Kz250 bogging

Hi guys new to the group and new to motorcycles. And I apologize if this question has been answered although I did my best to search for it. I just picked up a 1980 KZ250 D1 from the original owner with 13000 miles. The bike ran ok with the exception of the dirty air filter. I replaced the filter with a pod type from the dealer. After replacement I noticed it to bog at low rpm the eventually cleared up. I removed the carburetor and cleaned to the best of my knowledge. After this it would not accelerate under load after 3000 rpm. Sent the carb to the dealership and they couldn't find anything wrong. I reinstalled the factory box and what was left of the air filter and still no change. It seems to be running rich based off the black smoke when it's bogging. I'm lost with this thing and out of ideas. Any help would be much appreciated. It has a cv32 carburetor. It idles and starts perfect just will not accept anything over half throttle under load.

Hi
Perhaps you need to check the timing. Retarded timing will cause this type of symptom. There's a "bob weight" advancer that advances the spark as the engine revs increase, it's behind the points back plate and should be free to move. The best way to check it's working is with a strobe gun, maybe you should get a manual this will explain it. Might be the timing is spot on, but at least you will have ruled that one out.

Good luck

Several problems can cause those symptoms. With a used bike, there is no way to know what, if any, maintenance has been done. Reinstalling the air box with a new filter is a good way to start. Without them in place, the carburetor will not function as expected.
-Check valve lash. It is too often overlooked and can cause the symptoms you list.
-Check the timing advancer to be sure it operates freely. If in doubt, pull it apart, clean and lubricat.
-Check ignition points. If in doubt, replace and carefully adjust.
-Inspect intake manifold and carb to air box boot. If hard or cracked, they are likely leaking and need to be replaced.
-Check fuel level in the carb using the clear tube method described in the factory service manual. (You will need the manual - get one)
-Check the ignition coil and secondary wire forcracks or anything else suspicious looking. Replace as needed.

There is more, but this will eliminate many of the more common problems.

Thanks for all the great advice guys. I took the bike to the shop and finally had it looked at. It looks like the previous owner had drilled one of the jets and it was just dumping fuel into the engine. Its funny how it ran just fine with a dirty carburetor but I guess it makes sense. Anyways the bike is up and running great. Can't wait to put some miles on it!