stock 1981 kz550 - running lean lean lean

sorry i just refreshed the page and saw where you said it sounds lower. the way you explain it really makes it sound like the cam chain though.

Sounds like you need to synch the carbs and then adjust the idle to 1300-1400.

You can see some color starting to develop, maybe they just don't have enough miles yet. Even plugs in a closed loop fuel injected computer controlled gas engine gets plug color, also on LPG/ propane.
Did you also check the jet sizes against the FSM?
Does that noise your hearing change when tilting right or left? Does it get louder if you set the Idle down a bit to say 900? Then you may be able to hear it better to source it. Do you have some extra fuel line, or another hose section to hold to your ear? Try to source where it is.

mjg15 wrote: Sounds like you need to synch the carbs and then adjust the idle to 1300-1400.

The carbs could well be out -- but probably only the #3 carb. If you read on the first page of this post, the prior owner was a big guy who, when confronted with the throttle not moving (carb slides stuck from sitting) he twisted the throttle so hard it broke the retaining screw for the #3 carb slide lifter.

I had to disassemble the #3 carb slide lifter to repair it then I eyeballed the sync during reassembly. There's only one long rod that runs through all 4 carbs -- the rod rotates and lifts all 4 slides in unison. That rod forces all 4 slides to open at the exact same time -- I can't seen any 'slop' possible in the linkage that would allow one slide to open first.

However -- it is highly possible for my #3 slide's bottom gap (when the slides are resting) to be larger. I eyeballed that on the #3 carb when I reassembled -- I tried to make the gap between the bottom of the slide and the carb throat match the other 3 carbs. Did not measure it though.

I didn't know the bike might be so sensitive to one carb 'leading' the other 3 carbs by being open a bit more.

I'm trying not to yank them carbs again man I'd rather watch my dog take a dump.
Looking like it might be unavoidable here.

The higher the idle is the less you hear the chunk chunk, right now it's set at 1500 so no one feels bad for me at stop lights. Seems like everyone's a bike mechanic at stop lights "Hey your engine's knocking."


I guess it is possible that after sitting for 20 years, the cam chain tensioner is stuck.
When the carbs come off I'm going to yank it and have a look at it. I went to adjust it like
you do on a Z1 or Kz1000 motor but by 1981 the Kz550 came with an automatically adjusting
cam chain tensioner.

I'm hopeful that the primary chain is not the source of this noise.

Motor Head wrote: You can see some color starting to develop, maybe they just don't have enough miles yet. Even plugs in a closed loop fuel injected computer controlled gas engine gets plug color, also on LPG/ propane.
Did you also check the jet sizes against the FSM?
Does that noise your hearing change when tilting right or left? Does it get louder if you set the Idle down a bit to say 900? Then you may be able to hear it better to source it. Do you have some extra fuel line, or another hose section to hold to your ear? Try to source where it is.

I'll use a listening tube (gas line) and find where the noise is loudest today.


The noise gets scary loud at 1000 or 900 rpm, sounds like the motor is about to break.

When I pull the carbs I'm going to check jets against FSM, I skipped that before due to the nature of the old man who owned it who kept it bone stock.

I know these bikes were set up way lean to pass EPA in California. If the FSM shows bigger stock jets as an option for the pilot and mains I'm thinking about going up 2 sizes each on the pilots and the mains. The FSM for the U.S. bike (Table 1 page 68) shows 32 pilots and 92 mains.

The noise gets much quieter when I pull in the clutch (bike in neutral, just pull in the clutch lever and the chunking noise gets quieter) -- why would that be?

There is a screw and locknut on top of the slides that you use to synch the carbs. It is very sensitive. Somebody forcing the slides open could easily affect the synch. The carbs come out pretty easily with new airbox boots, but you don't have to remove them to synch the carbs, however you will need a manometer type synch tool. If you want a perfect running 30 year old bike there are no shortcuts.

In order:
-verify valve clearance
-verify compression
-clean carbs/verify jetting
-verify function of advance mechanism
-verify no vacuum leaks at manifolds
-synch carbs @ 2000rpm, and check again at factory idle spec rpm

It seems like you've done some, or most, of these steps, but if you don't do all of them you are relying on luck.

And I'd reccommend doing ALL of them, in order, before going on a wild goose chase thru the clutch, starter, etc. I've had a dozen 550's over the years and I've never replaced any clutch or starter parts.

mjg15 wrote: There is a screw and locknut on top of the slides that you use to synch the carbs. It is very sensitive. Somebody forcing the slides open could easily affect the synch. The carbs come out pretty easily with new airbox boots, but you don't have to remove them to synch the carbs, however you will need a manometer type synch tool. If you want a perfect running 30 year old bike there are no shortcuts.

In order:
-verify valve clearance
-verify compression
-clean carbs/verify jetting
-verify function of advance mechanism
-verify no vacuum leaks at manifolds
-synch carbs @ 2000rpm, and check again at factory idle spec rpm

It seems like you've done some, or most, of these steps, but if you don't do all of them you are relying on luck.

And I'd reccommend doing ALL of them, in order, before going on a wild goose chase thru the clutch, starter, etc. I've had a dozen 550's over the years and I've never replaced any clutch or starter parts.

Thanks man, it is highly appreciated to hear from a kz550 owner especially the part about never needed to worry about clutch or starter parts.

I decided to forgo the valve clearance check due to the low miles (14k) but this morning I figured there's not much else I haven't checked and started to consider doing it despite the low miles.

Part of not wanting to pull the carbs is -- once you're spoiled on it it's hard to go back. I have a 1998 Suzuki 600cc-4 (GSF Bandit) and did the carbs 2 weeks ago on it. Those Suzuki frame designers did a good job. On my 600 you loosen loosen 2 screws and the black airbox and boots slide way back out of the way. It was so easy to remove the carbs on the 600.


I'll have to pull them and I'm going to check valve clearances too, I'll do WD-40 on the intakes but with no 'high idle' leak symptoms it probably will not show anything.

The noise is so prominent it would not surprise me if the automatic cam chain tensionser got stuck during the bike's 20 year of sitting; then when the grandson of the old owner inherited the bike 2 months ago, the cam chain loosened up and the tensioner is stuck from sitting and didn't take up the slack. Something like that.

I'm thinking it's a synch issue, due mostly to someone strongarm'ing the throttle mechanism. Like I said earlier, the carbs are very sensitive to synch adjustments. You may try popping the cap on the #3 carb and moving the adjuster screw both ways (with engine idling) to see if it improves. It's not nearly as good as doing it properly, but since you mention damage to #3 that could've caused it to go way out of adjustment, it may be a good place to start.


FWIW, You can get the cam chain tensioner out while the carbs are in place, but it takes a bit of patience.......you do have to move the carbs though. Loosen the front clamps, pull the carbs back til they pop out of the manifolds, and then set the front of them on the tops of the intake manifolds.

The knocking. clunking is more than likely due to an uneven running condition between cylinders. A lot of things can cause this to be the case (pretty much everything on my list).

With the compression readings that you have your valve adjustment is probably OK.

mjg15 wrote: I'm thinking it's a synch issue, due mostly to someone strongarm'ing the throttle mechanism. Like I said earlier, the carbs are very sensitive to synch adjustments. You may try popping the cap on the #3 carb and moving the adjuster screw both ways (with engine idling) to see if it improves. It's not nearly as good as doing it properly, but since you mention damage to #3 that could've caused it to go way out of adjustment, it may be a good place to start.


FWIW, You can get the cam chain tensioner out while the carbs are in place, but it takes a bit of patience.......you do have to move the carbs though. Loosen the front clamps, pull the carbs back til they pop out of the manifolds, and then set the front of them on the tops of the intake manifolds.

The knocking. clunking is more than likely due to an uneven running condition between cylinders. A lot of things can cause this to be the case (pretty much everything on my list).

With the compression readings that you have your valve adjustment is probably OK.

I would tend to agree about the valves, but if what I'm doing next has no effect, they're next.

I pulled the carbs and will get to them directly. First, I wanted to check that cam chain tensioner. As it turns out, the factory shop manual has a warning (paraphrasing here):

"Early 1980 Kz550s had cam chain noise due to a bad cross wedge spring, the corrected spring
is 46.2mm long, the bad spring is 53.2mm long, the longer spring was too weak, get the correct spring from your dealer" and I thought 'ah hah' even though the fsm said it was only on the 1980
kz550.

So I measured that 'cross wedge spring':



LOOKS OKAY, IS 46MM LONG. Well that's not the noise source -- unless the cam chain tensioner was installed wrong before, which is certainly possible -- there is a specific order of assembly that must be adhered to. Maybe it was installed incorrectly before.


The cam chain tensioner looks okay.




So now it's on to the carbs.

Well, as long as the carbs are off you may as well bench synch them (do a search if it isn't in the manual, and pop off the intake manifolds and put a thin coat of sealer between them and the cyl head.


If you remove the manifolds be aware that the screws are not phillips, and that the heads of the screws could strip if you use a phillips bit. They are JIS, you will need to grind the pointy tip off a phillips if you want it to work properly.

mjg15 wrote: Well, as long as the carbs are off you may as well bench synch them (do a search if it isn't in the manual, and pop off the intake manifolds and put a thin coat of sealer between them and the cyl head.


If you remove the manifolds be aware that the screws are not phillips, and that the heads of the screws could strip if you use a phillips bit. They are JIS, you will need to grind the pointy tip off a phillips if you want it to work properly.

The manifolds look great, so I won't remove them, but thanks for the tip on the screws.

On the #3 carb the slide at fully down/resting position had about 2 times the gap of #1, #2, #4 carbs. I'm going to correct that.

But we're talking the #3 slide open only a bit more than the other 3 slides -- as I look at the carb throats, unfortunately I can't find my caliper but it appears the open gap of the throttle slide to the bottom is 2.5mm on #1, #2 and #4, while the gap on #3 is about 4mm -- would that cause a loud muffled knocking, like the sound a Z1 or Kz900, Kz1000 engine makes when you take it off the choke before it's warmed up enough? I just find it hard to believe that one carb 'leading' the other 3 carbs would cause such a loud chatter. You can hear it from over 10 feet away, 'something's wrong with that engine' type of deal, when it's at idle -- it's that loud.

Is it possible?

Uh... yes. :laugh: That much difference in slide height is massive! It can sound like you've thrown a rod bearing :laugh: ClangClangClangClangClangClangClangClangClang! :laugh:

You really should invest in a Carbtune, or a set of good vacuum guages designed for carb tuning.

The difference (of slide height/throttle body opening) between a few hundred rpm difference of cylinders across four carbs is barely visible to the naked eye.

Good luck! - in the mean time, bench sync with a piece of metal coat hanger, or houshold wire, or drill bit... you get it. Something rigid that will yield the same result across all four for now.

Vacuum syncing isnt getting all four slides exactly the same, its getting the amount of vacuum drawn in the same, which means the slides will all be different heights, but just barely visibly.

Accuracy is a must!

YO. Sorry to laugh at your expense... hope I can help really :whistle: