77 KZ 750 B

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.

"Soon" is not an adjective that can be applied to a part made over 30 years ago. Coils go bad over time. A coil is actually a high-voltage flyback transformer and they operate under a lot of voltage stress on the windings.


I agree to flushing fuel tank, clean carbs and install fuel filters. Check the carb diaphragms for pin holes or slits they will drive you crazy and make it run crappy.

So we've established its most likely the coil.

To answer your question, to change the jetting you can do a few different things. First you can mess with the pilot air/fuel screw. But to be honest if its stock just set it to factory specs and the perfect setting will be, at max, a half turn from that. If its any more then 3/4 to 1 turn off I'd suggest new pilot jets. Next in the throttle range is the jet needle. These needles have slots on them with an "E" ring attached. you can move the ring up or down for richer or leaner between 1/4 throttle to 3/4 throttle. As the needle sits in the carb, moving the "E" ring up will lean it and down will richen it. Finally the main jet. This has to be replaced with a different sized one. If you have the old style carbs (where the jet is screwed into the float bowl) good luck finding new ones. All I can find are the stock ones. Anybody have a source??

Once again this is much more likely an ignition problem. I had the same problem with mine so I replaced the points, condensor, coil, spark plug wires, and caps on mine right away when I got it. It helped quite a bit. then I tried the coil mod (just to see if it would make a difference no one get upset here) and it really made a big difference. I then removed it and wired it properly. Now it works great and I've had cocoa brown plugs ever since. No jetting needed.

Should be able to have the coil tested at a Kawasaki dealership that has in its shop a coil testing tool known as a three-point tester (or electrotester).

The tool measures whether or not a coil will produce at least a 7mm (.28") spark.

One issue with a coil having permanently built-in high-tension (spark plug) wires, is that the wires themselves get old, hard and cracked, and start leaking voltage, even though the coil itself may remain perfectly good.

So here ya sit with a good coil, but crappy wires causing poor spark at the plug tips.
And it seems difficult or impossible to simply install new wires.

However, a plug wire "splicer" might be a feasible solution.

Available at Z1E, the splicer may be used to connect a new wire.
The old wire is cut from the coil, leaving a stub long enough to attach the splicer between it and the new wire.

Click here > www.z1enterprises.com/detail.aspx?ID=1890

Good Fortune!

I did put a carb repair kit in both carbs and install in-line filters but hasn't seemed to make a difference. I've read discussion about synchronizing the carbs. Could that be the problem? How is that done. I attached a timing light to both spark plugs and could'nt notice any delay or skipping. What is the "coil mod" ?...thank you guys for helping....

bgulsvig wrote:

...What is the "coil mod" ?...thank you guys for helping....

Coil mod is an attempt to finesse faulty wiring and connectors which might be causing loss of current delivery to the coils.

The procedure at this point should not be whether to install the coil mod.

Rather, the procedure at this point should be to compare (a) voltage being received by the coils to (b) voltage measured across the battery terminals.
Measuring voltage at the coil is done with the ignition switch ON.
Ideally, battery voltage (engine off) should be 12~13 volts, and measured voltage at the coil should be the same as battery voltage.
If very close to equal, there's no loss in the existing wiring or connectors, and therefore nothing to supposedly improve with a coil mod.

You earlier asked, How do I check if the coil is at fault, and were advised to 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.

1. What is the observed spark quality?

2. What is voltage measured across the battery terminals?

3. What is voltage measured at the coil with the ignition switch ON?

This info is imo critical to competent diagnosis.

Good Fortune!

bgulsvig wrote:

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 choke turned fully OFF?

Is the air filter fresh and clean, and not obstructed by anything underneath the seat, such as a shop rag, gloves, etc.?

Good Fortune!

Patton thanks for your help. You mention the choke. The weird thing is that it will not start or even fire with the choke "on". It has to be fully "off" and it starts every time but idles rough. What about the carb synching? I've read that it involves vaccum guages but there are no vaccum lines on the carbs.

We are talking about a 750 B twin I assume?

If so my advice to you is this... DON'T SPEND 2 CENTS ON POINTS PARTS. If you're going to spend money on the old girl, make it worth your while.

Hit a scrapper, or parts bike, or new from Z1 Enterprises if they have it and you can afford it, and get the transistor box, pickup, advancer, and coil off a 440 or newer 750.. like the 80,82,83.. take the existing coil, points plate, and advancer, and toss that all in a garbage pile where it belongs.

The wiring for the newer system is very simplistic and you can just use the existing power supply of your harness that was for the old coil. I guarantee 90% of your existing and future headaches will go away FOREVER.

---

Balancing is easy. It's as simple as adjusting you're pilot screws Patton pointed out, until you hit close as possible to the factory vacuum pressure, then adjust the balance with the balancer screw if necessary. (I'll post you a pic of that, I can't spot it in his diagram though I'm sure it's there. DOH!)

With gauges the normal reading is 17 - 23 cm Hg, with a difference of 2 cm Hg or less between both carbs, if it's more than that, just adjust the balancer screw until it is in the proper range. BTW the vacuum gauges go onto the nipples at the bottom of the intake boots on the older models. Should be a balancer hose on there, just take it off and attach your gauges.

If you don't have vacuum gauges you can do it the old backyard style. Set the pilot screws at the stock 1 1/2 turns out from lightly seated to start with. Start the bike and set your idle screw until the idle is a little higher than normal (like 1500 rpm) so it doesn't stall out on you while you adjust the pilot screws.

Place your hands near (not on) each muffler and feel the heat. You want the exhaust from each cylinder to be just warm, not cold, and not hot. Adjust the pilot screws until you're getting the same warm heat from each cylinder. If you can achieve that you're very close to the stock setting.

If you notice one cylinder seems to have more pressure coming out than the other, then do the balance adjustment and balance them out to even pressure. If they feel EVEN already you're good. (I've found that a few minutes doing the bench balancing setting properly usually null and voids the need for the on machine balancing.) Bring your idle back down to normal and you should be good to go.

Also if someone has put one of those K&N air filters in there be sure to first clean it, and then oil it properly. They can really effect the vacuum if allowed to dry out. Bike will idle fine but bog/breakup at mid or high throttle ranges.

Wishing you luck! Glad to see another twin getting revived.

Another piece of advice I have is this:
If in the future you ever get the chance to come across the newer (BS34 carbs and intake boots) off a newer 750, grab em quick and toss those pain in the arse BS38s in the same garbage pile as the old points parts. That will cover the other 9% of your headaches. The other 1% can't be helped as these old girls are well OLD.. chuckle

bgulsvig wrote:

...will not start or even fire with the choke "on". It has to be fully "off" and it starts every time but idles rough. What about the carb syncing? I've read that it involves vacuum gauges but there are no vacuum lines on the carbs.

With only 6000 miles on the bike, it seems unlikely that the carbs have fallen out of sync, but it's of course possible, or maybe the sync has been messed with.
In any event, being out of sync could indeed result in a rough idle, even if the carbs -- and everything else -- are otherwise perfect.

Regarding the choke issue, sounds like the carb pilot circuits might be dirty. More specifically, that the pilot circuit air passages are partially blocked.

It's possible that the choke mechanism isn't allowing full closure. And could oil the moving parts to see if that helps.

Also, could remove air filter as a test running experiment to see whether it makes any difference.

Another possible reason for undue richness is too high fuel levels in the float bowls. May be checked using the clear tube test. Again, due to the low mileage (only 6000 miles), it seems unlikely that the float adjustments would have gotten out of whack on their own. But maybe they have been messed with.

Anyhow, I would first concentrate on getting a good spark before further addressing the carbs. Because even perfect carbs can't compensate for an insufficient or improperly timed spark.

Good Fortune!

I tried adjusting the pilot screws but that seemed to have little affect on things. I did notice a difference in pressure coming from the mufflers. You mention the balance adjuster screw but I can't reach it while the bike is running.......

bgulsvig wrote:

I tried adjusting the pilot screws but that seemed to have little affect on things....

Often indicates clogged pilot circuit when pilot screw adjustment doesn't affect rpm.

Good Fortune!

I have had the carbs off and cleaned/air pressured them many times. How could the pilot curcuit be plugged.
I tried observing the spark last night looking for the "fat blue spark" but I couldn't tell as it was arching in two or three spots on the electrode.........