Knocking sound at low idle

Hey everyone, first post here.

I recently bought a 1982 KZ750N Spectre. It's my first bike and I've only had it a week, so I'm pretty new to the game.

The bike is in great cosmetic shape and seems to be pretty mechanically sound to me except for one thing. When I first start it up, there is a strange tapping sound coming from the engine. I changed the oil the day after I got it, and being as how I live in steaming hot Florida, I filled it with 20W-50. The tapping sound usually goes away after I ride for about 5 minutes or so and get the engine warmed up. This makes me think that maybe it's normal, since it doesn't happen all the time. Idle is about 1025 or so, within the 1050 plus/minus 50 prescribed in the repair manual.

Any ideas?

My guess would be the valve clearances. Maybe a little loose and as it warms and the metal expands it quiets down ?

What's the mileage on the engine?

Is the noise coming from the gearbox rather than the engine ? Put a big long screwdriver to various parts of the motor and put the handle to your ear - crude mechanics stethescope but it works.

The primary chain in the gearbox connects the crankshaft to gear shafts or clutch and rattles quite a bit. Mine used to sound like a bag of hammers and synching the carbs helps lessen the rattle. Hopefully something simple like this

If the bike is running strong, I would take a long ride and change the oil (15-40 Rotella) and listen again. A little clatter is kinda normal, right? If it's valve noise the thing would be a dog.

Carb sync helped me big time when i got my kz but i knew the valves were good

Hmmm not quite sure where the sound is coming from exactly, I didn't get down there to see but I'll try the screwdriver trick...I'm going to go out and mess around with it tommorrow, been wanting to bleed the brakes and Seafoam it (unrelated, I know).

Engine has 9000 miles on it.

That's primary chain noise. A carb sync will help.

It should go away as the bike warms up.

Thanks for the advice guys. It sounds like it's coming from the very bottom of the engine, maybe the transmission. After talking with a couple of small engine mechanics where I work, I think that the assumption that it's the primary chain is correct. One of the guys also mentioned that when I turn on the bike with the choke, the bike should idle higher than normal, because of all the extra fuel being dumped in the carbs. He says he would imagine it should idle at around 2000 whereas book says normal is 1050. However, idle with choke is usually around 750, and if I walk away without holding the throttle open for the 1st minute, it has a tendency to drop and drop and putter and die. If I hold it around 1500 until it warms up, it seems to have no problem with it. Any ideas on this?

Also, I have a post up in the electrical forum, I had some unrelated problems yesterday if anyone would like to take a look: www.kzrider.com/forum/4-electrical/59031...fuse-amperage#599219

Again, thanks to everyone on here. I used to own a 49cc scooter and was always asking questions on the ScootDawg forums, it's the awesome people like you that help me troubleshoot and save myself an assload of money at a repair shop.

After the bike is completely warmed up what rpm does it idle at with the choke off Ed

650ed wrote: After the bike is completely warmed up what rpm does it idle at with the choke off Ed

Idles at just over 1000 when warmed up