Speedmaster 865 Battery Draining On Start

Are you saying the same thing happens with a new battery?

 

Check your earth terminals for corrosion. Did you keep it inside?

 

If you have a multimeter and BEFORE you disturb anything, run a continuity and resistance check first.
Pick your contact points carefully and ideally run from the base of the battery post, not wire connection, to the starter motor mounting bolt.
Let us know your findings?

Obviously the above is for the negative but a similar test could be performed on the positive side.

 

Set the multimeter to the 12v DC range, then connect the positive lead to the positive battery post and the negative lead to the positive terminal on the starter motor. This will give you any voltage drop under load through the cable itself and the starter solenoid while cranking the engine. There should be virtually 0 drop. If thats good and the battery is new it must be the starter itself.

 

So based on that and your next post, the wiring and battery connections check out as good and no further work needed on those.

Just in case its anything to do with the solenoid, I have known it before on other bikes, do a voltage check coming out of the starter solenoid with the starter switched pressed ( you will need to disconnect lead from the starter motor end and insulate it).

Do you get full battery voltage?

If yes then starter motor is your issue.
Pull the starter motor and give it a once over as that is sounding like the culprit.

 

The 13.8 v means the battery is fully charged and the connection to the starter is open circuit (solenoid not engaged). The 2.5v reading when cranking is way too much. It means you're losing 2.5v between the battery and the starter motor which is basically 2.5v less to run the starter. It should be as close to 0v as possible with 0.5v absolute max.
Either the solenoid itself or cable connections could cause this drop. A bad connection can still show 0 ohms resistance with a meter but it will increase when under load and required to flow 100A or whatever the starter draws. You could try briefly connecting a jump lead between the + battery terminal and the + starter terminal to see if it cranks, doing so with the multimeter connected across the battery (12v range) will show drop at the battery which should be less than 2v. The starter could still be a problem but that 2.5v drop across the cable and solenoid needs sorting.

 

The problem is, testing as above and not on full load, onerous readings can arise i.e. resistances can appear to not exist.

Under the circumstances you described I'd go for corrosion of the starter motor bearings or electrical contacts. A simple strip, clean and grease may solve your issues.

 

Had this issue with my 900 America and it turned out to be the CCA was not enough. you need to have at least 210 CCA to turn these puppys over well, mostly because of the head light drawing power with ignition turned on.
i didn't read all the posts in the thread here but I went to a higher CCA and problem solved. hope this helps.

 

That battery is far too weak for these bikes. Be careful or you may damage the sprag clutch.

 

I searched on Amazon this is the Battery I purchased and works great its 210CCA hope this helps.