Trouble with my 750, I miss my 440

Hi everyone,

I had an 81 KZ440 for a couple years and recently sold it to upgrade to an 84 750. It is complete and has 13,000 miles and is in pretty decent shape although it is obvious that it spent sometime outside uncovered. Now here is where the fun begins. When I picked up the bike it barely ran and the plugs were black. I have recently gone through everything that I can think of; I cleaned the carbs and replaced all the o-rings, I also balanced the carbs (a lot more difficult to do with 4 cylinders than with 2), changed the plugs and cleaned the timing advance mechanism. I have to say it does run about 10 times better, but there is still something wrong with it.

When cold it starts right up and idles fine. As it warms up though it starts to run really rich, (all the plugs are still black) blowing black smoke out of the exhaust and sometimes back firing when you rev it. What scares me the most though is that if you rev it above 4 grand it will stick there (I checked the carbs and the butterflies close all the way). It’s like having cruise control at 30mph in third gear. After riding it when ever I come to a stop sign it wants to die and I have to keep revving it.

I am not sure where else to look, I have never done much engine work and am hesitant to take more things apart on it than my mechanical abilities will allow. I guess my question is that the cam chain does seem to make a lot of noise, In the book it says that it is self adjusting, could it be a possibility that the adjuster is bad and causing my problems?

Thanks to anyone who might be able to help.

try checking your valve clearences

you are not controlling the fuel
you may need new fuel mixture screw "O" rings

check the float bowl fuel level (float height)
after fixing these 2 details re balance the carbs
this is a carburetor issue.

cam chain fault cause other symptoms

My first suspicion would be that valve clearances are less than they should be... the valves hanging open can cause poor compression and thus, poor combustion accounting for the soot. Do a tune up on the bike per your service manual or Clymers before getting concerned.

As far as the cam chain noise; some noise is expected. I suggest you find another KZRider member in your area and compare your engine noise to that member's bike. You will probably find that these bikes are noiser than you expected.

Last, to the issue of the idle not returning. This can be caused by a number of things but if it hangs as you describe, I would first check the throttle cable. Many new owners like to get the cable tight. You MUST see visible slack in the cable where it connects to the carb assembly. To adjust your cable, go up by the switchgear. Loosen the locknut on the cable and turn the barrel adjuster towards you as you sit on the bike. You might want to look at the cable down at the carbs so that you can OBSERVE some slack on the cable. If that doesn't fix the problem, then there is an AIR LEAK that is causing a lean condition in the pilot system. The most common air leak issues are:

1. Mikuni carbs: orings on mixture screws - Keihin carbs: missing or damaged oring UNDER the little washer under the mixture screw (Keihins don't have an oring ON the mixture screw itself... it is under it)

2. air leaking in vacuum ports... usually cracked vacuum caps or cracked vacuum hoses or just missing caps. There are vacuum ports on the engine side/top of each carb. These MUST be capped securely or connected to the petcock securely by a hose with NO LEAKS or be connected to the emissions equipement with hoses that don't leak. If there is a leak, the idle will behave as you note.

3. intake manifolds not sealing or cracked... even a low mileage bike needs to have new intake manifolds because although they may not be visibly cracked, the rubber tends to harden and not seal well with age. You can spray the area around the intake manifolds with WD40 while the bike is running and if the bike dies or spews white smoke, the manifolds leak. REPLACE (never repair).

When I rebuilt the carbs I changed the o-rings on the bottom of the air mixture screws. As for the vacuum ports I plugged every one with a cap and ran the bike on prime and the same trouble was seen. I did spray the carb boots and did not see any white smoke, (but I will try that again with the tank off so I can get more area) and the throttle is set with a lot of slack.

I guess I will get adventurous and take the valve cover off to check the valve clearances.

Thanks for your help.