Back Fire and popping at low Rpm

Hello every one.
i am hoping to find a solution to my problem. what i have is. A 1982 kz1000J bike has 6700 miles on it an has been sitting for a long time when i got it but ran when parked. My problem is at 4000 rpm or less it back fires (extremely load) and pops and caries on. 4000 rpm and higher it runs perfect rev's right up no pop no back fire will hold any rpm you wish above 4000. Things that have been done to fix this. New- plugs,plug wire, new pod filter, new mixture screws and o-rings, carbs have been cleaned multiple times,There spotless, i only changed the main jet up one size, carbs have been set and check multiple times, carb boots are not leaking they have been checked, and valves are in spec. if any one has any idea that would be great im running out

Cam timing out a tooth?

i dont think it is the cam timing because it was never messed with and it did run good at one point it started doing this when the carbs were hooked up being synced How would i check if its the timing advancer and could this be my problem ? the bike was close to being done ran pretty decent to the point were i rode it for a couple short distance rides figured sync the carbs and i was done

Timing light...

could the advancer be my problem or should i be looking elsewhere

Your model = no moving parts, all electrical so most likely not...
With timing light, you can confirm if your pick ups @ "F" & advanced marking are working to spec but.... since operating at higher rpm most likely not your problem.

You have BS34 carbs...?

Were pod air filters always on this bike or did you just add them recently...?
BS 34's & pods, others have had issues dialing them in, stick with stock air box...

You mentioned jet size change, reasoning (new cams, 4-1 exhaust, head P&P etc...)?
Put the old jets back in and see if problem still there...

If all electrical/ignition timing/valve clearances etc... good, I'm thinking your carbies/jetting are the issue.

those are the carb i have. there were pod filters on this bike when i got it (air box wasn't there) i replaced with new k@n pods i went up on main jet only because of pod filter kept being told i had to because of the pods i am confident its not the electrical as it was gone over a lot this a multi-meter
i will be putting stock jets back in today

So the problem was solved by putting the plugs back that cover the pilot jet and starting over again with the set and sync, And i did leave the bigger main jet in. Bike i ready for riding

Steve1986 wrote: i dont think it is the cam timing because it was never messed with and it did run good at one point it started doing this when the carbs were hooked up being synced How would i check if its the timing advancer and could this be my problem ? the bike was close to being done ran pretty decent to the point were i rode it for a couple short distance rides figured sync the carbs and i was done

Popping means lean. The old rubber intakes are notorious for leaking air. might want to check them.

i thought popping meant lean as well but all i did was add the plugs back in i mentioned and during setting of carbs i set for more air with mixture screw and it stopped popping runs and starts like it should know but during my problem hunting i did check the rubber intakes they were fine.

Does it still have the vacuum switch valve (the thing that sits above the cam cover) I've heard removal or incorrect operation can cause a backfire condition

Steve1986 wrote: could the advancer be my problem or should i be looking elsewhere

I just oiled mine, I took the non adjustable plate off there and went to town with my 3 in 1 oil.