Well.

Now I'm confused.

@Yanmar Ronin I'm confused.

 

Now I'm confused.

Me too... 😅

 

lol

 

Find out the stock jet size and order 2 or 3. Then get some micro drills and drill one out by 3 or 4 thousandths. Replace the stock with that and see how it runs. Go another 2 or 3 thousandths at time until it seems a bit rich. (Maybe keep the choke closed one notch) that way when fully opened it will run best.
You have the stock original if you need it and 2 or 3 spares to screw up on.
Easy job tho. I have the 212 and did that. Went about 6 thou bigger and no more lean surge without a load and runs great when blowing.

 

I have not read every post here (3 pages). so maybe I am talking out of school but you can open the fixed idle jet with micro drills if that is what seems to be what is on your mind. I have tried that my self and ended up going back to the Preditor OEM jet. Keep in mind the idle jet is always working. If it is running just right under load and you open the idle jet it may very likely be too rich under load. They work together. What MJK1210 suggested on the main jet you can also try on the idle. My efforrts were on the 212cc. Maybe you can optimize your 420cc if you feel the urge. I do not know of an adjustable idle jet mod for a Predator. Maybe someone does.???? I would be inclined to take the advide on page one from Orangputeh. If it starts fine and works good under load and at high speed RPM (not too rich and not lean) leave it alone.

What RPM do you have the high speed set to?

 

I do not know of an adjustable idle jet mod for a Predator. Maybe someone does.????

Two different adjustable needle jets have been mention on this thread. They are out there.

 

I just wanted to throw this out there. Sometimes a popping exhaust is a leaking exhaust. If the pipe is sucking outside air into itself at a seam or a gasket it can backfire/pop.