Topic: wtf? fusebox melted!?

[osnomad]

I FINALLY got the carbs on my 77 cb550k working well enough to run the bike for more tha a minute and almost well enough to take the bike for a ride but now something else went down. The bike was running for a few minutes when I started to smell burning plastic then it just shut off with no electrics. I figured a fuse blew but when i took the cover off all the fuses are still good and all are the correct ampearage. BUT the main 15a fuse clips melted thru the plastic housing. I let the box cool off then put the same 15a main fuse back in and it started back up but it got too hot to touch within a few seconds. all the wiring on the bike seems to be orignal and it all looks to be in pretty good shape. all the connectors are clean and clipped in properly. There doesn't seem to be anything out of the ordinary. Anyone have an idea of what might be going on? Possibly from experiencing the same issue. I've had the bike running a number of times (although, admittedly this is the longest time i have had it running straight) and this is the first time this has happened.

[MRieck]

If fluid in the battery is low it will do that. the battery begins to function as a very large resistor. Other than that a ground is very bad etc.

[Kile]

I've got a '78 K, and was having similar problems.  Fusebox didn't actually melt, but would lose all electrics, pull the side-cover off to see which fuse was blown, and burn my hands on the fusebox when I go to pull the 15a fuse.  The bike had been running fine for months before this started happening - and it happened a few times before I finally took it into a local mechanic.

Turns out it was the electronic ignition.  It was an old Dyna III that was installed years ago.  Never had any problems with it.  He would start the bike with the ignition - fuse box got too hot to touch.  Disconnected the ignition, fuse box cooled right down.

Replaced the ignition with a new Dyna S - No more problems!

Hope that helps!

- Kile

[cben750f0]

i have a '77 F1 that did the same thing... checked all my earths and replaced the fuse box with a blade type cos i couldnt get an original one, at a decent price..

peace

[TwoTired]

The fuse clips and the fuse metalic ends oxidize over time.  The oxidation is resistive and when current passes through it, heat is generated.  If you keep the fuse clips polished and bright and shiny, the contact resistance is minimized as well as the heating.  The fuse itself will heat some when current nearing it's capacity is passed through it.  Added fuse clip heating can melt the plastic.

Problem is, once the clips heats enough to melt the plastic, the clips embed themselves into it, and they are no longer able to float and align themselves so they make full conact along the width of the fuse contact.  Forcing currents through a tiny path also creates high heat. Just like using too small a wire would be.  I've seen fuse blocks get hot enough to melt the solder on the wires attached to the back of the fuse block.  While the wire still makes contact with the connecting lug, again the contact area is reduced and heating occurs at the narrowed current path.  Depending on the severity of the melted area, the fuse clips may be restored to floating/ self aligning condition, the clips may be polished and all oxidation removed, and the backside wire resoldered (carefully not the melt the plastic further) and the block can then be restored to proper operation.  Or, you can rewire the block so one of the spare positions become the main (polish the clips).  Or, replace the fuse block with a new one.

Have you added any extra elecrical load to the bike, like brighter lighting?  Extra loads, draw more current through the main fuse.  And, the closer you draw current to the fuse rating the hotter it will get.
When all is well, you should be able hold your thumb on the fuse and clips without discomfort.  If not, you have some kind of contact resistance problem.

[oldbiker]

It is also possible to have a fuse which although still continuous is faulty and generating a lot of heat. It's worth trying a new fuse, they cost only pennies.

[osnomad]

Thanks for all the suggestions so far!

The first thing i tried was a new fuse. It got hot to the point of being untouchable within only a few seconds.

The battery is brand new and right at the upper fill line.

The bike's not using an electronic ignition. Still running points.

While working on the bike I have had the head and taillight fuses out of the box so I dont run down the battery. So they are not drawing any extra current even if they weren't original. (I'm not sure that the headlight is the original wattage but it shouldn't matter with the fuse pulled)

The fuse clips are all shiny and clean. As are the fuse's contacts themselves. The clips still have some wiggle room even after melting the housing but the solder melted out of one side of the contact. There really appears to be nothing wrong anywhere but I know there must be something stupid I'm missing.

I would assume that the wire to the fusebox would also get hot if there were some kind of abnormal load on the electronics but that doesn't seem to be the case.

[spaceboy412]

I too am having this problem with my 78550k and have done the same as Osnomad, could the coils or something like that be causing the problems.

[TwoTired]

One thing I forgot to mention is that the fuse clips can lose their spring tension and not clamp onto the fuse very hard.  The low contact pressure can also cause heating.  If the metal hasn't lost its temper from being heated, you can sometimes bend the tips together.  Sometimes the clips break near the base.  It should be very difficult to remove the fuse.  If you can pull it out with your bare fingers, it's not grabbing hard enough.

[eldar]

I think tired is hitting the problem. There is either too much load or very poor connections causing high resistance. Unfortuneatly this is not always an easy problem to correct. One thing to do though is when you have made sure you have a good fuse connection, is to use so light grease such as a dielectric grease to coat the fuse ends with to help prevent corrosion. Put the fuse in and make sure it has good connection then lightly dab the grease on. Will help protect from elements that could cause corrosion and thus poor connections.

[Kile]

I'd like to recant my above post (or at least provide an update):

I've had the bike running fine for two weeks now after having replaced the electronic ignition (which fixed this problem the first time).  No problems whatsoever.

I went out to hop on the bike this morning, and it was really hard starting, acting like it was only running on half the cylinders - just like it was before I had the ignition replaced.  It wouldn't idle worth a damn (usually it starts right up and idles great with the choke on, even when it's cold).  After a minute or two of playing with the choke and throttle, it died. Continues to turn over, but won't stay running for more than 15-20 seconds.  On a whim, I took the side cover off and checked the fuse box.  Sure enough - all fuses are in good shape, but the 15a fuse burnt my finger when I touched it.  After I let it cool down and took the 15a fuse out, the fuse box was melted around the right hand side of that fuse bracket.

I too have checked the various other suggestions in this post: Battery charged & water level topped off, fuse box spring tension feels good, no corrosion in the fuse box or on the fuses.

So now not only is my bike not running again, I've got a second $250 electronic ignition that I probably didn't need to buy.  *sigh*  I think I'm going to look into the modified fuse box like cben750f1 suggested.

So I'm with osnomad now: "WTF?!?!"

It's ironic that my bike was fine until I read this thread...

- Kile

[TwoTired]

This is simple physics.  Heating with current flow is done with resistive elements.  Small contact areas are restrictive/resistive.  Current draw is determined by the load.  But, the current paths can waste energy on the way to the load device.

If your fuse holder is melting, you have contact contamination, contact area restriction, or contact pressure issues, either with the holders or with the wiring behind.  If you can't correct this, new replacement is indicated.  But, I have corrected a few of these without replacement.  It depends on how badly the plastic has melted, usually.

Sometimes the oxidation is transparent.

Good Luck!

[osnomad]

TwoTired- you were absolutely correct. Even though the contacts LOOKED clean I pulled them out and cleaned them with some sandpaper and resoldered the lead that melted. It seems to be fine after that. The box wasn't melted too badly so I was able to save it.

[Kile]

Ok - simple physics - that explains it.  I failed Physics three times...

I dusted off the Dremel and wire-wheeled all of the fusebox contacts.  Wiped all the fuses, reassembled everything and fired 'er up.  It's still not running right, but I kept touching the fuse box and it is definately NOT getting warm any more.

On to problem #2,  (Let me know if this needs a new thread).  It is sputtering and not wanting to start/idle because it's only running on two cylinders now.  I unplugged plug wires 2 &3 and there is absolutely no difference.  Plug those back in, and unlpug 1 & 4 and the bike won't start.  2 & 3 are on the same coil, so I figure maybe it's the coil.  Fortunately, I have a spare set.  Throw them on - no difference.

So maybe it's not the coils.  Back to the ignition?  It's brand new - and worked great for 2 weeks.  Could the problem above with the heat in the fuse box have fried the electronic ignition?  Is there any way I can test (short of buying another ignition )?

Thanks for the advice!

- Kile

[cben750f0]

put the points back on... that will get you back to the start... a bench mark if you will... then work from there... that way you can say either way if its the coils or some wireing to the coils from the points, or a power problem... just my thought... peace

[Kile]

Unfortunately, I don't have the original points plate.  Not sure what my dad did with it when he put the first EI on.

After my last post, I was digging through my receipts/etc. and found the instructions for the Dyna S I've got on now.  In the troubleshooting section it describes how to determine whether the ignition or coil is bad when two cylinders go out.  It's pretty straightforward - pull the plugs and lay them on the cylynder head, reverse the ignition output wires and see if the sparks transfer to the opposite plugs.  If the sparks transfer to the opposite plugs, the ignition is bad, if they don't then it's the coil or a problem somewhere in the wiring.

I'll try tomorrow after work and post results.

Thanks!

- Kile

[nteek754]

Osn
hey here is an idea as long as you dont have some major wiring trouble and that is to take your stock fuse box out and cut the  box right off of the wirs cutting them in differant lengths to identify them later when you put breakers back on I have had this on my 750 K3 for years  your local bike shop should have theses breakers in stock  uhhumm harley uses thib set up I even found the breakers at a truck stop  they have two post with tiny nuts you just put a clip on the end and bolt them on I did cover mine with electrical tape good luck Craig

[Kile]

Bummer -  reversed the ignition output wires and the sparks transfered to #2 & #3, (along with a loud backfire when I attempted to turn it over).  So, based on the information in the EI instructions, this indicates the EI is now bad.

I guess the question now is, did what was causing the fusebox to heat and melt cause both ignitions to go bad?  If it was corrosion on the fuse contacts, would that have fried the EI?  If not, what else could it be?

I think I'll go find a points plate to replace the EI, but if something's causing the EI's to burn up, how's it going to affect the points plate?

- Kile

[Glenn Stauffer]

Hey, cben750f1, care to share what the part number is on that blad fuse housing you installed?  I think it would be great info for the FAQ.  Eventually, it is better to replace the whole unit with modern fuses.  For the longest time, I kept losing the main fuse on my 550.  The fuse never blew - the solder melted out of the upper end cap.  Several times when I was on busy roads which required a quick coast to the shoulder.  Fortunately never at night or I might not be writing this.  Cleaned up the fuse contacts and the main stopped melting.  Eventually, though, these things just plain wear out and you are better off replacing the fuse block.

--Glenn

[cben750f0]

i bought it at a place in australia they call autobarn... will nip in there tomorrow and get the name and number of the part and get back to you... peace

[gkw120649]

I have a point plate with points that I used for one season.  I replaced it with a DYNA-S.  Where are you located.

[Kile]

I'm in Redding, CA (USA).  There are two points plates on Ebay right now for a '78 CB750K.  One used for $10, and one new (rebuild) for ~$40.  I think I'm going to snag one of those to play with.  A fellow I work with has a '77 CB750F and has offered to let me "borrow" his points plate, but if there's something wrong with my bike I'd be afraid of ruining somebody else's stuff.

Dynatech has a one year warranty, so I'm going to see if they'll cover mine.  (It's less than 1 month old).  However, if something in my bike screwed it up I don't expect they'll replace it (nor do I expect they should have to...)

I'd suggest hanging on to that plate just in case something happens to the EI.  I have heard people say they're zero maintenance and last forever, but when something goes wrong with them, they're out of commission.

Thanks though!

- Kile

[Japbikemike]

After mine melted on a '78 CB 750F(3) I got a spare from a bike salvage yard that arrived in a similar melted condition.  I replaced the assembly with a Kawasaki fuse block, no heating, no melting two years later.

[Hondamatic]

All of this sounds so familiar...? I have a 1977 cb750a Hondamatic that when bought had fried points and so I upgraded to the Dyna ds1-2 ignition. Also new Dyna Dc1-1 coils (3ohm). Bike ran GREAT for a couple of weeks commuting 28mi each way to work and back. One night last week while on my ride home from work, the main fuse blew on me. Scared the bejeses out of me, 65mph on a dark hwy. and POOF, no headlight and engine died. Well, managed to live thru it and replaced the blown fuse (end of fuse was melted loose and came apart when pulled out). Proceeded to ride the remaining 5mi home without blowing again. Next morning in the daylight, found fuse clip melting plastic at one end as described earlier in thread. Decided to replace old style fuses with new blade type and did so. The problem that I have is that even though the fuse doesn't blow now (20amp,..at least not yet!) , the bikes wiring harness gets hot on the bike-side of the fuse box connector. Feels warm at idle and gets almost too hot to touch at 3,000 rpm? Checked current draw at main fuse with headlight & Tail fuses removed and approx. 8amps at idle and 13.6 at 3,500rpm. Checked and cleaned ground at coil mount bolt. Battery fluid level is normal. Voltage at battery at idle 12.2 volts 13.8 at 3,000rpm. WTF?, I'm concerned that if I ride the bike like this that the harness will at some point flare up like a Coronal Mass Ejection from the Sun? Any advice would be appreciated, thx...

[TwoTired]

As mentioned earlier in this thread, heat is generated when current passes through resistive elements. If the connector contacts are corroded, the current passing through them generates heat.  Copper is a conductor of heat. So, wires near the heat source heat up. Clean the contacts of the connector.  If you can feel along the harness and find where it is hottest, you have found the restriction, and probably the location of the corrosion.  Clean it off with abrasives and give connection points a coat of dielectric grease, or, a product called Deoxit.
Cheers,