1981 kz750 Ltd is knocking and not reving pass 2k

Hello all! I'm 22 years old and trying to pick up a new hobby while finishing school. I recently purchased two bikes in one week. I haven't owned any bikes before now, but I have a basic knowledge. My first was a 76 kz750 which I got started and trying to sell right now. Did a paint job and simple clean up. The bike that I just started tonight for the first time is a different story. It was in pristine condition and no rust and good all around, only has 2k miles. The breaks didn't have pressure and it had not been started for 15 years. So I crossed my fingers tested compression (each cylinder had 150 psi)and bought it.

After getting it home I cleaned up the tank and carbs. Tonight I realized the petcock had a nipple removed and I tried using the 76 tank that doesn't have a vacuum petcock. The third carb overflowed with fuel which is suppose to connect to the vacuum side of the petcock. However, after I purchased it I did put a small amount of oil in each cylinder in hopes of freeing any rings that may be stuck. I fired her up tonight and she idled great, but it would not run off the choke, and due to the oil I added it smoked a lot. It also made a knocking noise which seemed to be coming from the right side of the engine. It seemed to knock more right after I would lay off the throttle and it returned to idle. Like I said before it would not go above 2000 rpm and after the knocking started I got scared and stopped the engine.

I am going to order a new petcock tomorrow. My question for you all is if this problem sounds familiar. I have read a lot about carbs being off sync, or bad fuel but my other bike ran fine with the fuel, or a leak in the exhaust. I want to know if I should be worried about anything in the lower engine. It seems weird that I would need to rebuild an engine that only has 2k miles, but I have no idea truly.

I would appreicate any advice and I do plan to sync the carbs this week when I get the tool from the shop at school. I am part of SAE Formula car at my school and get to get my hands on lots of good things!

Clean out the float bowls and jets. Here's a link to one of my threads. There's more here too.
Steve
kzrider.com/forum/11-projects/598262-kz-...-will-it-live#672882

Sure synching is a good idea, but checking for vac leaks (manifolds, air box boots) and cleaning the carbs are your first stop. 9/10 I don't have to end up doing a sync unless I really want to pull the last little bit out of the bike. Usually I just end up riding as is.

Also don't forget the simple things, spark on all 4, nothing loose, oil level okay. When you changed it before starting it what'd it look like? (You did change it right? Old Dino oil becomes acidic after 3-6 months, eating away at any soft bearing material it contacts...) also. Bit of a peeve, it's brakes, not breaks.

Verify oil pressure is ok. Knocking from the right side could just be the primary chain noise these engines all seem to have. Syncing the carbs makes it less noticeable (if they are out of sync). Raising the idle speed also seems to quiet it down.

I would remove the carbs, clean them, check for vacuum leaks (especially around the holders/boots), and then perform the synchronization. When I got my 82 750 ltd it sounded like a rock tumbler at idle. After cleaning the carbs, replacing the holders, synchronizing, and setting idle speed to 1100rpm, it's much quieter.