New guy here searching for some answers and struggling with Google searches...

I have a '90 Trailblazer 250 that I dug out of storage last year and sent to my buddies shop to have gone through and make run again. Apparently he had a kid who was real sharp on ATVs and dirtbikes so I figured I'd give him the business to help out his new business and save me time I didn't have. Long story short, the kid wasn't all that he was cracked up to be and I'm still trying to get it sorted out.

The top end was rebuilt with Wiseco stuff twice while at the shop. Apparently the oil pump wasn't working and they lost the first one. It was then decided to just cut the lines and plug them and run pre-mix @ 40:1. The carb was totally gummed from sitting for years and was replaced witha Polaris carb and what I can only assume are the stock sized jets in it.

Since I've had it back I've put a new coil and cdi box on it, and a new plug gapped at .028 (one from shop was .052). Though it runs and idles fine once warm (cold starts need ether after sitting a few days), it has no low end power. I can barely take off from a dead stop without a 3/4 throttle input, and then it crawls at first. At half throttle and cruising it will decide that it wants to go and speed up more without any throttle input. Then at the top end it will pull hard for a minute then fall on it's face and start surging. Then an occasional backfire from the carb.

I have read that when doing the oil-pump bypass that I need to re-jet the carb due to the thicker nature of the fuel. If I am running a #145 main and a #40 pilot jet stock, what would be the recommended sizes to step up to? This is a completely stock set-up with no air-box or exhaust modifications. And while I am at it, does the oil line from the pump to the engine need to be disconnected as well? It was left on and the inlet line from the reservoir was cut and plugged.