TOPIC:

Hello. I have a 1980 KZ 750 H LTD. The bike is running 4 into 1 exhaust. Pod filters. I am not sure about jet sizes. My bike has been running great the last three years. Toward the end of last season, the bike started to run rough. It would be perfect, then suddenly run real bad, maybe on 2 cylinders. It would be crap for a mile or so, then just suddenly jump back into running great. Then bad again. Then it stopped for about two weeks. Now, the bike idles, but won’t run when the clutch is released. Checked coils for power, both have power. The 1 and 2 plugs show spark. The plugs are really black, after running a few minutes, the plugs looked wet. As you sit on bike the two left cylinders (1& 2?) Exhaust headers are cool after running a few minutes. 3 & 4 are hot.. This seems strange, as I expected trouble to be 1 & 4 or 2 & 3. Any ideas?

Post edited by: bcteel, at: 2007/03/14 19:24

got fire coming from coils? if you do id say start with new plugs;)

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buy a new set of plugs!
wont be a waist of money as spares are good to have around.
plugs get heavily carbon build up and cant conduct a spark properly.
or the spark plugs have just broken down, i have bought new plugs in the past that didn't work out of the box or broke down days later it happens dude.

Old plug wires may be deteriorated and leaking.
A quick fun check is with engine running in complete darkness, spray water mist over plug wires, and maybe get a free fireworks show.

Thank you all for the help so far. Here is where I am now. Plugs are brand new NGK B8Es. Wires are only one year old and are Accel 8.8mm. Now, it seems like when I took out 1 and 2 and lay them on the engine and crank it, I can see spark. But, the 1 and 2 header are still not heating. Also, I tried checking ohm impedence on ignitor and pickup coil. I may have did it wrong, as I got zero reading on everthing. If it was really zero, it wouldn't spark at all, right? Do you think this means a carb problem? Should I make a new post in the carb section?

You probably don't have electrical problems... put away the meter for now and check your valve clearances. I suspect you haven't adjusted your valves in modern memory. Am I wrong? Bike ran good and then slowly deteriorated... problem on two adjacent cylinders... black plugs... new wires/plugs... hmmm

Takes spark, gas AND compression to get good combustion. You ain't got good combustion. All of a sudden too much gas is flooding the two left cylinders? You got spark by your own admission (your resistance measurements were NOT done right or you wouldn't get spark) so what does that leave?

COMPRESSION... OK, maybe your rings suddenly quit sealing but slowly degrading performance? Hmmmm valve adjustment. See the valve adjust tech tip on our web site under "wg's Tech Stuff Index".

WG said: I suspect you haven't adjusted your valves in modern memory. Am I wrong?


I must admit I have never adjusted the valves in the three years I owned it.... I'll check that out.

okay. I was finally able to check valve clearances. Although some are closer than others, all are within spec. Anything else?

Did you do a compression check on the cylinders?

bcteel wrote:

okay. I was finally able to check valve clearances. Although some are closer than others, all are within spec. Anything else?

You say you are getting spark, are you positive you are getting fuel? The reason I ask is because this sounds exactly like what I'm going through right now. I just tore down my carbs and "cleaned" them, but when I put them back on 1&2 aren't firing. They'll fire if I get on the throttle, but at idle, nothing. I know there is spark in the chamber because I put in the colortune to see if my mixture was way off or something. I've come to the conclusion that my pilot jet needs to be cleaned better on those 2 carbs. Might be the same for you.

(WARNING: I have VERY little experience, this is happening to me on a Yamaha XJ650, and I haven't fixed my problem yet. I'm just throwing it out there as a possibility)