ATC 70 runs lean. Need advice

[Mike O]

Just finished restoring my 85 ATC 70 and having trouble with what I think is a lean condition. Engine is rebuilt, CDI conversion, brand new Honda factory carb, totally bone stock including air filter. only mod other than CDI is a Spangler exhaust. engine runs fine at low speed and wide open but stumbles pretty bad at 1/2-3/4 throttle. Main jet is stock 58 and needle is in fourth groove. Plug looks ok and not black or rich. I dropped the clip to the last groove and set pilot 2 full turns out and it still runs bad in the middle. Thought about about upping the main jet to 60 or 62 to see what happens? Just don't understand why the stock carb setting would not work correctly on a stock engine? Everything is new, no air leaks or any issues with anything else. Any ideas or suggestions would be greatly appreciated.

[big specht]

Well the ignition and exhaust will change the jetting. Try going up acouple sizes on the pilot and putting the clip on the needle about the 3rd groove from the bottom and see how it runs. I have a stock 70 with stock exhaust and air cleaner and points BUT I’m running 100ll av gas in it and it need a bigger pilot jet cause the type of fuel I’m running. The pilot jet gets used for more than just at idle.