Hello, I recently did a engine rebuild from 72cc to 110cc. I changed the crank, cylinder and the cylinder head. It starts up fine and idles decently. When I give it throttle the rpms from 2k to 4k go up smoothly, but after 4k it seems like it doesnt want to rev up. When riding it, it bogs really hard, but then all of a sudden the rpms rise fast and if u change the gears fast and take off the throttle fast it rides good, but if you let off the throttle just a little for too long it starts bogging again, what could cause this? I tried looking for air leaks, found none, carb cleaned, changed spark plug, the fuel flows good from the tank to the carb, also tried another carb.

 

Still most likely to be the carb jetting, but getting the same problem with two different carbs points to something else. Check the earth to the frame and engine, and engine mounts for tightness.

I once had a Honda 300 that did this and it turned out to be the CDI, very rare that CDIs work but not properly, however this one did. Worth trying a new coil and CDI as they are quite cheap for those little machines.

 

I tried so many diffrent parts that forgot to mention that I tried 3 different CDIs and 1 diffrent coil. I will have to check earth for the frame. Thanks for your advice