PROBLEM 1

I got it going. Come to find out it had a bad timing chain. So I get it replaced. A couple of weeks go by, I need another new timing chain. I get it fixed, Again... Why? What can be causing the chain to "stretch"?

PROBLEM 2

A couple of months back, I buy a new carb. I was supposed to have bought a 570 cfm, but ended up getting a 770 cfm, to my suprise. I think that this is too much carb for my 318. Keep in mind that it is all stock, except for the carb. It's causing my plugs to foul in a very short period of time. Should I get a smaller carb or do something to the engine?

I could really use some information.