I just found that there is a discrepancy with the C60 I got and the booklet that came with it. I bought it new, but the book shows the voltage range for Bulk stage from 15-17 volts, but on the circuit board of the C60 it says the range is from 13-15 volts.  
Also, the book says that the float range is 14.5 - 16.5 volts, but the circuit board on the C60 itself says the float range is 12.5 - 14.5 .

I had my Bulk set at 13.5V according to the circuit board itself, and the float at only 12.7v.
But I suspect my main problem is my dump load not being big enough wattage.

For a dump load I have been just using one 12v (200watt) car heater (one element) with a separate fan.  I like doing 'heating experiments'. (200W is about the max of my power generation right now)

  According to my meter, it is 2.4 ohm. Thats higher than I had thought.

Therefore I see what I need to do. Parallel another heating element to get it down to around one ohm.

I suspect the poster may want to do what Flux suggested and reduce the bulk setting down, maybe to 14v and see if that does the trick.  On a windy day, you probably have plenty of extra power going to the dump load anyway.