire. There is a branch that goes to the rear brake light switch, one under the tank that feeds the coils and horn. Also a branch feeds the turn signal flasher and the starter solenoid. Does it have a kill switch?, it may be grounded inside the handlebar, unplug the back and black/white wires from the handlebar loom and plug them together to bypass the kill switch. The black/white wire should be checked too, it runs from the headlight bucket to the coils.

 

[mpls450]

Pulled the tank, checked the wiring from the headlight to the tail light and it just doesn't seem to be anything obvious. Turned the bike on (not running) and tried to get the fuse to blow again but couldn't. I think there's something to the comment about the short happening only when the bike is at running temp. I think I'll just have to keep testing to narrow it down. Unfortunately it seems that the more I work on this, the less of an idea I have of what I could be. Are there only specific parts in the electrical system that could blow that main fuse if shorted? I'm still shooting in the dark a bit here.