Cb550f blowing main fuse

[Towsejames]

Hi,

I’ve finally got my 550 on the road and riding for the first time with me just in time to catch the last of summer - (since I think 1999). A lot of titivation changing and rebuilding carbs, fork seals, tubes tyres, electronic ignition, servicing and lots of cleaning up.

I am sussing out some teething issues since taking it on short journeys where I live to try and make it reliable. It has broken down on me a few times but nothing a little roadside fix and cleaning up and improving electronic connectors didn’t solve.

However my latest breakdown blew the 15a main fuse losing all electrics to the bike, luckily a spare was there which allowed me to get home - something to note is I rode the bike for about 5-10 mins with the headlights on for the first time when the fuse blew. With this in mind I rode home using only the pilot lamp which seemed to be fine, around 2 mins from my house I switched my headlight back on which lasted the 2 mins home blowing the main fuse again right outside my house. The headlight thing could be a coincidence but they do also seem abit dim even though the bike charges.

Has anyone had the main fuse blow?

My plan is to replace the fuse box for a newer blade type anyway checking for any bad connections along the way.

Thanks for any help


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[Towsejames]

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[K2-K6]

You haven't got any led bulbs in replacement for conventional items installed have you ?

Just a thought, as if there's failure on some of these they can give a resisitive short to ground, which then puts some demand in capacity on main fuse.

In other words, the headlight then looks like culprit, but it's the diminished capacity giving less headroom that causes failure.

Just a reality check, can be ignored if not present.

[Otis]

Hi,

I’ve finally got my 550 on the road and riding for the first time with me just in time to catch the last of summer - (since I think 1999). A lot of titivation changing and rebuilding carbs, fork seals, tubes tyres, electronic ignition, servicing and lots of cleaning up.

I am sussing out some teething issues since taking it on short journeys where I live to try and make it reliable. It has broken down on me a few times but nothing a little roadside fix and cleaning up and improving electronic connectors didn’t solve.

However my latest breakdown blew the 15a main fuse losing all electrics to the bike, luckily a spare was there which allowed me to get home - something to note is I rode the bike for about 5-10 mins with the headlights on for the first time when the fuse blew. With this in mind I rode home using only the pilot lamp which seemed to be fine, around 2 mins from my house I switched my headlight back on which lasted the 2 mins home blowing the main fuse again right outside my house. The headlight thing could be a coincidence but they do also seem abit dim even though the bike charges.

Has anyone had the main fuse blow?

My plan is to replace the fuse box for a newer blade type anyway checking for any bad connections along the way.

Thanks for any help


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Hi James,

I had exactly the same thing a few months back with my 350 Four and had to call the AA. The chap replaced the main fuse and suggested following me home in case it went again, well 3 miles up the road it did and he transported me home.

A week before I had replaced the bulbs in the dashboard, tacho and speedo so thought this would be the best place to start. Inside the headlight the wires are a right mess but I methodically checked each circuit and found a bad connection. Repaired the bad one and double checked the others. Put in a new fuse and all has been perfect ever since. I have to say I was somewhat surprised at how disabled the bike was with a dodgy main fuse.

Happy hunting and hope you find it uickly because it is very annoying.

Cheers

[deltarider]

Has anyone had the main fuse blow?

O, yes, over 46 years a couple of times, but not any more since I've made it a habit at the start of the season to clean the ends of the main fuse and the clips that are holding it. If these contacts are not clean or are even slightly oxidised, under circumstances the fuse will blow. Always have a spare with you but do not position it before you have carefully inspected cq cleaned its ends and the clips. The 5A (taillight) and the 7A (headlamp) are still the ones the bike got on 1976 at the assembly line.
In spite of a 60/55 Watts H4, 3 ohm coils in combination with a transistorized ignition, 15A has always served me.

[taysidedragon]

Check the connections on the back of the fuse box. They can get corroded and increase resistance, leading to blown fuses. Were your fuses old ones? The glass fuses can fail sometimes through ageing. I had one fail, the metal caps just separated from the glass.

[Johnny4428]

I also have had the exactly same thing happen to me a few times in the past. I nearly always run with headlight on and sure enough that’s enough to blow the main fuse with the extra resistance at the poor fuse connections. Easily sorted with good clean and a little bending of the tabs at the fuse ends. Going to replace with blade fuse box at some stage. Not bothered about originality behind the panel in pursuit of reliability.

[TrickyMicky]

I had this happen a couple of times on the 400. I was advised to check the multi-plug supplying the fuse holder. Sure enough, after 40 odd years all the spade connectors inside were a lovely shade of green. Did not take too long with a set of jewellers files to restore them, and no problem since. The person who told me to look there, also mentioned that with the glass fuses, if it fails with the wire broken inside the glass, then that is usually a short.  If it fails because the end cap on the fuse has parted company, as in my case, then that is because it has got hot trying to draw current through the corroded connections. 

[Bryanj]

Look at the blown fuse and is it

1 melted in the middle with visible"blobs"

2detached at one end and "floating

[Otis]

Crikey,

I had no idea there could be so many culprits!!

[Bryanj]

The answer to  my question may tell me WHY it blew and shorten the odds on culprit

[Oddjob]

Something odd here. The first pic is confusing. The tank looks like a 550K3 but the side panel badges are off a 550K0-2 not a K3. Totally different. Plus IIRC the 550F has one upper mounting lug going vertical and yours are both horizontal  The brake pedal is off a 550F, the 550K has a round tubular type. The clocks are blue faced, so either a 550F2 or a 550K3. The shape of the footrest brackets may clear it up as they are different IIRC between the 550K and the 550F. If the headlight was blowing the fuse why not the 7a fuse? try removing the headlight itself and run without it, see if it blows when the lights are on. If it doesn't suspect the lamp itself, if it does it's a wiring problem on the lighting circuit.

[Bryanj]

Looks like rh sidepanel has been "modified" to get at seat lock as well

[Otis]

Well, the OP hasn't popped in for while so I guess it is not an urgent worry.

He's certainly got enough to look into.

[3scs]

Something odd here. The first pic is confusing. The tank looks like a 550K3 but the side panel badges are off a 550K0-2 not a K3. Totally different. Plus IIRC the 550F has one upper mounting lug going vertical and yours are both horizontal  The brake pedal is off a 550F, the 550K has a round tubular type. The clocks are blue faced, so either a 550F2 or a 550K3. The shape of the footrest brackets may clear it up as they are different IIRC between the 550K and the 550F. If the headlight was blowing the fuse why not the 7a fuse? try removing the headlight itself and run without it, see if it blows when the lights are on. If it doesn't suspect the lamp itself, if it does it's a wiring problem on the lighting circuit.

it’s an F2 frame but your right it’s got some K3 bits on,the panel lugs are the same layout on both k3 and F2 on that side I think it’s the other side that’s different