You cannot keep a chain on the biggest front and biggest rear teeth at the same time. The chain will fall off the front and/or fail to make it to the biggest rear. In addition to learning the limit screws mentioned in the last post the o.p. needs to learn riding technique. Unfortunately I don't live in R.O. anymore. I would put my request in Craigslist in the activity partner section. You don't really need a mechanic, you just need someone who rides and is willing to 'splain some stuff to you.

H