If IRC, your 48 is a magneto equipped Cub right? If so then what you have is indeed connection problems. Also, not being able to boost/jump start through the battery tells me that, and being able to pull start it pretty much confirms it. Generally this indicates bad grounds. Especially as Larry indicated :
Buzzard Wing wrote:I prefer a braided one to the bottom of the battery box, that is directly to a casting.
This is what I use and it has been a real dependable ground. Make sure that the starter lug is clean and no corrosion present.
One thing to check as well is the condition of the battery. I had this exact situation when I went to start Ellie after she sat since the beginning of October last as I was too ill to do much over the winter. Couldn't boost, the trickle charger would not charge - went into fault mode, the charger wouldn't charge the batter. Took it in to the shop, did a load test - toast. New battery and poof .. problem solved
There is always that fix too .....