Topic: CB550F 1976 Main Fuse Issue

[carago]

Hi All,

I am an absolute newbie so please excuse my ignorance - i have searched previous posts  but have not found an answer to my question.

I recently bought a 76 CB550F, it seems to be pretty original and apparently was a European model that spent most of its time stored. I believe the 17000kms to be genuine and most everything looks stock except it has double front discs and the exhaust has been replaced.

During spirited riding the main fuse blows, this has happened twice now and i really want to resolve the issue. After the first fuse blew i had a good look at the fuse box and it looks like all the fuses have been replaced with higher resistance fuses, ie. the 15A main fuse socket had a 30A fuse in it. This seems like a bit of a red flag in hindsight and i think i am up for some electrical refreshment. I replaced the 30A with a 15A and this has just blown, and the plastic around the fuse has melted. A new fuse got me back home but i can see this re-occurring until something is done.

My question is; should i replace the stock regulator/rectifier with a new 'solid state' type that seems to be a popular swap out?

Does anyone have any other tips and tricks regarding this main fuse problem? Should i try to replace the box and glass fuses with blade type items?

Thanks very much in advance, i look forward to leaning more about these great bikes.

Craig

[scottly]

A fuse is used to protect a circuit from excessive current, i.e. a "short circuit". The melting is probably due to the fact that the PO replaced the fuse with one that has twice the current rating, instead of fixing the excessive current draw.
Don't go buying parts until you identify the problem.(unless you have more money than you know what to do with  )   

[shizzomynizzo]

You probably have a loose ground connection somewhere. Check all your connections.

I had a problem with the coils not grounding enough and when getting on the throttle, it would blow the main fuse too.

good luck

[scottly]

Shorts blow fuses, "loose" connections constitute open connections. IF the open, or high resistance connection, either ground or battery, is used as the reference for the the voltage regulator, it will not function properly, but even at max output, these systems shouldn't/can't? blow fuses   

[dave500]

youll have to look for a short circuit,a wire or bunched up wires worn through the insulation,spirited riding involves the brakes a lot,look there first in the brake light circuit,the bike diving a little more than usual might have a wire rubbed through,a good visual with glasses if you need them is the first thing it might be a tiny spot .look around the head stem area,try and lift and twist the loom all over to look for melted plastic or worn through sections,pull any rubber covers over junction plugs back and look,only change the factory rectifier or regulator if yours is playing up,and you dont desire a completely original bike,i like the electronic type.

[TwoTired]

The fuse melting issue has been covered many many times in this forum.  And I'm kind of surprised at all the diffused advice away from the real root of the problem.

Also surprised a simple search didn't find you this:
http://forums.sohc4.net/index.php?topic=2206.msg15960#msg15960

In summary, if the fuse box plastic is melted so the clips can't self align to make full, broad contact with the fuse, you'll have to replace it.

If the fuse is "blowing" under the end caps, is it unlikely to be from an actual over current condition.  Rather, it is from fuse clip corrosion heating and the heat being conducted into the fuse.

[dave500]

high resistance ,,it still wouldnt hurt to give the loom a good look at,its mostly just there and gets zero attention,and its very old,how do you know its ok?because i looked.

[scottly]

Two tired, I have been amazed at all the diffused advice on just about every topic I've seen since I found this site. My experience has taught me that to fix a problem, you must first correctly identify the "root" of the problem.
(Ex tech support engineer, did some duty in the Silicon Gulch in the early '80s 
Scott 

[carago]

Hi All

A quick Update:

I took the bike to a local tuning guru here in Brisbane Aus (Retro Motorcycles in Ormiston) and he diagnosed a worn out regulator/rectifier. The main fuse was drawing in excess of 15.5V.

I sourced a new electronic regulator rectifier: http://www.motorcycle-parts.com.au/XRR24.jpg and this was fitted and now a constant 13.8 is running through the main fuse. He rewired the fuse box to use the spare 15A slot for the main fuse and so far all is well. He took if for a 1/2hr fang and my ride back home was about 45mins of mixed highway and suburban roads and no issues; it felt like it ran much better than before and i was much more comfortable at highway speeds without the thought of break-down in the back of my mind.

Thanks for your input

[scottly]

Thanks for the feedback; it's always gratifying and educational to hear of a problem solved, especially with details. One lesson learned is to measure what you can, before guessing.

PS, could you please translate "1/2hr fang"?   

[carago]

  my apologies, fang is Australian slang for fast ride; as in "I came fanging round the corner and almost lost it..." or "Fang it mate we have to get to the bottle-o and back before half time finishes"