Hi all

Hi everyone, Benno here, 20 year old Z650 owner hailing from the Great Southern Land. I'm a first time roadbike owner (had dirt bikes before) and I decided to pick up a Z650, or a KZ650 as our friends in the states know 'em as. It's an '81 that's been done up by the previous owner before me. Clip on bars, pod filters (urg), a 4 into 1 exhaust, engine rebuild, frame and cases sandblasted and painted (the alloy cases were polished), SS allen key bolts for all engine covers etc., just about everything new. She's a beaut.

One catch (isn't there always a catch, haha). The rings have gone in 2 and 3, or at least he thought so, from running lean.

As soon as I got it I cleaned the carbs out, and I got it running on 2 cylinders (3 and 4). I took it for a burl up the street and the headers on 1 and 2 were hot after a quick blast at wide open throttle, so I suspected the idler jets were blocked still in carbs 1 and 2. I re-cleaned them as well as I could (the idler jets in 1 and 2 are stuck in there, I'll have to use and EZout tool to get them out...my fault) and put it back together, and I cleaned the tank and put new fuel lines and fuel filter on it, filled the tank with fresh fuel, and it's still only running on 3 and 4, maybe sometimes on 2. I have to use starting fluid to get it going.

I tested the compression and in 2,3, and 4 it was 150psi each, and 1 was at 140. I suspect there's so much oil in there the compression reads higher than it effectively is. My goal now is to check the valve clearances, and if they are in spec, I'll be pulling the head and barrel off for new rings. I'll have to put them on myself, as I was quoted 2 thousand for a top end rebuild and carb tune.

Working on the bike is a bit difficult, I'm pretty experienced with mechanics, but I have limited tools where I live (always used my old man's tools, I'm slowly building up my own set), I have to leave my bike on the street, and I work nightshift, so I'm always sleeping when the best light for working on my bike is about, haha.

Well, sorry for the lengthy yarn, I just thought I'd give you blokes a bit of an idea on the background of my bike. Cheers, Benno.

No offense intended, but it sounds to me like you just want to pull the engine apart. :blink:

It's your bike, so tear it apart if that's your thing, but with the compression at 150/150/150/140 there is no reason whatsoever to replace the rings, regardless of you suspicions about oil (which seem totally unfounded - if the cylinders were full of oil the bike would have been smoking like mad!). Most likely you're compression will be worse rather than better after you replace the rings. Keep in mind that rebuilding an engine is FAR more challenging than removing jets from carbs, so if you had a problem with that the odds are the bike will never run again if you pull the engine apart. Broken stuff in there is REALLY expensive to have repaired!

There are many reasons why the engine may be running poorly, but with the compression level you measured rings is not one of the reasons.

Rather than simply throwing parts at the bike, which would result in wasted time & money and a bike that still runs poorly or maybe never runs again, I would urge you to take a more logical approach. If it was mine, I would start by performing a full tune-up; check valve clearances (as you mentioned), replace points, condenser, & plugs, change oil & filter, sync the carbs, etc. It seems obvious to me that the carbs are not tuned properly, and the fact that you damaged the carbs does not help. The previous owner installed pods and probably didn't have a clue or nearly enough patience to figure out how to rejet so the bike would run adequately. It appears that your bike may have CV carbs (I can't tell for sure) If it does I recommend you make a serious effort to find an airbox as those carbs are extraordinarily difficult to tune for pods.

Aside from the carbs being jetted wrong there are a number of ignition related problems and other issues that could cause the bike to run poorly. Why not test those system before getting into a very expensive ring job (even it you do it yourself rings, gaskets, etc are not cheap). Running diagnostic tests are free. Do you have a Kawasaki Service Manual? If so, use it to diagnose the problems the bike has; then you will know what needs to be repaired, replaced, or properly tuned. If you don't have the manual you really need to get one; no KZ owner should be without one.

I suspect my comments sound somewhat harsh, but sometimes there's no gentle way to present reality. I do wish you the best with your bike and hope you will accept the advice as it is intended to help you get the bike on the road rather than end up parting it out. Ed

All good man.

Forgot to mention, the bike is smoking...as in when I took it for a ride, you could follow me home by the smoke trail. I thought perhaps I could get away with it but I'd be pulled over in an instant with a machine that smokey.

Yep, it's got the CV carbs, and it was suggested to me by another person to hunt down a stock airbox for it due to the problems you run into with all the variables of pods. The jets in it at the moment are 37.5 pilots and 127.5 mains, the needle circlip was in position 2/5 (2nd highest position it could be in).

Don't take me as a rookie, I've rebuilt several bikes, my car's engine as well as a transmission swap, and helped my old man rebuilt the tractors on the farm. I didn't grow up in the city. Slightly rounding the slot of the pilot jet was because I used the wrong sized tool, which as you said, can be an expensive mistake when done to other parts.

The bike has been converted at some stage to point-less ignition, with the loom serviced and the coils, plug leads and caps replaced at the rebuild. I put new plugs in, all have a fat blue spark and have been gapped correctly. Compression, as I said, is fairly consistent. The valve stem seals were replaced in the rebuild by the PO. I haven't checked the timing as I need to borrow a timing light. I synched the butterfly valves in the carburetors before I put them back on, and turned the mixture screws to 1 and 1/2 turns from seated, just so they were all the same and I could work from there. I didn't adjust the float heights, I need to get a bit of clear tubing so I can see if they are at the correct spot. Not having a centre-stand anymore makes that a bit of a pain in the arse, haha.

Oil and oil filter is the next thing to buy, the oil seems very new and unburnt, but best to change it anyway.

I don't have a manual yet, I've tried to source one online but it seems the American models and mine is slightly different, I'll probably have to order a physical copy from the UK.

Thank you for your advice, my post makes it seem like I'm going about this more illogically than (I think) I am. Cheers, Ben.

Hi Benno
Ed always give very good advice. ..... And yes it does look like you have CV carbs. Well spotted Ed ! I wasn't sure if It was possible to have the larger CV carbs on a 650. A close up photo would be interesting
It's usually the simplest things which cause the problems. With the great compression you have opening the motor should be the last thing on the list
Good luck and welcome

One other suggestion - before you pull the head perform a leak down test. That will help identify if valves, valve seals, rings, etc. are leaking compression. I would not assume the PO replaced the seals or if he did that he used quality parts and did it properly.

Also, what spark plugs did you install? It is possible that the heat range is too cold (if you're lucky) and that could cause problems. Were the old plugs oil fouled? Ed

Thanks, JR. And yep, they're the Mikuni CV carbs, BS32s if my research is correct.

Yeah, the guy I bought it off seemed like a nice bloke, but that doesn't mean he did a good job. :lol:

NGK B7ES. The 4th cyl plug was a nice tan colour, the rest very petrol-soaked and are oily...although not as oily as I would have thought they'd be for the amount of smoke it's throwing out. The case breather pipe is clear and it isn't blowing, which I assume it would be if the compression rings were gone...

The PO gave me the receipts for the work done to the engine, the valves seats were reground, new valves, valve seals replaced, the barrel surface ground, the head hot chemical washed, new rings, all new gaskets from the barrel up (bottom end wasn't rebuilt).

My list now of things to do is valve clearances, oil, check the coils are getting full voltage, ignition timing, a leakdown test, the carburetors tuned, then go from how it's running then. Anything I've forgotten?

Thank you again for your advice guys, it's much appreciated.

The NGK B7ES plugs are the correct heat range. I asked mainly because the first edition of the KZ650 manuals listed the wrong plugs (too cold) as I learned the hard way. :laugh: :laugh: Ed

That's what I found out as well!

Well, I checked the valve clearances, several of them need to be shimmed, but none of them had not enough clearance.

A peculiar thing happened - I had the tank off and decided to see how long it'd take to use up the fuel in the hose and fuel filter. After I started it, it seemed to be running on at least 3 cylinders. To me, this suggests that perhaps the fuel level is too high in some of the carburetors, as after it had run for a bit, it went better than with the tank on? Or perhaps the tank is touching an electrical component and making it faulty.

God bless the PO for using Allen head bolts on the cam cover, it made it a breeze to take on and off.