no more guesses - can't figure it out

It may be possible that a fouled plug would lower the voltage on that plug wire, possibly dropping the voltage below the detection limit for the light.

You had the same problem both before and after installing new plugs?

Is the misfiring plug wet with fuel?

Sounds to me like the ignition system is fine, so I'd move on to checking the fuel level in the float bowls.

steell wrote:

#1: Fired totally normally, with a flash as expected
#4: Misfiring often, missing lights about 3-4 times a second.

1&4 are on the same coil, and it's one circuit, you can't have spark on #1 without also having spark on #4, the spark plugs are in series.

I didn't realize that, I thought they were in parallel like the dual coil on my 750 twin. I'm not sure I understand how a series connected set of plugs works.

Alright, I think I am one step closer to an answer. I tested the float bowl level of all the carbs, and it was perfect.

I yanked the carbs off the bike and went to blow some carb cleaner through the pilot idle circuit. I doing so I could see not everything was right. So I pulled the fuel/air adjustment screws out of each carb in turn.

#1 had the oring and washer in the wrong order.

#2 had no oring.

#3 was as it should be.

#4 had the oring in fragments, on was mostly blocking the idle pilot hole to the carb throat.

So I went to the hardware store and no one had an oring or washer that looked right. Rather than mess around, i called the local dealer and order 4 new orings and 4 new washers. will be here thursday.

So the bike is no-go until thursday, but I have a feeling this messed up idle screws were a part of the problem.

If there are any more useful ignition tests I can run while the bike is not running let me know. Otherwise, I'll see if properly installed washers/orings fixes this stuff.

bountyhunter wrote:

I didn't realize that, I thought they were in parallel like the dual coil on my 750 twin. I'm not sure I understand how a series connected set of plugs works.

Brief thread hijack

750 twin plugs are in series, just like the diagram I posted above.

End thread hijack.


Back on topic.

I think your ignition system is fine, you have electronic ignition and have verified the coils/wires/caps/plugs are good, and the rest of it either works right or don't work at all, so you're done with that part

Time to start thinking about GPz750 cams and a 810 kit now :laugh:

no joke - the leakdown test was a way to see if I could wait until winter for the 810 kit or if i had to be done now...

If the engine runs fine when you give it throttle I would say your carbs are out of synch. That will give you a very rough idle and a knocking sound due to the primary chain slapping around because the cylinders are not firing at the correct time. As far as the white smoke. Does it get worse as the engine warms up or does it go away. I have had air cooled bike smoke a lot after I take them out of storage and fire them up. The smoke goes away after the engine warms up and a good ride.

alright, so the new o-rings and washers came in for the pilot mixture screws. installed and #4 sounds a bunch better.

however, #2 still doesn't seem to be firing at idle. i swapped the coil wires again, and the problem remained at #2 - #3 continued to fire fine.

So the fact that I have white smoke pouring out of 1/2 exhaust and #2 doesn't fire, what more tests can I do that i haven't already done above?

dnpurdy wrote:

...#2 still doesn't seem to be firing at idle...So the fact that I have white smoke pouring out of 1/2 exhaust and #2 doesn't fire, what more tests can I do that i haven't already done above?

Don't recall yet seeing actual compression test max psi figures (in addition to the leakdown test results). Remember to hold throttle wide open during compression testing.

And what about the earlier suggested floatbowl fuel level tests? Use the clear plastic tube test with carbs still on bike and fully assembled. If level adjustment is indicated, the float tangs may be re-set with carbs on the bench. And levels re-tested on the bench before reinstalling them. (More about that later if desired).

Would also replace #2 with brand-new sparkplug, because existing plug is by now likely fuel-fouled beyond recovery.

And set all pilot adjustment screws to the initial default setting per FSM specs.

If problem persists with decent compression, and assured correct floatbowl fuel levels, and equal pilot screw settings per FSM specs, and brand-new #2 sparkplug, likely should next consider problem in carb pilot circuit.(More about that later if desired).

Also, please confirm the carbs having pilot fuel mixture screws on bottom of carbs, and not side-located pilot air screws.

Thanks -- and Good Luck!

Alright, yes i haven't done in actual COMPRESSION test, this is true. I guess the leakdown doesn't give all the same information - I only showed it can hold 50 psi, not 150.

I have done a float level test with clear tube, and all are right on at 4mm below float bowl mating surface level.

I will get a new plug tomorrow and rent a compression tester.

The mixture screws are all set at precisely 2 turns out as per spec. The are Keihin CVK34 carbs with fuel mixture screws on the top, just after the throttle butterflies just before the intake manifolds.

Actually, there is a Murray's open for the next 2 hours...going to get plugs and tester now!!!

dnpurdy wrote:

...have done a float level test with clear tube, and all are right on at 4mm below float bowl mating surface level. I will get a new plug tomorrow and rent a compression tester. The mixture screws are all set at precisely 2 turns out as per spec. The are Keihin CVK34 carbs with fuel mixture screws on the top, just after the throttle butterflies just before the intake manifolds. Actually, there is a Murray's open for the next 2 hours...going to get plugs and tester now!!!

Good report! Wouldn't even try to resist! :laugh:
Just install the new plugs (postpone the compression test) and fire it up! :woohoo:

Others here will be far better able to advise with regard to the Keihin CVK34 carbs. (My limited experience is with the Mikuni manual slide designs).

Good Luck!

new plug, no change. Still pouring smoke out 1/2, still no effect if you pull the #2 plug cap.

However, the old spark plug was black and kinda shiny

Ran the compression test.

The engine was cold, but not ice cold - I had started it about 2 hours ago.

All plugs out, W.O.T., here are the compression numbers, thrice tested for accuracy

#1: 168
#2: 165
#3: 167
#4: 162

So compression is definitely good.

however, i put plugs 3 & 4 in and started it up to see if it would run with the 1&2 plugs aganist the head. Started up rough, but fine.

Stopped and put #1 in. Started up fine, sounds like it does normally in the lower end, #2 sparking big and blue against the head.

However, no smoke out the back, so #2 is definitely the smoky offender. But i happened to try something for no good reason.

I put my hand over the open #2 hole as it was running just to feel and I got a hand COATED with oil.

I smelled it to make sure and definitely no gas smell and definitely oily smelling. My hand felt EXACTLY like after you've eaten a tub of movie theatre popcorn with butter...

I'm going to go zip it all up and take #4 out and see if I get the same feel from it.

With these leakdown and compression numbers, where is this oil coming from???!!!???

I had taken the head off this winter and replaced the stem seals so i can't believe it's from above. But if from beneath, how did I get this compression numbres???

Is there any other way for #2 to get oil in it so much?