How do you implement a stream that properly handles backpressure in node.js?

I can't for the life of me figure out how to implement a stream that properly handles backpressure. I have a test script I'm running:

var stream = require('stream')
var util = require('util')

var highWaterMark = 10

var Streamer = function() {
    stream.Readable.call(this, {highWaterMark: highWaterMark})
    this.count=0
}
util.inherits(Streamer, stream.Readable)
Streamer.prototype._read = function() {
    this.startStreamin()
}
Streamer.prototype.startStreamin = function() {
    this.pausedYo = false
    setTimeout(function() {
        if(this.pausedYo) return
        // else

        this.count++
        if(this.count%10 === 0)
            var data = "_"
        else
            var data = "."

        if(this.count > 500) {
            this.stopStreamin()
            this.push(null)
            return
        }

        if(!this.push(data)) this.stopStreamin()
        process.stdout.write(data)

        this.startStreamin() // keep streamin
    }.bind(this),200)
}
Streamer.prototype.stopStreamin = function() {
    this.pausedYo = true
}

var StreamPeeker = function(myStream, callback) {
    stream.Readable.call(this, {highWaterMark: highWaterMark})
    this.stream = myStream
    this.reading = true
    this.callback = callback

    this.stream.on('readable', function() {
        //process.stdout.write('reading: '+this.reading)
        this.sourceReadable = true
        this._readStuff()
    }.bind(this))

    this.stream.on('end', function() {
        this.push(null)
    }.bind(this))

    this._read()
}
util.inherits(StreamPeeker, stream.Readable)
StreamPeeker.prototype._read = function() {
    //process.stdout.write('start')
    this.reading = true
    if(this.sourceReadable) {
        this._readStuff()
    }
}
StreamPeeker.prototype._readStuff = function() {
    if(this.reading) {
        var data = this.stream.read()
        if(data !== null) {
            if(!this.push(data)) {
                this.sourceReadable = false
                this._stopReading()
            }
            this.callback(data)
        }
    }
}
StreamPeeker.prototype._stopReading = function() {
    //process.stdout.write('stop')
    this.reading = false
}



var a = new Streamer()
var b = new StreamPeeker(a, function(){})

var looping = false
var loop=function() {
    var data = b.read(5)
    if(data === null) {
        looping = false
        return
    }
    // else
    process.stdout.write(data.toString().replace(/\./g, 'x').replace(/_/g,'L'))
    setTimeout(loop, 1000)
}

b.on('readable', function() {
    if(!looping) {
        looping = true
        loop()
    }
})

The output should ideally be something like:

.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL
.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL
.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL
.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL.....xxxxx...._xxxxL

But instead I'm seeing something like this:

....xxxxx...._........._........._........._........._........._........._......
..._........._........._xxxxL_........._........._........._........._........._ 
........._........._........._........._........._.....xxxxx...._xxxxLxxxxxxxxxL
xxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxL
xxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxLxxxxxxxxxL

A: Why are there 4 dots and then 5 x's in the beggining, but mainly B: What am I doing wrong with backpressure?