KZ440 engine knock and won’t rev past 4k

Not my bike but a friends. He put 87 octane in the tank and then rode on the high way and it developed a knock and wont rev past 4K. The bike burned a little oil before the knock. We replaced the spark plugs and the old ones were oil fouled but otherwise normal. The exhaust on the left side leaks an oil and gas mixture. My guess is the ignition timing is out of sync. I’d appreciate any suggestions on what could be wrong/ what to check. -Thanks

Based on the description, I will be surprised if ignition timing is the culprit.

Has the bike been properly maintained? Is the engine oil level correct? Is it the correct oil for the engine?
A leaking valve seal may have caused so much carbon buildup on that exhaust valve, that it can no longer close. Worse, the head of the valve could be broken off.
Where is the oil leaking from the exhaust? At the head? If so, that can contribute to the knocking sound, and is easy to fix. At least the exhaust leak is. The oil coming through is a different matter.
Have the valves been adjusted in the last few decades?
Are the carburetors properly adjusted?
Any modifications, like no air filter, chopped of exhaust system, et cetera?
Yes, there are many possibilities. More information will help board members make useful recommendations.

Thanks. It has stock air box and stock exhaust. Oil has been monitored and changed regularly. Valve clearance has been checked. New spark plugs. It did burn oil before.

I attached a video of the tapping. Looking at it from the rear the left side appears to have more smokey exhaust, so I'm assuming that's the side with an oil leak. I will double check valve clearances.

Are both cylinders firing? An easy test is to spray a little water on each exhaust pipe near the head. while the engine is running. The water should immediately sizzle and quickly evaporate. If one side is much slower, that cylinder is probably not firing.

Next on my list would be a compression test, or even better, a leak down test.

That is a rod knocking.


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Now that you mention it. Yeah that sounds like a rod knocking. rip

Yep thats a rod. There is no fixing that without a complete teardown.