KZ900 Bore Question

I just bought this 1976 KZ900 but the PO said the engine had been bored out but wasn't sure to what size. Is there anyway of telling? Also the heads say "APE" on them? What are these? I have included a pic.

Head close-up

APE. means American performance engineering.They are a very big parts comp. They sell those half moon cam plugs.The only way to know the piston size is to measure the bore diameter.

could be anywhere from 903 to 1197;)

Could be bored or just honed as some folks call a honed engine "bored"! :blink:

Unless you're going to open it up I wouldn't worry about it. If there is plenty of compression and you get a good result from a leak down test, I'd leave it alone. You can check for proper carb setup on the "bored out" job by doing a colortune. From the looks of the outside of the carbs I'd say that is where you need to spend some time for sure. Clean them, re-balance and see what it does. If it bogs or pops then address the carbs jets/needles.

The bike is a find at 4 times that price, good fortune has smiled upon you!