Won’t Crank

[jp9094]

Have just put 350 miles on the 83 LS over the last 7 days.  Last 100 in the last 2 1/2 hours. After a short rest went to move it and only got a minimal crank when engaging the starter. Unhooked the battery and took it to local auto shop who tested it. Checked out “good” 12.7 volts. Any ideas or thoughts would be appreciated!

Thanks in advance

[Bob_Roller]

How old is the battery ??
Is the headlight dim when you turn the key to the ON position ??

[jp9094]

Just an update. After having dinner, I returned to the bike and reinstalled the battery (I am on the road). It started right up!!!!!

The battery appears to be between 5 and 6 years old (I know, near the end of it’s useful life, but it is an OEM marked battery).  The lights and warning like came on with no problem, and appeared to be correct. I was so desperate I tried to get a new starter relay from the auto parts shop where I had it tested. Not in stock!

As a side question I have been having problems with the cables attached to the battery I use to trickle charge the battery and run m phone while riding. The 15 amp fuse in the positive side of the cable blows at the drop of a hat. Could it be from the proximity to the motor and the heat? Would love to know. Any and all ideas appreciate.

Thanks to all.

[mrclubike]

Sounds like someone has added a fuse in the Red 12gage wire that feeds the positive to the electrical system
If so 15 amps is not big enough it should be more like 30 in my opinion (nothing to do with ambient heat)
I have added a 40amp to mine plus others in the circuits BMW failed to protect from the factory
The stock fuses only protect  the lighting and horn circuit
That is why some one has added the extra fuse (very good idea)
 
You need to get a volt meter and try to understand how to use it

Other than that I can only tell you what may be the problem with your starting in the order that   is most common
By the symptoms you describe
 
First would be high resistance in the grounding cable or the 4gauge cable going to your starter
 
Second would be starter going bad

 Third  guess is a battery issue either it is bad, weak  or  not charging 
Sure 12.7 is good with no load but what does it do during cranking
(the reason you need a volt meter is to test it on the Bike)

Unless you have changed the location of the pins in the relay socket and added a diode in the circuit  you Will Not find the correct relay at any local auto parts store

[Matt Chapter]

If the battery is an AGM type, the failure mode may not be gradual as with a "normal" type.  The AGM types fail all at once.  As mentioned you could also test the battery with the starter load, although the auto parts testers may do a similar thing.

[Bob_Roller]

Just for a little info on the starter relay, this part is unique to BMW motorcycles .
There is a diode wired in, if the diode isn't there, the green neutral light will come on when you pull the clutch handle in .