77 KZ 750 B

My KZ starts and idles fine but when I get going down the road it hesitates and cuts out badly. The spark plugs have black soot which I have been told means to rich. How do I adjust the carbs to make it run leaner?

Is the bike stock, airbox/filter, pipe etc. these will effect the correct jetting.
Also, put in new plugs, and see if they become black and sooty quickly.

Bike is stock with only 6000 miles. I did replace the spark plugs but can not drive it long enough to monitor them... it idles smoothly but runs very rough when I put it in gear and go. It has dual carbs. Where are the rich/lean adjustment screws located?....

New points, condenser, new plug caps, plugs, and check the resistance and voltage at the coil.

My 79 KZ750B was sooting the plugs and fouling them. I screwed with jets and needles for a few months before replacing the coil and learning the coil was the problem. Weak spark will do that. Z1 sells a four Ohm EMGO replacement coil for $36. After wasting that chink of my life, I am a firm believer that old coils should go straight to the garbage if you have any kind of plug problem.

You fellows are talking about replacing ignition parts like points condenser and coil. The bike has 6000 miles. How can these parts go bad so soon. How do I check if the coil is at fault. The spark plug wires are attached to it (all one unit).

bgulsvig wrote:

You fellows are talking about replacing ignition parts like points condenser and coil. The bike has 6000 miles. How can these parts go bad so soon. How do I check if the coil is at fault. The spark plug wires are attached to it (all one unit).

How do I check if the coil is at fault ---

Would visually observe spark quality at plug tips with bases held against engine head while spinning over engine.
Look for fat blue spark. Best to test using brand new plugs matching factory specs.

Poor quality spark, such as weak orange, may result from other issues besides a weak coil. In other words, may have a weak spark on plug tips even with perfect coils.

Great spark requires sufficient voltage being received to perfect coils, AND proper signals to the coils (via correct timing, wiring, etc.), AND a perfect secondary loop (plug wires, caps, and plugs, with perfect connections @ coil>plugwire>cap>plug).

Good Fortune!

bgulsvig wrote:

Bike is stock with only 6000 miles. I did replace the spark plugs but can not drive it long enough to monitor them... it idles smoothly but runs very rough when I put it in gear and go. It has dual carbs. Where are the rich/lean adjustment screws located?....

Part No. 33 (see third post below) is described as pilot air screw (not as pilot mixture screw).

If truly a pilot AIR screw, it turns out to get leaner pilot circuit by adding more air.

If actually a pilot MIXTURE screw, it turns in to get leaner pilot circuit by reducing amount of mixture.

Would confirm which way turning actually leans the pilot circuit, and then experiment with test running a leaner pilot circuit (say 1/2 turn on each carb pilot screw --- turning whichever way actually leans the pilot circuit) to see if leaner pilot circuit reduces plug sooting.

Good Fortune!

bgulsvig wrote:

You fellows are talking about replacing ignition parts like points condenser and coil. The bike has 6000 miles. How can these parts go bad so soon. How do I check if the coil is at fault. The spark plug wires are attached to it (all one unit).

Every part on that bike is 33 years old.It aint the mileage sometimes as much as it is the age.Things go bad with age even if they have 0 miles.bj

Carb pilot circuits may need cleaning, regardless of low mileage.

If not already fitted, should install a good aftermarket in-line fuel filter.

Click here > In-line fuel filters at Z1E

Good Fortune!

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