Need carb help

[whiteman350x]

Ok here goes. 4-stroke carb tuning. Starting with completely rebuilt motor. It has been run aprox 2 hrs to break in. It will crank fine, it will run at idle, it will not take the fuel if you get on the throttle fast, it will take fuel if you throttle up slowly, but it pops fire out of the exhaust. It will not run well enough to do a high speed plug check. This is what I have done, drained, cleaned and dried tank, it has fresh gas. Dropped main jet sizes and it helped some. It is at stock main now. The needle is some type of aftermarket so it only has one clip grove. The bike suposedly ran fine before the rod broke. But it will not run right after the rebuild. What do I need to adjust and which way lean or rich? I know this is very general, just looking for basic carb theory.

Thanks

[Autophysn]

I am sure you have read thru carb jetting 101 by Dammitt right?

Sounds to me like a big problem is that needle only having one clip setting. As for it popping and fire coming out the rear, well that sounds like an accumulation of fuel in the combustion chamber, then a late spark.
Have you checked the electronics, strength of spark, plug gap, valve adjustment, timing? I would start by looking over the basic mechanics of the engine before moving forward. especially since the motor is fresh, the valves could have fallen out of adjustment or ?
Take a deep breath and go back over everything, you will find it, just be patient.

you never said what kind of bike it is? just 4 stroke

sorry, wish I could help more