Kawasaki KZ 750 LTD - hesitation and missfire

Well, here is the thing.
The bike has a little hesitation or misfire... I am not sure. But from idle speed and up to 3000 rpm, if I keep the same throttle position (wich by the way is minimal throttle), the RPM go up very slowly, and suddenly, after the 3000 they go up like a beast (still keeping the gas at the same position). This is particularly annoying when I am cruising at low speeds,,,,you can tell/feel there is something wrong with the bike.
However if you open the throttle wide open, the engine goes up perfect...lots of power up to the red line, no matter what gear. Nice :evil:

Things I have checked:

a)with engine off, contact key ON, the voltage at the coils is 11 Volts. Battery is 12Volts. Cleaned contacts, wires, etc....only 0,1 volt gain. So it is a 1 volt drop form the battery to the coils. Is it too much? do you recommend to do the coil relay mod?

b)coils resistance is a solid 2,4ohms in both

c)plug reading is ok for me... a little brown/gray band with a sooty base ring.

d)carbs have been cleaned 6 months ago, I use the bike on every Sunday.

e)no air leaks at carb boots or air ducts to the airbox. (all new from Z1 enterprises)

f) Sometimes, not always, there a little white smoke on the left muffler, and today I feel the 2nd cylinder takes more time to heat the exhaust pipe than the other three. Once the bike is hot, no more smoke.

Any tips? :blink:

Please, see below video to see what I am talking about:

A good battery engine should be just over 12 volts. At idle it should be about 12.3... I think... and at 4,000 RPM should show about 14 V. I think 11 volts at the coils might cause the issue you describe. A lot of knowledgeable people here on the forum recommend dont do the coil/relay mod but you have cleaned all the contacts in the ignition system and still are 1 V low. I have to admit that I did the coil relay mod and went from 11.3 V at coils to 12+ and am happy with the results. Easier starting.

Other things to check would be plugs - new or old ? Clean or dirty ? Good connection between plugs and plug caps ? between plug caps and ignition wires ? and good connections between all wires and the coils. Fine sandpaper and dielectric grease are great.
Check the resistance in the plug caps. Caps dont last forever.

If not already done, would

Assure proper function of timing advancer.
Use timing light to watch the advancer quickly move back and forth as rpm is varied by blipping the throttle.

Lube pivot points on the timing advancer.

Adjust carb pilot screws.

Sync carbs.

Good Fortune!

Do you have a timing light? If so place on each plug wire the inductive pick up lead, one at a time, and see if the spark is consistent on each cylinder. It sounds like it could well be a ignition issue. But also make sure the Vacuum caps are in place on the intake manifolds/ carb holders. Make sure the hoses for the Air switching valve are not leaking, or cap them off. These are the vacuum lines that go into a Tee, then up under the tank to the Air Switching valve. Either to rich from to much fuel, or to lean from to little fuel can cause a miss-fire. Fuel level in the float bowl, lose jets, leaking float valve seat o-ring, etc will make it rich. Vacuum leaks, plugged circuits will make it lean.
You can check the compression, if you have a gauge, with the throttle wide open, making sure all cylinders are serviceable.
You can see which cylinder is colder by splashing a bit of cold water onto the header pipes comparing how quick it sizzles/ evaporates, or using a Infrared Thermometer. This might help you with the miss.

Thanks for all the advices and tips.

I don´t have a timing light, may be it is a good time to finally buy one.
The carbs were done, sync in engine bench and road tested by WiredGeorge...I trust him and his work... I will start digging from the ignition side first.

As far as I know, the timing cover has never been removed and the engine was never open (bolts and nuts have no sign of being used). The bike has electronic ignition (CDI), so no points here. It is a KZ 750 H2.

Spark plugs have only 500 miles, NGK B8ES as recommended in the manual.

Plug caps are NGK japan, but no resistance there. Model NGK LZFH 90º.

Things to check:

a) Cylinder compression
b) Exhaust temp by splashing water (I think I can get borrowed an infrared thermometer)
c) Leaks at emission control and vacuum hoses
d) Fuel level at the float bowls with clear tube test

By the way, if something is wrong with ignition: wouldn´t it be present and molesting in all the range of rpm? :huh:

undiablo wrote: ...carbs were done, sync in engine bench....

Because combustion efficiencies differ among different cylinders on different engines, a perfect bench sync should be followed by an engine-running sync on the particular bike to which the carbs are fitted.

Good Fortune!

They way it was popping, and running on three was what made it seem like it could be an ignition issue.
What's the story behind the bike? Have you had it running before? Owned it long etc?
Since you got rebuilt carb from WG, was it because you had an issue then?
Before you installed the carbs, did you clean your fuel system; Tank/ petcock? Lines/ add a fuel filter/ fresh fuel?
It doesn't take much to plug a Pilot Jet. Or maybe the packaging from shipping them south got a small piece inside the Carb lodging in a Jet? You could pull the Idle Mixture screw from the Carb/ cylinder not running correctly, and blow out the circuit with compressed air.

It sounds like the ignition advancer is frozen in an advanced state.Take off the cover and see if you can twist the advancer to the right easily.It should snap back fast.You should be able to see the fly weights move out and back.Unless it it is moving super free,you might want to take it appart and clean and lube it up anyway,especially if it looks like it has never been maintained.

I have some news.

Today I checked compression, this were the results:

Clean
Cylinder 1: 105 psi
Cylinder 2: 95 psi
Cylinder 3: 100 psi
Cylinder 4: 95 psi

with 5cc of oil
Cylinder 1: 122 psi
Cylinder 2: 110 psi
Cylinder 3: 120 psi
Cylinder 4: 112 psi

Compression was checked with full open throtle and warm engine.

Havakaw: I will check the ignition advancer the next week.I can swear nothing has ever been opened in this bike, so it is worthy to check.

Motorhead: I own the Kz since March 2012 with 10k miles. Now it has 11k miles. I bought it from the 2nd owner in Argentina, but the bike was imported from USA in 1995. Don't know how many owners it ihad back in those days.
When I bought it, it ran like crap. This is the things I've done so far:

Brakes:
a) Repair all 3 caliper
b) Change brake fluid and purge the lines
c) Repair the brake master cylinder

Transmission:
a) Change front and rear sprocket. Do the 630 to 530 conversion. new RK x-ring chain. (NOTE: all the transmission was ORIGINAL from factory, worn out).

Gauges:
a) Repair speedometer
b) New speedometer cable
c) New tachometer cable
d) New pilot cover

Carbs:
a) Buy a new set from WG (Packing was really good, I don't think any dirt could get into them).

The carbs installed in the bike where very dirty and nasty...driving the bike was really annoying.
When I installed WG carbs (a set of Keihin CVK 34), the change was awesome. So awesome :evil: , I did not want to pay attention :whistle: to the missfire between 2k an 3.5k, it was a little detail compare to the past. I have to confess I really don't remember if the problem was present in the past. Now the bike is getting nicer...I want to find the solution.

b) New intake boots
c) New carb holder boots

Engine:
a) New oil filter
b) New air filter
c) New mineral oil CASTROL 20w50 JASO MA

No leaks (test with WD40) in carb holders, intake boots or emission/vacuum hoses.

Ignition:
a) New NGK spark plugs B8ES
b) Check voltage at the coils: 11 volt vs 12 volt battery (1 voltage drop)
c) Check coil resistance: 2.4 ohms in both of them

Fuel system:
a)Clean fuel tank
b)Change fuel line
c)Add an inline VISU fuel filter

Exhaust system:
Nothing really, exhaust is original. But I notice cylinder 2 exhaust pipe takes longer to heat up.... :huh:
Sorry for my possible english mistakes

Things remaining to be done:
a)Check valve clearences
b)Fuel level at the float bowls
c)Check ignition advancer and lube it

What do you all KZ riders think?

undiablo wrote: ...installed WG carbs (a set of Keihin CVK 34)...Things remaining to be done:
a)Check valve clearences
b)Fuel level at the float bowls
c)Check ignition advancer and lube it
What do you all KZ riders think?

Chances are very good that the fuel levels as received from WG are already set perfectly, and would not attempt to adjust the fuel levels unless absolutely positive about exactly how to proceed with both the test and any subsequent adjustment. In other words, I would suggest not casually messing with the float tang adjustments.

Good Fortune!

Today I inspected the mechanical ignition advancer.
It was very rusty, however the 2 arms were not stuck. When I moved them, I could feel the 2 pivots do a squeegee sound...the were dry. So cleaned everything with WD40, applied some oil at the pivots and finally applied some grease to the crankshaft axle.




Changed the gasket also, the original cracked in pieces.

Turn the ignition key on, choke, clutch, start...and boom! The miss-fire or hesitation improved a lot! It is still there, but it is almost 50% less than before :laugh: .

Where should I continue?

i would take apart the advance and lube with white grease.then use timing light to make sure it is in time and advance working right.