Sparks fly when connecting new battery

[Sparky36]

A little background:  Bought my first motorcycle, a 1978 CB 750 about a month ago.  Its a half finished cafe build that I thought would make a great learning experience not to mention a fun new hobby.  Only problem when I bought it was that the bike wouldn't run without the choke on and the battery seemed to be on its last legs.  Oh, and there is no tachometer.  Don't worry I didn't spend much.  I took off and thoroughly cleaned the carbs.  Put them back on and after a few kicks, the bike started right up.  It was able to idle with the choke off.  There was the occasional pop while it idled and after idling for around 5 minutes the rpm's dropped and the bike stalled out.  The engine was a little hotter than I would expect.  The oil level is fine.  I waited a day, started it (required starting fluid this time) and the same thing happened although it was able to idle for about 2 minutes instead of 5.  I did some reading and it sounded like the ignition coils weren't getting enough power which made me think the battery was worse off than I suspected.

Today I bought a new battery.  The bike was off.  When I tried to hook it up, sparks flew and smoke rose from the cables before I could break the connection.  Hopefully there's no damage from that.  The wiring on this bike is a mess.  I was hoping for some tips on how to go about troubleshooting and perhaps where to start.  Thanks!

[TOOLS1]

Welcome to the forum. You probably have a short in the system somewhere. However, you should have a fuse, or breaker in the system. Look the wires over, for possible shorts. If, you do not find any, hook a test light between the battery, and ground. Then start disconnecting things until the light goes out. That will be the circuit that has the short.
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[cdaiscool]

Sheesh! I would grab the FSM and start going through the wiring. If it's smoking, where did it smoke from? If near the battery, you got a pretty decent short somewhere. You gotta fix that before your bike turns into the local 6 o'clock on-fire story!

[Sparky36]

You guys are gonna love this...

I started looking for shorts when I noticed that the positive and negative terminals on the new battery were on opposite sides of the old one.  It was a little awkward but I was able to get the cables in their proper positions.  The bike still had trouble starting.  I was able to get it to start with some starting fluid.  Still having idle troubles too.  I'll see if I can get that fixed.  If not I'll be sure to post again.  Thanks for your help, sorry for my blonde moment!

[cdaiscool]

Yay for easy fixes!

[free2ride]

Sparky36 wrote

You guys are gonna love this...

I started looking for shorts when I noticed that the positive and negative terminals on the new battery were on opposite sides of the old one.  It was a little awkward but I was able to get the cables in their proper positions.  The bike still had trouble starting.  I was able to get it to start with some starting fluid.  Still having idle troubles too.  I'll see if I can get that fixed.  If not I'll be sure to post again.  Thanks for your help, sorry for my blonde moment!

believe it or not that was my first thought [Ockham's razor]