I don't think the new gx carb will work on the older engines. It takes about 4 gallons before it is really seated in. If you have the coated wrist pin in it the rod has already been replaced most likely. I honestly think I would just seal it up and run it. Just make sure you have the c-clip for the wrist pin seated in the slot all the way. I have seen and done one myself,get all together c-clip not in all the way even though it looked like it, it comes out so long psr! and god knows what else. On the carb. I like the carbs that have the red go logo on the front of them. for some reason they are the easiest to tune for me. One last thing.When yor engine is running great then seams to flame out or not running right. Do not assume it's the engine thats giving you the problem. I have only had 2 engine related problems. 1 was an air leak[that's why I said seal it up] the other c-clip popped off. other then that it's been broken clutch springs small crack in fuel line things of that nature. These engines setup and run in right will last a long time.