1982(83?) KZ550 C

Hey all, been a minute. Started on this back in early 2021, then life happened. Now that the weather is getting nice, figured I'd take her out of storage and try to get a properly functioning bike out of her. 

To sum up: Bike was given to me by an acquaintance when I mentioned I was interested in learning to ride. Unbeknownst to me, she was in pieces. So not only did I get to learn to ride, I got to learn how to work on it. I "rebuilt" the electrical system from the ground up (I learned a ton along the way, and plan to redo everything eventually, I just wanted to get it running) replaced the brakes, chain, carb boots, brake lines, master cylinder, brake lever, and clutch lever. 

The previous owner and installed a Dyna ignition system, and had the carbs rebuilt when he got rid of the factory airbox. 

The issues I had when I put everything together were pretty apparent as I got further into it. Right off of the bat, I noticed I had to give a lot of throttle to keep the bike from stalling as I let out on the clutch in first gear. Once it was moving, it was fine. Then, I noticed that the exhaust pipes for cylinders 3&4 were barely heating up, and never got around to properly diagnosing it before life happened. 

Fast forward to today. Changed the oil, changed the spark plugs. Previous owner had Champion RA8HC plugs, swapped them for NGK D8ea (2120) Did a compression test using a mittyvac compression tester, and everything had decent compression, but it was all over the place. I'll put those at the end, along with the running temps measured by a laser temp gun.

Also noticed that the bike will only continue running with the petcock set to PRI, so I'm guessing I'll have to rebuild/replace that. 

Was hoping someone would give me some next steps. I'm assuming I need to check the valve clearances, and I'll probably pull the carbs and get them professionally cleaned and synced. 

Compression checked after letting bike cool slightly after running for 10 minutes, with throttle wide open and all plugs removed. 

Cyl 1 - 150psi
Cyl 2 - 170psi
Cyl 3 - 130 psi
Cyl 4 - 125 psi

Running temps taken after running for 10 minutes. 

Cyl 1 - 150F
Cyl 2 - 150F
Cyl 3 - 93F
Cyl 4 - 78F

Yup, 3 & 4 aren't firing.

And yup again, the carbs need attention.  Most rebuilders are hacks, though, so consider doing the job yourself.  You are going to have to rejet quite extensively also, since the airbox is gone.  That won't cause the issue as mentioned, though.

I had made the decision to pull the carbs literally as I clicked to see your response, so I'm glad to see that was a good idea. 

What would cause those two cylinders to not fire? It's strange, because they're fed from different coils, and I checked before I replaced the plugs that they were getting spark. 

Plugged up pilot jets, and the pilot circuit though the carb body.  

Would it be worth trying to clean the pilot jets before doing a full rebuild, just to see if that is what's causing the issue? I ask because it looks like a full rebuild will run me close to $200 for parts.

I don't think it's a coincidence that the cooler pipes are also the cylinders with low compression (the difference between the best and worse is significant - normally 10% is a good guide so with a best of 170 your lowest should be around 153) I would suggest checking your valve lash before getting too deeply involved

I had the same thought. Little nervous as I haven't done much engine work in my life, but I gotta learn sometime. 

dthemac wrote:

I had the same thought. Little nervous as I haven't done much engine work in my life, but I gotta learn sometime. 

It's pretty straightforward to at least take your initial measurements, read the workshop manual over a few times and have it to hand when you do the work, remember it's not about how fast you can do it but that you take your time and do it right 

Okay so I popped the valve cover, and immediately noticed that I'll have to replace the gasket. It came apart in pieces. But I took the measurements, with some difficulties because I was having some trouble understand the FSM procedure. It said to take the measurements of 1&3 or 2&4 but that didn't make much sense if they're not both at 90deg to the housing. So I made my way through it and took measurements with the lobes at 90deg to the housing.

Valve Clearances
Inlet
5 - .1
6 -.06
7 -.1 tight
8 -.06 loose

Outlet
1 - .1 to .13
2 - .16
3 - .1
4 - less than .04

Assuming your measurements are correct you have some work to do. The amber ones below are at "minimum" tolerance and the red are too tight. They should all be at the upper end of the factory spec

 

How do I know I did it correctly? Following the steps in the FSM was pretty easy up until it tells to measure 1&3 or 2&4 at TDC. 

dthemac wrote:

How do I know I did it correctly? Following the steps in the FSM was pretty easy up until it tells to measure 1&3 or 2&4 at TDC. 

Check out the below post from Zed1015

Valve Lash 2005 KZ1000P - KZRider Forum - KZRider, KZ, Z1 & Z Motorcycle Enthusiast's Forum