I was wondering if you made any changes to the slide(drilled hole,or tied down spring coils)?
for quicker response
Any chance of air leaking at where you desmogged?
Does California model have different ecu?
marc

 

I have a powercore4 and the same jet kit as the op and at stage two on a stock bore bike I have no popping on decel. Why I have no idea just the way it was after the mods, I had one before the jet kit.

 

I followed the DynoJet instructions for that kit (2152) so all I did was swap the stock spring for their spring. No slide drilling or coils tied down. I also wonder if the slide or main jetting would have any effect. I'm still trying to understand if the slide would be up, partially up, or down when in a high RPM coasting situation with the butterfly valve closed. If it was up I'd assume there'd be a lot of gas entering and bikes wouldnt need the ACV. But they put it there (on other carbs) for a reason...

As far as the desmog, I have a BillBlue block off plate on the air induction port. I did get a new gasket which I havent put there yet just in case, but the bike was new when I put the plate on so I'm not sure I'd need it. I'll swap it this weekend anyway.

Does the powercore4 offer more backpressure than a stock KLX300 exhaust? Maybe that's the issue.