Topic: Main Fuse keeps blowing

[climbingaz]

Bike is a '78 750k

Went on a charity bike ride this weekend on the CB.  Bike ran absolutely flawlessly for the first 100 miles, then farted out on me.  Was riding down the road and out of nowhere is just died.  Coasted to the side of the road and determined it was a blown main fuse.  I had some extras with me, so I replaced it, fired the bike back up and went on down the road for another mile or so and it blew again.

This time, I took off the seat, took the headlight out of the bucket and took the gas tank off.  Replaced the fuse again, started her back up again while fiddling with just about every wire I could see or get my hands on, and nothing it did would cause the fuse to blow while the bike was running on the side of the road.

Crossed my fingers (as I was on my last fuse) and buttoned everything back up, started it again, pulled out on the road, got up to about 30mph or so and the fugger blew again.

So it only seems to blow while the bike is under load.  I can rev the hell out of the thing in neutral and it is fine.  But once I'm rolling down the road, the second I try to get up to speed, I'm dead in the water again.

ANY IDEAS?  I suck at electrical stuff. 

[Rigid]

When you reinstalled the tank and headlight you renewed the short.  I would look for bare wires in those areas.  I can't think of any circuit that the load increases enough to blow the fuse just because the bike is accelerating or running faster.  More likely, the vibration is allowing the the bare wire to contact something.

[OldSchool_IsCool]

Is the fuse blown in the middle of the reed or is it melted under a cap? 

[climbingaz]

Is the fuse blown in the middle of the reed or is it melted under a cap? 

I'm actually running one of Hondaman's new fuse blocks with the blade-type automotive fuses.  And the fuse is blowing right in the middle.  For what it's worth, I've ridden the bike for almost 1,000 miles with his fuse block and never had this problem, so I don't think it has anything to do with his fuse box.  I'm running a 15amp main if that helps.

[climbingaz]

When you reinstalled the tank and headlight you renewed the short.  I would look for bare wires in those areas.  I can't think of any circuit that the load increases enough to blow the fuse just because the bike is accelerating or running faster.  More likely, the vibration is allowing the the bare wire to contact something.

I

When you reinstalled the tank and headlight you renewed the short.  I would look for bare wires in those areas.  I can't think of any circuit that the load increases enough to blow the fuse just because the bike is accelerating or running faster.  More likely, the vibration is allowing the the bare wire to contact something.

I'm able to get the bike all put back together with the tank, side cover, seat and headlight bucket all buttoned up and it will run fine until I try to ride it down the road.  I have a feeling there is a loose wire somewhere....perhaps it is grounding from the vibration the bike experiences when running down the road?

[scottly]

Check the wiring to your taillight/brake-light.

[crazypj]

Check battery fluid level (if you have stock type 'wet' battery?)
 100miles, no problem, may have dried it out a bit so regulator is 'seeing' incorrect voltage.
 I had same problem with XS650 a few years ago, (similar charging system,EMS)
It would run for miles then blow main fuse, replace fuse and get another 5~15 miles before it blew again

[climbingaz]

Check the wiring to your taillight/brake-light.

Those were actually the very first wires that I thought to look at since I'm running the cafe tail section, but everything looked good.  I even disconnected the taillight/brake-light once and tried to ride it down the road and the fuse still blew.  And I don't have any turn signals (front or rear).

[climbingaz]

Check battery fluid level (if you have stock type 'wet' battery?)
 100miles, no problem, may have dried it out a bit so regulator is 'seeing' incorrect voltage.
 I had same problem with XS650 a few years ago, (similar charging system,EMS)
It would run for miles then blow main fuse, replace fuse and get another 5~15 miles before it blew again

That's interesting.  I'm running a cheapo $35 Walmart special and haven't looked at the fluid level in awhile.  Hmmmm......

[climbingaz]

Hard to see in the picture, but the fluid levels in all cells was just barely touching the lower line.  I filled it back up with some distilled water and put in on the charger for a bit.  Probably won't be able to take it for a test spin till tomorrow.  Fingers crossed!