C# read byte pattern on large file

I'm new in C#, I want to count up a byte pattern inside of file. Everything is ok when I try to read a small file (8MB) and got 1907 in result, but when I try to read a large one (50MB) the app is freezing and return nothing. This is my code so far ..

public long chunkMethodCW() 
    {
        int incomingOffset = 0;
        byte[] outboundBuffer = new byte[1024];
        long CW = 0;
        KMP kmp = new KMP(header); // header = pattern in hex

        while(incomingOffset < data.Length)
        {
            int length = Math.Min(outboundBuffer.Length,data.Length - incomingOffset);

            Buffer.BlockCopy(data,incomingOffset,outboundBuffer,0,length);
            incomingOffset += length;

            //CW += kmp.match(outboundBuffer);
            CW++;
        }

        return CW;
    }

    // KMP Class 
    public class KMP
    {
        private int[] F;
        private byte[] pat;
        private int m;

        public KMP(byte[] pattern)
        {
            pat = pattern;
            m = pattern.Length;
            F = new int[m + 1];

            for (int i = 2, j; i <= m; i++)
            {
                j = F[i - 1];

                if (pattern[j] == pattern[i - 1])
                {
                    F[i] = j + i;
                    continue;
                }

                while(j > 0 && pat[j] != pat[i-1])
                {
                    j = F[j];
                }

                F[i] = pat[j] != pat[i - 1] ? 0 : j + 1; 
            }
        }

        public int match(byte[] data)
        {
            int n = data.Length, pi = 0, ti = 0;
            int matches = 0;

            while (ti < n)
            {
                if (pi == m)
                {
                    matches++;
                    pi = 0;
                    pi = F[pi];
                }

                if (data[ti] == pat[pi])
                {
                    pi++;
                    ti++;
                }

                else if (pi > 0)
                {
                    pi = F[pi];
                }
                else
                {
                    ti++;
                }
            }

            if (pi == m)
            {
                matches++;
                pi = 0;
                pi = F[pi];
            }

            return matches;
        }
    }