stock 1981 kz550 - running lean lean lean

I'm thinking I have a carb problem.

1981 kz550, has 14k miles, have done this:
- pulled and cleaned petcock
- flushed gas tank with lacquer thinner, is not rusty at all, looks good and bare metal in there
- put in new spark plugs
- pulled and thoroughly disassembled all jets and carb bits and cleaned the carbs
- has healthy spark
- new battery
- timing advancer checked and working right
- runs very perky, real strong when I get on it, so I know it's getting gas.

But the plugs are bleach white.

The bike has stock everything.
- stock pipes
- stock carb jetting
- stock airbox
- all the emissions stuff is present

The only thing not stock on this bike are -- low, superbike-style handlebars.

The plugs should be golden brown.

IT PINGS LIKE A MAD DOG at idle.

It pings so loudly it sounds like you're listening to helicopter blades chopping the air if you know what that sounds like.

I don't think the fuel supply from the gas tank is not working -- I can open the drain plugs of each carb's float bowl and gas is coming out. Also, when I give it gas, this bike really goes.

It's just super-lean, and I know these were set up to run a *bit* lean when new, and yep it is in 100% stock configuration -- but it shouldn't ping.

It's detonating I think. Plugs are scary white.

Any ideas?

I forgot to add -- I do *not* think I have an air leak.

I don't have a 'racing' idle. I can rev the motor and it comes back down immediately to my 1100 rpm idle that I set with the thumb screw.

If it was an air leak causing the lean condition, the bike would hang at higher rpms after I rev it while it's in neutral and on the centerstand in my driveway, back wheel off the ground.

But it returns quite normally back to idle after I rev it up -- so no air leak to explain the scary white spark plugs.

Do you have any older plugs to check the lean condition with? I'm wondering if the pinging your hearing is spark energy leaking out of the sparkplug wires/coils.

I had the pinging/knocking yesterday, as well as crummy-low weak power, and this morning I did a couple things to try to resolve those 2 issues:

1) new spark plugs

2) check timing advancer


Fixing the timing advancer pretty much took the bike from a skateboard to a Ferrari in terms of power. It really gets up and goes, except it stumbles immediately when I'm moving up from idle, I have to open the throttle more than I should but then it gets up and GOES. So the advancer was causing the poor power problem.

But the pinging did not go away. I'll put the old plugs back in, but I suspect there's something else going on. I did notice my fuel levels in all 4 carbs were a bit low when I checked them all about 1 1/2 hours ago, but I don't think a low fuel level in the bowls will make the plugs scary white and make it ping/pre-ignition/detonate.

Click > www.kzrider.com/forum/2-engine/451273-my...ncer-is-blown#451368

That will be the first thing I check this morning, thanks Patton.

I chased down and found/fixed the frozen advancer yesterday, and it helped a lot -- question for you,
if the timing is off ('F' mark not aligned), the pinging I still have would make sense --
but would that also bleach the spark plugs, making it appear the bike's running too lean?

If your ignition timing is off it can cause the engine to run too hot and make white plugs. Also, what octane gas are you running? Higher octane fuel helps reduce pinging but should not be considered a substitute for proper tuning. Ed

After Downloading the manual from loudvhx, did you verify All of the jet sizes? Have you checked the fuel Level with a clear tube? If the level is low it will lean the carb through out its range as it will be harder for the same amount of venturi signal to pull fuel. similarly to high will make it easier and run rich. Also when your advancer was stuck, did you apply heat with the springs still attached? Could they have heat stressed and stretched? Although that doesn't explain pinging at Idle, i don't think I've ever heard an Ignition, or lean carb ping at Idle. Maybe also verify that the Timing mark is at the 10 degrees BTDC as maybe your not on the pin where the advancer goes on the crank? Just a quick mechanical verification, you could check the TDC mark to see if it is true.
Have you done a compression test or leak down test to see if it may have mechanical damage? As that much pinging can cause broken piston rings and lands.

Motor Head wrote: After Downloading the manual from loudvhx, did you verify All of the jet sizes? Have you checked the fuel Level with a clear tube? If the level is low it will lean the carb through out its range as it will be harder for the same amount of venturi signal to pull fuel. similarly to high will make it easier and run rich. Also when your advancer was stuck, did you apply heat with the springs still attached? Could they have heat stressed and stretched? Although that doesn't explain pinging at Idle, i don't think I've ever heard an Ignition, or lean carb ping at Idle. Maybe also verify that the Timing mark is at the 10 degrees BTDC as maybe your not on the pin where the advancer goes on the crank? Just a quick mechanical verification, you could check the TDC mark to see if it is true.
Have you done a compression test or leak down test to see if it may have mechanical damage? As that much pinging can cause broken piston rings and lands.

Thanks MH, good calls there.

My compression is from 1 to 4, 152/152/148/152 so, at least for now, I'm still good, and I don't really want to drive it anymore until I sort this pinging for the risks you mentioned.
I don't think I have the right tools to do a leak-down, all I have is my compression tester gauge.


I didn't use heat to free up the advancer -- I let it soak after drenching it with PB Blaster then gripped the non-moving part, and lightly rotated the rotor and it broke free.
When I re-installed, I was careful to purposely mis-align the groove on the back of the advancer and the pin on the crank end -- then I moved the advancer until I felt the groove match up with the pin. Did that twice.

My fuel levels are a bit low, between 5 to 7mm low. What I mean is, the manual calls for a 3.5mm clearance and I've got 10mm/8mm/11mm/11mm levels from 1 through 4, while the manual says the fuel levels should be 3.5mm/3.5mm/3.5m/3.5mm.

HOWEVER -- the caveat is I discovered after checking the levels that putting the bike up on the centerstand was not quite enough, I was supposed to 'block up the front wheel' so that the carbs were level. So my fuel levels check yesterday with carbs on the bike was in my opinion a bit sloppy.

After checking the timing today, I'm going to pull the carbs and bench test the fuel levels again.

I will check the jets once again too. I don't know the 'location history' of this bike -- I am wondering if it was jetted for a high altitude (I'm at sea level) -- maybe it's got leaner-than-stock jetting. This bike is so completely stock, I just assumed the prior owners didn't change the jetting. The original owner was an old guy who parked the bike over a decade ago after putting only 14k miles on her. I then bought it from his grandson who got the bike as inheritance and never rode it.

So I just assumed his grandpa, having left the rest of the bike 100% stock, well the last thing such an owner would mess with is carb jets, no need to, has stock pipe and airbox and emissions cannister. *Unless* it was jetted lean at the shop when he bought it due to high altitude. Just a swag here on my part, but I'll check when I pull carbs again.


I don't completely trust my 10mm/8mm/11mm/11mm fuel levels that I read on the bike yesterday.

I've got the manual and I'm going to use my meter to check the pickup coils, and will also thoroughly check timing. If they're ship-shape, the carbs are coming off again.

That compression sounds good. And I think that you are on a good track going to pull the carbs for Benching. Could be just as you say, a High Altitude Jetting when sold new or soon after.

Also what fuel did you put back in it? There has been a rash of lower than advertised Octane fuel at these cheaper stations, as much as 3 points lower.
Good luck getting those carb boots on and off, PITA! But they run good with the Airbox.
After install verify no Air Leaks at manifolds.

650ed wrote: If your ignition timing is off it can cause the engine to run too hot and make white plugs. Also, what octane gas are you running? Higher octane fuel helps reduce pinging but should not be considered a substitute for proper tuning. Ed

I'm running 87 octane and I normally don't do that with my bikes, I generally run super (91 octane here in California) but I wanted to hear this guy run so I went with my lawn mower gas can which is 87.

Thanks for pointing out how mis-timing can result hot running -- when I turn the engine off after a ride, it does not crackle or pop a lot like a turbo'd motor does, but it definitely seems too hot for the short test rides I've taken in the past couple days.

The only thing that puzzles me about the timing setting on this bike is -- the bike (1981 kz550-A2) came stock with electronic ignition, not points/condenser, and the f.s. manual says 'the timing is not adjustable' and I took the plate off yesterday that has the pickup coils -- had to remove it to get at the ignition advancer -- and I did not notice any adjustment possible for that plate, the holes where the plate attaches to the engine are big enough only for the screws, it didn't appear that the plate with the pickup coils can be moved around to alter the timing.

Also, the timing advancer doesn't seem adjustable either -- it fits onto a pin on the crankshaft then you tighten its one bolt to lock it down, the bolt that screws into the end of the crank.

I'm going to check the timing marks etc. today, but even if they're off, I have to admit I don't see how I can adjust them.

What is the #'s on the Spark plugs? Correct heat range? NGK or?