1982 kz750 spectre

My new kz750 is having trouble Idiling and is back firing. It only idles on at least half choke. At half choke it jumps between 1000 to 1500rpm. Also the farthest left cylinder is back firing. I'm going to do a compression test and recheck the spark on all the cylinders but don't know what to do next. I think it is most likely carb problems put I never heard of carbs causing backfires.

Might want to check valve clearances. I don't know for sure about your bike, but mine wasn't hard. Your's should be similar. We had a similar problem with my brothers bike (90 Honda cbr600) it wouldn't hardly idle or rev up. He rebuilt his carbs, bought new coils and spark plugs, I think he bought a new ignition computer (igniter? I forget) as well, and after lots of trouble shooting later. Ended up his exhaust valves were too tight. It's a maintenance item that is easy to neglect so it is worth checking if you haven't already.

Cleaning your carbs is the right of passage with owning most 34 year old motorcycles. The factory service manual will help and is strongly advised. Don't waste money on "carb kits," rather, get new O-rings and take the carbs 100% apart to clean. Pulling the float bowls and spritzing carb cleaner on the parts won't get it.

I have a Haynes manual so I will clean the carbs and check the valves when I can.