You need to configure the http4 endpoint to allow more concurrent connections to the same remote host.
Start with
And then checkout the Apache HTTP Client 4.x documentation / api to know which option to set to increase this.
Or switch to use jetty-http instead so you just use Jetty for both consumer/producer as that works as well, and I don't recall Jetty have such limitation out of the box. See more at: http://camel.apache.org/how-to-use-camel-as-a-http-proxy-between-a-client-and-server.html