TOPIC:

Hi everybody, new member here. I have had my KZ650B for about a month now, I should have some pictures up in the members section later this week. I have been spending a lot of time on this site and thought you guys might be able to help me trouble shoot this problem I am having.

Everything was running great (smooth idle, no vibrations, clear exhaust)until Saturday at which point the following happened.

I am driving along smoothly in 5th gear when I pull in the clutch to gear down, before I let the clutch out again I notice the tach is at zero. I eventually pull over and visually inspect the bike, nothing. So I start it up, it backfires on me and definitely isn't idling as smoothly so I drive it back home (30km's).
When I get to my place I notice an oil/gas stain around one of the spark plugs. I check the exhaust pipes and notice that the pipe coming out of the cylinder with the leaky spark plug is not very hot, so I figure its safe to assume its not firing. The exhaust at this point is fine though, no smoke.

Yesterday I take the spark plug out and it is extrememly dirty so I put in a new one. The bike starts immediately and all 4 exhaust pipes heat up immediately; all cylinders firing. After about 30 seconds the exhaust turns pretty smoky. I shut the bike off, unplug the spark plug of the problem cylinder and start it up again. Obviously doesn't run quite as smoothly this time but there is no smoke at all this time.

So I am thinking its the O-ring for that piston that is causing all this, or possibly the head gasket. What do you guys think, am I way off here?
BTW, I am completely new to bikes so forgive me if I have made a some newbie mistakes here.

Thanks
Zen

Zen:

I have never heard of an "o" ring on an internal combustion engine piston therefore I assume you are refering to the compression and/or oil rings.

(1) I would suggest that you obtain a good service manual and become familiar with your machine.

(2) Do a complete compresstion check of all cylinders.

(3) Do a leakdown test of all cylinders. This will tell if there is leakage past the rings.

(4) If there is no leakage past rings you most likelyu have a bad valve stem seal.
Harry

Harry, I think when he says "oring" he is talking about the aluminum crush washer that is press-fit onto every spark plug...

Zen, that theory is easy to check by using another spark plug. Put some anti-sieze compound on the thread and snug it... don't overtighten but snug enough so the "oring" starts to compress and see if that fixes the problem.

Harry brought up some good tips. Get a service manual. Then do a compression test. When the bike TOTALLY dropped running, that doesn't suggest a compression problem but sounds more like electrical unless the bike just quit running. Next, it does sound like one of your cylinders isn't firing. The bike WILL run on three cylinders. An easy check is to find a spray water bottle and spray the pipes. Cylinders not firing will allow the water to roll off where firing cylinders will vaporize the water.

Once you have determined which cylinders are not firing, proceed trouble shooting from there.

Non-firing can be a wide variety of issues. I would first start by performing a tune up in the order suggested by the service manual Harry has suggested. I would look especially at electrical issues like plugs, points, condensors, plug wires/caps, and how the wires seated in the coils. I would adjust the timing using a timing light. Before doing that, adjust valves and check compression just to benchmark the health of the engine.

Once you are sure you have good spark and good compression, it is time to move to the carburetors... kinked hoses, dirt, dirty fuel filter, could be a lot of things that might cause the problems you have observed. Do the carbs last.

Thanks guys, I will be doing a compression test this evening and I am awaiting the service manual in the mail now. I don't know why I said O-rings; you are right Harry, I meant the oil rings.

I'll let you guys know how it turns out

Zen

Thanks George:
It would appear that I completely misread the posting.

Ha!!
You just wait until you are past eighty and see how acurately you read.
Harry

Welcome as well O. Lets have some pix of that 650!

Hope you solve your problem.