The V-stack is an engine part, you will need to call if you want to order engine parts. The V-stack will not help the condition you describe, first thing I would do is get some regular gas, 87 octane and don't worry about the 10% alcohol, will run for years without a problem.

Start over over with the carb adjustments, go here; http://www.rcuniverse.com/forum/m_90...tm.htm#9103251 see post #124 by Aussiesteve and follow those adjusting instructions.