/diy/ - Do It Yourself

Vintage motorbike capacitor guy from last thread here.
I grabbed a few 1000uF capacitors from my old as fuck capacitor jar.
Tested them with my power supply to replicate the bikes voltage and measured the output and voltage was nominal and when I cut the power I got one or two seconds till discharge.
So I replaced the battery in my bike with this and it ran poorly, under low revs,stalled, and my lights blew.
So I tried again with 400uF and same result.

Output voltage was exactly the same as battery, and in check with what the service manual specified.
Wheres my mess-up?