that should be enough to crank it,that's what my partner has on his 150 intruder,if it is old it may be losing cranking power.do you have a volt gauge to see the drop when you crank it?I f the starter is is pulling too much amperage it will cause a slow cranking speed.Full charge it and have it load tested, if it is good check cable condition and connections.If you have to change it,get the most amps you can.