Deceleration popping is something regularly encountered with replacement exhausts on Harleys. It is the exhaust causing the bike to run LEAN, not rich. Just like an air leak is leaning the exhaust mix. The exhaust has enough air to ignite unburnt fuel in the pipes.
I hear Hondaman regarding slow mix screw in for lean, out for rich. Respect to you for your knowledge here, but my experience has been out = lean on the pre-PD / roundtop carbs. Just like an air screw. Do what I did, experiment with small adjustments both ways and see what works.
M, so would you suggest going more in and therefore more rich to see if that has any effect on the popping?
Hi, yes, i would. At deceleration, you are on no throttle. So, you are correct that the combustion is from the carb's idle circuit, assuming no significant leaks. My experience with deceleration popping on Harleys was curing them by richening the mixture. I was sceptical, as it seemed counter-intuitive to allow more fuel in. The advice I was given by multiple sources was clear, though. When I followed it, it worked.
As to whether screwing in or out is the right way, I found a fraction out reduced sooty plugs on 2 of mine, having previously tried a fraction in, which only made them sootier. So, my experience with my roundtop 750K6 carbs, the screw works llike an air screw, where out=leaner. But, advice on here, particularly from Hondaman (who no argument, is clearly very experienced, helpful and expert), suggests the screw is not an air screw, but works more like a fuel screw (I.e. the opposite way, or out=richer). The UK SOHC forum takes the view the same as my experience, the screw works like an air screw and out=lean, in=rich. Confusing, so I would suggest you try 1/8th in from current and see how you go, knowing I may be wrong and if not improved then try 1/8th out from current. Luckily, it very easy to experiment 👍.
