KZ900 opinions please

My KZ900 is nice to ride, it's not particularly fast though. I checked the compression and here are the readings in order of cylinders.

122, 105, 115, 115

I poured motor oil in cylinder #2 and it didn't change the compression.

Also used the morgan carbtune to check the mixture at low rpm's.

I checked the ignition timing (dyna S) and it's okay. Also checked the ignition advancer and it seems to be working fine.

The bike doesn't idle well after first firing up, I can turn up the idle to keep it from dying but then when the motor is warm it idles too high and I adjust the idle down. I bench synced the carbs, have not synced them with gauges yet, will probably do that next.

It has a 4 into 1 pipe, stock airbox with K&N, stock 26mm carbs, pilot jets 15 mains 117.5 needle on middle clip.

The bike looks great and I'd probably like to keep it. I would rather not spend the money for a rebore because I have many other motorcycles to work on. And if I decide to sell this one I don't think I'll get the rebore money back in the sale price. So I'm thinking maybe take the head off and get a valve job by a local mechanic (he's experienced, I know him well). Then maybe get new piston rings.

Will new rings and a valve job put enough life into this motor? If I get it rebored I might have to send the block to the U.S. mainland because the shop that used to bore motorcycle cylinders here closed about a year ago and the local auto shops I called say I have to bring the block in to see if they can bore it. Not confidence inspiring.

Resident experts please let me know what you think.

Thanks, Mike

sounds like you know a bit about bikes.

did you have throttle wide open on compression check? if not you will get incorrect numbers.

how many miles are on bike? you might do good with a valve job and valve seals.

Those 26mm carbs are very small a restrict the bike.

You would notice a nice bump with a set of 28mm carbs.

Before even considering opening up the engine - here are my suggestions:

- Check the valve clearances and adjust if needed.
- Test for carb holder leaks. (let us know if you need instructions) Leaky carb holders absolutely ruin idle smoothness. If there are leaks replace the holders.
- Test the fuel level in the carb bowls using clear tube method and adjust if needed. (let us know if you need instructions)
- Synchronize the carbs using quality gauges or carb sticks. Bench synching will only get you to the ballpark; it will not ensure equal vacuum pull across all carbs.

Ed

The odometer says 18k miles. I held the throttle wide open when I checked compression.

All four carb holders were replaced when I fixed up the bike a couple of years ago.

Fuel level might be a problem. I have an extra float bowl and I think I'll turn it into a fuel level checker.

I think the next step will be to sync the carbs. I don't think that's going to add much power though, hopefully it will smooth out the idle.

Make sure the valve clearance is set correctly. If this has been neglected it's very possible the clearances are non-existent.

Also, if the bike has been sitting a while, it's best to get the engine through a couple of heat cycles to free up piston rings as they can gum into the ring grooves.

If the engine has not been apart, it's worth running some SeaFoam or Ring-Free through the fuel for a tank or two - this can help free the rings and also remove carbon on the valve. ...and recheck the valve clearances AFTER 100+ miles of running the SeaFoam or Ring-Free through the engine.

This sounds very much like my KZ900. The compression is very similar. I think the standard compression on our bikes is 140 or 145 with a service limit of 95. A 14 psi max difference is allowed between the highest and lowest cylinders. Having said that, as long as you get it running smoothly with good pull then you should be happy. I for one, think that mine is slow enough not to get me in trouble., LOL, But fast enough for a thrill. What Ed and Jeff described is the way to go. I did the same exact thing. Here is what I found with mine; I made sure my valves were within tolerance. A valve with no clearnce will cause you to lose some compression. I knew my boots were ok. My pilots are 20 and my mains 118.5 or something like that. But I have the 4 to 1 and pods. After, I set the float levels. This is critical. I adjust my fuel mixture ( seems to like it rich at about 1 turn out) and synced them up. I'm sure, due to the low compression, my bike is probably at about 75% or less in power. But going WOT is still enough to overtake most of the cafe bikes I ride with. On the highway at 75 mph, all I need to do is crack the throttle a 1/4 turn and it will pull to ninety in a snap, 90 catches me by surprise .I end up having to back off. Even at lower rpms, as long as the rpm is at least 3000 rpm, on lets say 4th gear, no need to gear down. Just crack the throttle and she'll pull. Can't justify a rebore and head work for $700.00 to get it at 100% right now Sure, the difference between highest, and lowest cylinders just like yours, is beyond the 14 psi difference that is allowed as per service manual. If you can get it to run nice and smooth, maintain idle with adequate power, than I would just enjoy it as is. After getting all the main adjustments done, I found playing with the air mixture screw to fine tune it was the trick to getting the idle right. Good luck.

Thanks for the additional inputs. I checked the valve clearances and changed a couple of shims within the last six months. The carbs were cleaned and I put seafoam in the tank periodically. I just added some seafoam to the crankcase when I changed the oil recently.

Joe, you're right our bikes sound similar. My KZ900 runs great on the highway, street manners are okay too other than the idle fluctuation from cold engine to warm. My '78 KZ1000 more fun to ride though, it just has more grunt on the bottom end.

I recently fixed the fuel level on my H2. I had the float levels adjusted per specification but the bike didn't run well on the bottom end. A clue was that two carb bowls leaked fuel at the gasket. So I adjusted the floats to get the fuel levels lower. That made a great improvement. H2's don't have a drain screw on the bowl so I don't know what the fuel level is, but the bike's performance is much better.

I have a spare float bowl for a KZ and will hookup a clear hose to it, then check the fuel level for each carb.

Sounds to me like you are having carb problems more than any thing else. Clean carbs and good carb boots. A weak spark can cause the bike not to want to run well. One place to check is the wire ends where the caps screw in for corrosion. One can snip a little of the wire back and screw the caps back on.
What do the plugs look like?

Plug #3 is sooty. The other three look about the same, tan colored. The bike has emgo coils.

Kapahulu wrote: Plug #3 is sooty. The other three look about the same, tan colored. The bike has emgo coils.

If you screw the air bleed screw in or out on #3 carb, any RPM difference? On my Z1 it's #2 giving me a hard time with a sooty plug with the other 3 burning clean. (light tan) I'm going to clean the snot out of carb #2 and see if anything changes.

Last time I sync'ed the carb's I could screw #2's air bleed all the way in or out with no RPM change. the Bike ran good though. I would rather have a rich situation rather than a lean one.
I should recheck the float level on #2 for grins.

Best, Tim

It's hard to tell if there's any rpm difference because the idle drops off sometimes. I used the Gunson Carb Tune last week to adjust the air screws.

Leakdown test performed...?

All it takes is little carbon on the valve seats and she won't close all the way thus lower compression measurements. Simple Valve seat lap can clean this up.... Lapping tool and compound at any auto parts store...

As for performance..... carbs, ignition spark/timing, valve clearances, electrical spark can all be associated to under par performance / expectations. Normally with a vacuum leak, she'll pop on ya...

Another review for rich/lean, condition of plugs (base ring, strap, porcelain)....?

Regarding the Morgan color tune, you perform all 3 adjustments/verification's and they came out right...?