voltage regulator

Hi everyone. I'm new here and have a problem with my 77 type 2. I upgraded to a 70 amp alternator but I am still using the 55 amp regulator that was origanally on the vehicle. I am having issues with charging. The volt meter I installed occasionally jumps around a bit, and, when I first start the vehicle it stays at 12 volts until I "shock" it by briefly activating the solonoid switch I use to charge the second battery then it appears to charge correctly. Any thoughts or tips would be much apreciated. I had a lead on a 70 amp regulator but after I placed my order the company said it was not available and they could not track one down.
Cheers Surprised