Cylinder #2 Cold ('78 kz650)

Hi all, time to bother you with another question (small novel, sorry) - I searched and found some info, but my situation seemed a little different from the other dead cylinder topics.

So I recently adjusted the points gap (stock ignition), new plugs ,oil, filter, air filter, and the bike ('78 kz650) was running better than ever until yesterday. The carbs were also cleaned, rebuilt, and synched about a year ago. I started it up - via kickstarter as usual because my battery gets drained before it starts up after sitting in the cold for a couple of days - and it sounded throatier than usual. At the time I thought "sweet, my bike sounds meaner today", I've only had it for a week so I'm not fully in-tune to little changes in how she runs. It was taking forever to warm up so I could take it off of choke, even longer than usual, and after 5mins I took the choke off and tried to apply power and it would bog down.

Fast forward 5mins, I realized that the #2 header was cold. Pulled the plug and it was not really wet, which was wierd? Put the plug back in and tried to ride it a bit in hopes that the problem would cure itself, and after the bike almost dying a few times (and sounding like a tortured bullfrog), I got it going and rode around the block. Felt the pipe after this and it was hot - things were firing. I then went on a 30 mile ride and things were fine, and it fired up super fast after using the electric starter when it was still warm.

My instincts make me believe this is probably an electrical issue (just weird that the plug wasnt that wet), maybe just need a new battery. If it happens again I'm going to put a different plug in, new battery, and go from there. Any thoughts?

I am currently also working on a 79 kz650. This one had a cold pipe on #4. After cleaning the carbs a couple times I found that the plug was not wet. So while the bike was running I sprayed some carb cleaner into the back of the carb for #4 . She started to pop and wanted to take off. Come to find out I also sprayed around the intake boot. That was the problem ,it was sucking air around where the boot meets the head. So I am replacing the boot. Might try this on yours .

The only time that ever happened to me, the vaccume line had a hole in it and it was sucking a ton of air. Replaced the line and it solved the problem.

A new battery is well worth the money.

dshelly wrote:

I am currently also working on a 79 kz650. This one had a cold pipe on #4. After cleaning the carbs a couple times I found that the plug was not wet. So while the bike was running I sprayed some carb cleaner into the back of the carb for #4 . She started to pop and wanted to take off. Come to find out I also sprayed around the intake boot. That was the problem ,it was sucking air around where the boot meets the head. So I am replacing the boot. Might try this on yours .

So you basically just spray carb cleaner at the intake boot and if there's a hole it should start popping? Makes sense!
I didnt think of it being a carb/air issue but it makes sense because of the dry plug. Would it make sense for it to start running good after a while if thats the problem? Thats the only reason I was thinking electrical (that and the plug could have been a little wet... I should have been paying closer attention but was kind-of in a "WTF IS GIONG ON!?" type of mood), but either way its definitely worth the quick test. Thanks guys

I figure the new battery needs to happen either way, that way I can find out if its just my battery that is causing my crummy electrical output or if i need to go more in-depth into my electrical system...

If it's just #2 that's cold I would suspect a bad plug, plug wire or plug cap. Cylinders 2 & 3 fire off the same coil. Try swapping the wires on on 2 and 3. If the problem follows the wire, well there you go. If not I would suspect a fuel blockage (You did say the plug wasn't very wet) or an air leak like already suggested. Do you have an inline fuel filter on the bike?

What spark plugs are you running? Ed

Bob - The bike has an in-line fuel filter, and since the carbs were recently cleaned (200-300mi ago) I think that if its a carb issue its probably due to an air leak and not a clog. Could be wrong cuz I'm new at this, but thats my hunch anyway

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.

So my tests will be: plug, carb air leak test, battery. Just got home from work so I'm gonna go fire her up soon and see what happens. I'll take better care to see if the plug is wet if it fails again... would it be pretty noticeably wet? (probably a dumb question) I've only seen wet-fouled spark plugs on 2 stroke bikes and the oil makes it pretty obvious :dry:

Thanks again for the help

There's a number of members on here, me included that have assumed because the carbs were just cleaned, they can't be the problem. Safe to say a good percentage of us were proven wrong. Another suggestion I have for you if you've ridden the bike any distance without number 2 firing is to unscrew your oil filler cap and take a sniff. If you smell gas I'd add an oil & filter change to your list of things to do. I have experienced NGK plugs being bad right out of the box and also going bad after a few hundred miles. They have never gotten better by themselves however. Just trying to help...

Okay, update... #2 still cold

She fired right up with 3/4 choke and the electric starter, but #2 was cold. The battery still had enough charge from my 30mi ride yesterday and it got up to 50 degrees today so I'm sure that helped, but this combined with the fact that its just #2 and not #2+#3 has convinced me the weak battery is a separate issue.

Once i took the choke off it sputtered and bogged down like normal but I was able to rev it up a bit and noticed that #2 pipe started getting hot... so, I dont know... I checked to make sure the choke was engaging on all cylinders and it was. I pulled the plug to make sure it was sparking okay and it was, and it wasn't really wet but by the time I pulled it the #2 pipe was hot so it had been firing for a bit. It could still be a faulty plug that is only firing some of the time right? The carb seal on the airbox looks good, but I'm gonna go pick up some carb cleaner and spray it and make sure... Once I rule out the air leak I'll try a new plug, but I have a feeling cylinder 2 is only going to act up when its cold. Keep the suggestions/thoughts rolling!

Vter Bob wrote:

There's a number of members on here, me included that have assumed because the carbs were just cleaned, they can't be the problem. Safe to say a good percentage of us were proven wrong. Another suggestion I have for you if you've ridden the bike any distance without number 2 firing is to unscrew your oil filler cap and take a sniff. If you smell gas I'd add an oil & filter change to your list of things to do. I have experienced NGK plugs being bad right out of the box and also going bad after a few hundred miles. They have never gotten better by themselves however. Just trying to help...

Thanks Bob - I know that the carb is not completely ruled out, but with my tiny budget (just bought the bike & in school) and limited time/toolkit I'm working from easiest on up I very well may have ridden without #2 without even knowing it, so I'll go smell me some oil, good call!

---YEP...oil smells gassy... how does that happen? just drains down through the cylinder walls? Should I change it before I ride at all? If it wont do too much harm I'd like to solve this issue before I change the oil so that I'm not changing it every other day...

At the risk of sounding like a smart ass (not my intention at all) It's an easy thing to try, next time you start the bike and the problem occurs, turn it off, swap 2 & 3 plug wires. Fire the bike back up. If the problem moved, it's an electrical issue (wire, plug or cap). If it doesn't move, you have a fuel/air problem. BTW, was a compression test done?

I truly understand the constraints of a limited budget. Been there done that (more than once) I had a bad plug cap that was intermittent and it drove me nuts for nearly 2 weeks.

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.