What did they do as part of their service? The backfire, or popping, could be from a few things: running too fat, running too lean, exhaust leak at the head. The first two are unlikely, but if they removed the exhaust, they may have mistakenly left the old exhaust gaskets in and then put another set in, or they may not have tightened the pipes to the head well enough.
You could also check to make sure the vacuum line to the ACV in the carb is not damaged/leaking.

 

So the 12000 service was
Oil filters plugs valve clearances head bearing check clutch check adjust brake inspection believable were more minor inspections done that I haven’t listed basically as listed as a 12,000 mile service by Honda

 

To add to Brett in post #2: Those are aftermarket pipes. They may not have been removed, but from when they were installed, the aftermarket pipe flanges are thinner, and in tightening them to 17 ft./ lbs, unless a couple flat washers were used under the nuts that tighten the flanges, you cannot achieve 17 and get a good seal, even after changing the exhaust gaskets. If the stock acorn nuts are present, they bottom out on the exhaust studs before achieving 17. The flat washers make up the thickness difference from the stock flanges. If you don't use flat washers and over-tighten trying for a good seal, you risk pulling the studs out of the head. Examine them thoroughly and understand.

 

Thank you guys you’ve been a great help.
I did try posting things on Facebook asking the same questions but it looks like Facebook’s only good for posting pictures.

Nice one, Johnny English

 

Friend, you have a straight-through exhaust system. Due to incorrect carburetor adjustment, pops in the muffler are possible. This is the fuel burning out. You need a carburetor adjustment specialist. I had this on my Yamaha Drag Star

 

Interestingly, he didn't have this problem before the service. But i agree if the exhaust pipe were not removed at the service, I would start looking at the carb.

 

What year 1300S?
Has the PAIR valve been plugged at the Reed valves??? You can plug it there with RTV or add a screw,,
Remove PAIR stuff.
Vacuum hoses crack/split at the hose ends.

Honda VTX 1300 Desmog | Bareass Choppers Motorcycle Tech Pages

This is a walk-through for removing the PAIR valve assembly, and all the hoses and junk that are associated with it, on the VTX 1300 49 state model. I have never dealt with a CA model (living in Louisiana) so if anyone wants to take good quality pics, write a description and email it all

tech.bareasschoppers.com

https://www.vtxoa.com/attachments/1300-pair-reed-valve-block-jpg.214390/

 

I recently had an issue with my bike after doing maintenance and had popping on the decel as well. After a while I decided to check my valves for clearance. In doing so I took the air filter box off and found that it had been put on wrong with a very small gap as the screws did not line up correctly. After I made that adjustment, I no longer had the popping on decel or when I released the throttle. It could be simply something that small. Pull the air box and make sure that it is seated correctly.

 

Is it the OEM air box and the tab that latches into a piece on the backbone??

 

I’ll have a look, thanks