intermittent not firing on cylinder #2, 78 Kz1000

1978 kz1000 A2 model. It has a Gerex electronic ignition.

I just did a valve adjustment and bumped up the main jets due to a Kerker 4-into-1 and a modified less restrictive airbox (the prior owner did the airbox and pipe and didn't rejet and it had been running lean).

Now the plugs look golden brown and lots of power except cylinder #2.

Okay, I also changed oil and filter and overfilled it with oil so much that I had plugs fouling and oil dripping out of my carb's float bowl overflow rubber hoses (the 4 rubber hoses that connect to a nipple at the bottom center outside of each float bowl and are routed between the front of the swingarm/rear of engine to drop excess fuel the ground). Oil was coming out of all four carb overflow tubes, and I found oil in bottom of the remnants of the stock airbox. There was too much oil in the crankcase and it got deposited via the crankcase breather hose into the airbox.

I removed the excess oil and cleaned the airbox so it's free of oil.

Plug #2 is firing only intermittently, the rest of the cylinders are fine, and plugs for #1, #3, and #4 are golden brown so I know I have the jetting correct.
Plug #2 is black with soot. However, the #2 pipe gets HOT and there is so much power when I'm on the mains, even with cylinder #2 dropping off intermittently, that I KNOW cylinder #2 is firing somewhat frequently.


Also: it doesn't matter if the carb circuit in use is the pilot circuit (to 1/4 throttle), or the needle (up to 1/2 throttle), or the main jet. I can hear that Cylinder #2 is not consistently firing in each of these 3 'zones of operation' of the carb.

I'm going to switch plugs #1 and #2 and see if the intermittent firing problem goes with the plug to cylinder #1.

Any other ideas? I'm wondering if there is still a ton of oil in the #2 float bowl and it's fouling the #2 plug, although I kinda doubt it as I put about 20 miles on the bike to burn off the oil-laden gas that got into the carbs.

Do change the plugs and see what happens. You could also change the plug wires between 2 and 3 and see what happens.

Okay, so I swapped spark plug #2 into cylinder #1 and took it out for a run. Since I had previously found the spark plug from #1 was fine, it was a golden brown color - I thought that if cylinder #2/carb #2 etc. had some problem that was making the #2 plug sooty and black, my known-good #1 plug that was fine in cylinder #1 would get very sooty after I put into cylinder #2.

When I pulled the known-good plug from cylinder #2 after my run -- it was still golden brown! So I thought "Wow, excellent, there never really WAS a problem with cylinder #2 -- it's running fine once I put a known-good spark plug in there."

Naturally, the old #2 plug that I put into cylinder #1 -- well surely it was still going to be black and sooty. NOPE. It was fine too!

So I pulled the plugs from #3 and #4. FINE. Yet the kz1000 just doesn't *sound* right.

I then put all 4 plugs back in, they all were golden-brown, and took the bike for spin. Now the damn bike is popping/backfiring/misfiring intermittently (I haven't pulled the plugs yet, too disgusted, will do it tomorrow).

So I have a list of things I'm gonna check:

1) is the battery charged up? And is the charging circuit putting out 14v at 2000rpm?

2) I may have some oil that's still sitting in the carbs from my oil-overfilling mistae. I'm gonna pull the carbs and clean 'em.

3) check the valve clearances again. I had just finished checking them and had to install 2 new shims to get all the clearances in spec. I'm going to check again.

4) my final suspicion is the Gerex electronic ignition. The prior owner took out the stock points/condensers and put in a Gerex electronic ignition in this '78 kz1000. This Gerex is about 30 years old based on what the bike's 1st owner (who I bought the bike from) told me.

I think 30 years is pushing it for an electronic ignition, especially since the bike sat under a tarp, never used, in first owner's back yard for about 12 years before I got it. Lots of moisture exposure is evident on the bike, nothing super-bad but I just can't think of a single electronic component I have owned for 30 years. Most electronic components are history in 5 years or less.

I'm sure that Gerex used state-of-the-art electronics back in 1980 when my prior owner bought this ignition -- but 30 years may as well be a century with technology components.

I wish I knew some way to *measure,* not simply look at, but *measure* the voltage of the spark at the plugs.
Because I'm wondering if -- maybe I'm getting intermittent weak spark from this 30-year-old Gerex ignition box.

Any of you have any suggestions to help me find this intermittent not firing/misfire/backfire issue?

I had a Dyna III and my bike was doing the same thing. It would drop a cylinder intermittently. The problem turned out to be in the box ignition itself. I swapped the Dyna III for a Dyna S that I was given with the bike and the problem was solved.

Thanks, I believe a new box could well solve my problem.
I really find it hard to believe that a 30-year-old electronic ignition box works at ALL.

Do you know of a 'spark plug voltage meter' available? Are there digital multimeters or some sort of 'spark plug voltage reader' tool you can buy? I really want to be able to read a voltage level on the plug gap to assess how strong/weak the spark actually is. Relying on the 'brightness' or 'dimness' of the spark itself is inexact and a weak way to accurately assess the health of the spark gap peak voltage.

newOld_kz1000 wrote:

...Do you know of a 'spark plug voltage meter' available? Are there digital multimeters or some sort of 'spark plug voltage reader' tool you can buy? I really want to be able to read a voltage level on the plug gap to assess how strong/weak the spark actually is. Relying on the 'brightness' or 'dimness' of the spark itself is inexact and a weak way to accurately assess the health of the spark gap peak voltage.

A coil tester is the closest method I know about.

Good Fortune!

[Click on image to enlarge view.]

Patton wrote:

newOld_kz1000 wrote:

...Do you know of a 'spark plug voltage meter' available? Are there digital multimeters or some sort of 'spark plug voltage reader' tool you can buy? I really want to be able to read a voltage level on the plug gap to assess how strong/weak the spark actually is. Relying on the 'brightness' or 'dimness' of the spark itself is inexact and a weak way to accurately assess the health of the spark gap peak voltage.

A coil tester is the closest method I know about.

Good Fortune!
/quote]

Thanks dude, I wonder if I could find a general purpose version of that Kawasaki tester -- I'm going to check tomorrow and will post back if I find one. I bet the Kawasaki tester is great but not cheap. Maybe something similar is out there that's mass-produced and thus more affordable -- I will let folks know if I find one.

Well the popping/misfiring is FIXED, I accidentally jammed the spark plug against something in the low-light conditions last night and didn't notice the spark plug gap got reduced to almost nothing. Today when I looked at the plugs I found that -- so I regapped that one plug and no more misfiring.

Now this bike runs strong and wants to pop a wheelie.
Plugs are golden brown.

BUT IT SOUNDS LIKE A 4-STROKE LAWN MOWER ENGINE. It just does NOT sound like its 100% consistently firing all cylinders. Despite the power.

Got me to thinking. This kz1000 is pulling really hard, scary hard actually -- and all I've done is bump up the mains from 105 to 120, the pilots from 15 to 20, and lowered the clip on the needle 1 position (hence raising the needle). This scary power (I mean the bike feels like its gonna rip away from me, I'm literally hanging on for dear life) -- with the prospect of it still not running correctly -- got me thinking about the prior owner's comment that it had been bored out and had hot cams in it.

Because of the fact that my 2nd bike was a '77 kz1000A1, bought new in 1977 when I was 17yo, I *know* how these kz1000s feel. This kz1000 '78 is crazy and I now am starting to believe what the prior owner told me about the cams/bored out.

So here's my question: I did my valve adjustment PER THE FACTORY SHOP MANUAL.

Is it *possible* my valve clearances need to be measured differently from the procedure in the factory manual?

And is it common with hot cams for these bike that the clearances are different from the factory specs?

And could that be why the motor sounds so funny to me.

If the motor's still not running right (it sure sounds funny, like a lawn mower) then it will be very hard to hold onto under acceleration once it's put right.