I was battling this EXACT issue, but I have a BIG 155+cc motor, so I knew it would be a problem.
The way I solved it was by hooking up batteries in parallel. I have a 230CCA battery in my Coleman starter, and a 670CCA battery connected in parallel to that.
Now, WHY you are having that current capacity issue is a different question. My KPV started no problem with just 230CCA, FYI.
What kind of motor are you trying to start?