Topic: 1976 CB550 fuses keep blowing!

[loveliverpool]

I know this is probably redundant out there but I haven't found a straight answer.

I have a 1976 CB550K and I just swapped out the old sealed beam headlight for an H4 bulb unit. Instead of the standard 55w bulb I put in a 35w bulb. It blew a couple fuses right away but then rode fine for a couple weeks.

On a long trip this sunday it went about 60mi of hard riding and then died and blew a fuse on me at 85mph with a puff of black smoke.

I'd put new ones in and it would blow at higher rpms. I'm sure there is a simple fix to this and it's obviously caused by the new headlight, but please help as I am bikeless and stuck!

Thanks a bunch

[goldarrow]

does fuse blow with sealed beam light? i'm suspecting shorts somewhere in your wires.  where in filament of  the fuse does it blow? center or ends of fuse?

[loveliverpool]

It didn't blow with the sealed beam unit which seems like it has to do with the new headlight/35watt bulb I put in.

It blows the fuse right in the middle every time and it's usually at higher rpms (or revving up) when it goes as it would idle pretty well.

[loveliverpool]

it's the main 15amp fuse that only blows. The other two have been in there for years and are fine.

[goldarrow]

It didn't blow with the sealed beam unit which seems like it has to do with the new headlight/35watt bulb I put in.

may be you have a bad bulb?  very unlikely but could happen???

It blows the fuse right in the middle every time and it's usually at higher rpms (or revving up) when it goes as it would idle pretty well.

i was going through this pretty much the same situation, bike would idle well, but once ride off fuse blow at the first stop sign. 

[goldarrow]

it's the main 15amp fuse that only blows. The other two have been in there for years and are fine.

my fuse blew in the middle of the filament.  traced my wiring and found the shorts, right in front of my face



now no more blowing fuse

[TwoTired]

There is a difference between the fuse blow form over current and the fuse blowing from external heating.  The former blows near the center of the link and the latter parts near or under the end caps.

Shorts and grounds usually cause the over current issues.

Oxidation and/or wrong length fuses usually cause the external heating issues.