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Discussion Starter #1
Folks --

Have a 1979 KZ650 which has always backfired under deacceleration (which means unspent fuel in the pipes, I think) and now I've noticed that the #2 cylinder isn't firing on cold start (it usually starts firing after a few minutes of riding if I really crank on the throttle) and then seems to ride ok. Did a pressure test on the #2 cylinder some time ago and it was different than the others (higher, if my memory serves -- it was some time ago). Anybody care to speculate on a cause and/or a treatment? Engine also has a rattle at about 6500 RPM (goes away lower and higher) that seems to be coming from the top half of the engine. I'm not sure if that would be related. My mechanical technique of choice, regardless of the malady (running rough, bald tires, electrical problems, etc.), is to pour a bottle of gas treatment into the gas tank. :) Seriously, I just like to be able to have something intelligent to say to the mechanic when I go in. Thanks. (Just discovered the forum. Looks great!)
Paul
 

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Maybe a sticky float leaking into the cylinder, causing carbon buildup thus causing the higher compression. When cold, the excess gas could cause loss of spark and then once everything warms up the plug burns off and starts working. Have you had the plugs out and looked at them? The rattle may be the cam chain if you haven't adjusted it.
 

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As a footnote, you should only use enough gas treatment to treat your tank's size. A bottle is made to treat a CAR tankful (14-20 gal.) Your bike holds 3 1/2- 4 gal. Too much might help eat a float needle's rubber tip. :roll:
 

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Discussion Starter #4
Thanks, Bob. I'll have to check out the float. Would the carbon, if the other problem is corrected, just burn out eventually, or will I have to perform major surgery? I do the "ratio" thing with the additive, but thanks!

My cam chain is the "non-adjustable" type.

Paul
 

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The carbon (if that is the problem) might burn off if not too heavy. The problem may lie elsewhere as well. Have the valves ever been adjusted? How long ago? What compression reading do you have?
 

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For sale $1000.00 firm. Two 1978 Kawasaki KZ650’s. One in very good condition, recently painted and sealed gas tank. New points, plugs, shocks, brakes and battery. Many extras, crash bars, backrest with rack, shop manual two extra sets of new in the box points and plugs, oil filters. The second KZ650 is a parts bike, this parts bike is taken apart but includes all the parts, it ran when I took it apart for a project that I never got around to. I bought a new Kawasaki and probably won’t ride it anymore. Titles are clear for both bikes.
For more information or to see,
contact Bobby Jones at [email protected] or at 583-2596 leave a message
 

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Hey guys, just found this thread through a google search. I just got a 1979 KZ650SR from my dad and it has the same problem. #2 cylinder won't fire yet it has spark...plug stays wet. It will start to fire after being on the highway and letting her rip!!! A mechanic told me that the vacuum operated fuel petcock sucks and will let fuel run down into the vacuume line which keeps the #2 flooded I believe. However, I rebuilt my petcock yesterday which stopped the #4 carb from peeing every 20 min., but I am still only running on 3 cylinders. Any ideas?
 

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"Have a 1979 KZ650 which has always backfired under deacceleration (which means unspent fuel in the pipes, I think) and now I've noticed that the #2 cylinder isn't firing on cold start (it usually starts firing after a few minutes of riding if I really crank on the throttle) and then seems to ride ok."

--Your symptoms are from a bike running TOO LEAN. Do you notice popping or hot oil smell from your bike when it sits and idles? Generally speaking, air screws get turned 1 1/4 turns out as a starting point.
 
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