Cylinder #2 Cold ('78 kz650)

sft1662 wrote:

Ed - I just put in all new NGK B7ES plugs and it ran beautifully right after I changed them. Which was only about 5mi before the issue happened. I have read that some plugs (esp. NGK) have been recently known to crap out soon after installation, so I'm going to try a new plug if it does it again.

Those plugs should work ok; they're the correct heat range. If you do decide to try a different set of plugs you might want to try ND W22ES-U. I've beed very pleased with their performance on my KZ650.

Regarding the air leak test, you want to set the idle as low as possible and spray the carb cleaner around the joint where the carb holder (on the engine side of the carbs) meets the cylinder head. If there'a a vacuum leak there the engine will die or run differently when sprayed. If this happens, new carb holders should be installed because there will be fine cracks on the mating surface of the old holders. Spraying on the air box side of the carbs won't reveal this leak. Ed

Okay, did the air leak test...notta no change in behavior

Couldnt find a new plug in town so switched 1 & 2 - not the culprit (was really hoping it was just the plug!)... 1 was fine, #2 header was the same...warm but i could leave my hand on it - the others were HOT. Let it idle for a few minutes and it didnt heat up any more than that.

I would have changed plug wires but (and this is probably stupid) they are all different lengths, I dont understand how you switch them. 1&4 start on the #4 side so #4 has a short wire, #1 has a really long one and vise-versa for 2&3. I dont know if they are aftermarket and cut to stupid lengths or if I am just a dumbass when it comes to this sort of thing.

PS, beyond stripped points screws and stripped oil filter bolt, i just found a completely missing bolt on the engine case :blink: one of the top #8's on the clutch adjuster cover thing... and I'm just gonna guess that its not there cuz the PO stripped out the threads on the engine! Getting pretty bummed out as I've only had this bike for a week and am now broke with a broken bike :X

pity party over...

Vter Bob wrote:

Check the sight glass, is your oil level overfilled? Just me, but I'd not ride the bike if you are getting gas in your oil. You are correct, the gas gets blown by the rings from compression. It also dissolves the oil coating your cylinder walls. Running the bike in this condition could lead to scored cylinder walls. An overfilled crankcase can cause oil to blow out the crankcase vent and fill your air box.

Ya...its a tad over the top line... ...good thing my breather hose is shot so its mostly spewing on the back of the engine. :pinch:

sft1662 wrote: "Okay, did the air leak test...notta no change in behavior. Couldnt find a new plug in town so switched 1 & 2 - not the culprit (was really hoping it was just the plug!)... 1 was fine, #2 header was the same...warm but i could leave my hand on it - the others were HOT. Let it idle for a few minutes and it didnt heat up any more than that."

Actually, this isn't really bad news.Sounds like the carb holders are ok and the coil is firing #3 so the coils and ignition systems are probably ok. #2 coil wire or cap could be bad; you may need to dismount the coil to have enough slack to swap #2&#3 wires at the plugs. Assuming the wires and caps are ok, and considering that the bike ran well on all 4 for a short period of time, I'm betting on the #2 carb needing to be cleaned a little better. Before you do that, you may want to check the compression to make sure #2 is ok, but I suspect it is since the bike ran ok for a while. Ed

Would also perform clear tube test on #2 carb to assure fuel level inside float bowl is within specs. And especially to assure that the fuel level isn't too high, which can cause excessive richness in an otherwise perfect carb, and quickly foul the spark plug.

Good Fortune!

Are existing spark plug wires old and hard, and possibly leaking voltage?

Are the spark plug caps equally old, and maybe poorly attached to the wires?

Could run engine in the dark, and look for errant sparks.

Might really put it to the test by using a common household hand-held sprayer to squirt water mist over coils and plug wires while engine is running.

Would also assure clean snug battery terminal connections, including where negative cable attaches to rear of engine.

Has spark quality been visually observed with spark plug removed while spinning over the engine?

Has voltage at ign coil primary terminal been measured, and found equivalent to voltage across battery terminals?

Has voltage been measured across battery terminals at idle rpm (look for for 12~13 vdc) and at 4000 rpm (look for 14+ vdc).

Just some thoughts.

Good Fortune!

Patton wrote:

Are existing spark plug wires old and hard, and possibly leaking voltage?

Are the spark plug caps equally old, and maybe poorly attached to the wires?

Could run engine in the dark, and look for errant sparks.

Might really put it to the test by using a common household hand-held sprayer to squirt water mist over coils and plug wires while engine is running.

Would also assure clean snug battery terminal connections, including where negative cable attaches to rear of engine.

Has spark quality been visually observed with spark plug removed while spinning over the engine?

Has voltage at ign coil primary terminal been measured, and found equivalent to voltage across battery terminals?

Has voltage been measured across battery terminals at idle rpm (look for for 12~13 vdc) and at 4000 rpm (look for 14+ vdc).

Just some thoughts.

Good Fortune!

YEP YEP YEP.

COMPRESSION.
Gas and Air in proper portion.
Correctly timed healthy spark.

Check'em!

Good luck.

Thanks Guys

However I am now more confused... Just tested the plug wire (unplugged it while engine going and the engine almost died, there is definitely juice flowing through the wire, and the plug works because i switched it with #1 which was working fine) The plug caps and wires seem to be in good shape, soft, pliable, etc... and I did the spray bottle test and nothing happened, no visible sparks in the dark either... Does this more or less rule out an electrical issue?

I would love to check compression, but I dont have a tester...when I get paid I'm going to invest in a multimeter and compression tester. Plus I really dont want to find out something bad about the compression...

So I'll visually check the electrical connections tomorrow when its light out (no garage...) and change the gassy oil... then - next stop carb? (I'll do volt/compression tests ASAP)

Do I need to get new gaskets if I'm taking apart the carb, any special tools? I dont know if I'll get to this until the weekend...

Keep up the help guys I appreciate it

Wanted to add something...

I dont understand why if its not burning properly (ice cold header when the others are hot), why did it nearly die when I took the plug cap off? Does it affect the #3 cylinder or something? Does this point to compression... :blush: or does this point nowhere....?

Before further addressing carbs (except fuel level in floatbowl), would check valve clearances to assure they are within specs.

As earlier noted, compression is one of the essential elements for combustion.

Often, weak compression may be remedied by adjusting valve clearances.

A too tight valve (i.e., insufficient clearance) in #2 cylinder could result in low compression and thereby weak or failed combustion even with a perfect #2 carb.

But even where compression test psi figures are within specs, the valve clearances should also be checked. Because too tight valve clearance may allow loss of compression when engine reaches normal operating temperature. The clearance (i.e., "gap") allows for normal metal expansion as the engine temperature rises whereby the valve may continue to seal in its seat.

It is therefore important to know about both compression and the valve clearances.

It's relatively easy to check valve clearances, using a feeler gauge. Whereas the adjusting procedure gets more involved. But sometimes the clearances are found to be perfectly okay, without needing any adjustment.

Good Fortune!

sft1662 wrote:

Wanted to add something...

I dont understand why if its not burning properly (ice cold header when the others are hot), why did it nearly die when I took the plug cap off? Does it affect the #3 cylinder or something? Does this point to compression... :blush: or does this point nowhere....?

Yes, removing #2 spark plug cap "kills" spark on #3 plug.

The so-called "secondary loop" runs through the coil, both plug wires, and both spark plugs. The engine head itself completes the loop between the two spark plugs. The secondary winding inside the coil completes the loop between the two plug wires. The design is for both spark plugs to fire simultaneously.

Removing #2 spark plug from the loop by taking the plug cap off caused the #3 spark plug to quit firing, even though #3's cap remained attached. In other words, removing #2 cap broke the loop.

Good Fortune!

my somewhat educated because it happened to me guess is the choke well on #2 is plugged up. a fine wore and some carb cleaner will remove that issue post haste. post your results...steve