Engine running rich...what's the problem?

For the year I've had my KZ750H3. the engine has seemed to be running richer and richer. Now, it still runs strong and starts fine, but it smokes out both tail pipes. This is rich smoke-not oil smoke. It's not strong and can't be seen well when going down the road, but when tuning in my garage it gets pretty bad in there.

What's the first thing to check (the choke works fine by the way)? Thanks!

1st do a compression test if that checks out it may be valve stem seals or valve stem guides or a combination of all 3.If compression test looks good more than likely the head needs attention.if the compression comes up after a few cranks it points to rings.good luck (how many miles any mods?)

Like I said, this is not oil smoke, but black smoke (black whispy is rich-oil smoke is usually blue and lasts, steam is white) from running rich. I see it as a carb(s) problem, not an oil burning problem. There is no oily smell with it. It also gets somewhat worse when I choke it, and the engine seems to be running a bit hotter lately.

The most common smoking problem with these old bikes is HEAD if you feel you must play with the carbs ?are they clean?
Jets? Floats? Filters?Ignition Components? I dont know enough about your bike to make a educated guess yet pics?Ill help any way I can

With the minimal info you gave here's where I'd start...

First: Compression (as suggested). Verify it, it'll be worth your time, trust me.

Second: Valve clearances. If they're not in spec they can (and will) mimic carb issues that you'll NEVER be able to rectify cause there's nothing wrong with the carbs.

Third: Verify timing is dead spot on. Need to do this with a strobe, static timing only gets you so close. If you have factory electronic ignition skip this.

Fourth: Dig into carbs if issues persist.

I was pig headed and resistant the first time someone told me my "carb issue" was actually valve clearances too, but they were right, I was wrong. Definitely worth pulling the valve cover off and checking valve specs before you disregard the years of experience being offered here...

Do all of the regular maintenence required for these bikes as per the manual, valve lash being #1 as mentioned.

Remove your air filter(s) and take a brief ride. If the performance increases considerably, then your are in fact running rich.

Let us know, then we can troubleshoot from there.

Good luck.

what type of carbs are you using also what kind of air filter if its running different than normal i'd suspect possible crap in the float valves or a bad float those conditions will cause it to run rich. especally if it just started doing this. if your float height is to high it will cause the same symptoms have you made any changes to the carbs lately. if so that would be a good place to start.

Clear tube test --
As too high fuel level could cause the reported problem, and because it's so quick and easy to check, would first perform the clear tube test test to determine service fuel level inside float bowls.

Charge battery --
A weak spark could also cause the reported problem. So would also charge the battery and assure good clean terminal connections at battery and where negative terminal cable attaches to engine ground, and that the battery is good and properly serviced with correct fluid levels. All to help assure full voltage to coils, and hopefully a healthy properly timed spark.

Could remove plugs and visually observe spark quality while cranking the engine over.
Look for fat blue spark.

And assure correct valve clearances -- Amen to that.

Good Luck!

How does one do the clear tube test?

polkat wrote:

How does one do the clear tube test?

Takes longer to explain the test than to perform it. :laugh:

Clear plastic tube test

Check real-world float bowl service fuel level.
Quick and easy -- no disassembly required.

May perform test with carbs on or off bike.

Carbs must remain still and level during the test.

Turn petcock off.

Fuel line remains attached to carb.

Remove side-located drain-screw from float bowl.

Use short length of clear plastic tube.
Size of clear tube should match drain-screw hole.
Twist-thread clear plastic tube into drain-screw hole.
Rumor has it some folks prefer using a small plastic barb-style connector fitted into the drain-screw hole with the clear tube attached to the connector.

There's also a special tool available (see below).

Hold clear tube against top edge of float bowl.
Keep it steady - don't let it move.
Turn petcock on.
Watch level fill and rise up in clear tube as fuel fills float bowl.
Fuel level visible in tube matches fuel level inside float bowl.
Slight fuel leakage from the drain-screw hole is immaterial.
Repeat test to double-check result.

Smoothbore carb has larger bottom-located drain-screw hole.
I use a tapered rubber grommet pressed or twist-threaded inside the drain-screw hole with the clear plastic tube fitted snugly inside the grommet.

If desired, a "special" tool is available for fitment to side-located drain-screw holes.
It is a thumb-screw affair with clear tube attached that threads into the drain-screw hole.
Z1e has the professional "factory-style" version. Special Tool

There's another neat repro version on ebay for less that $10 (somebody here will have the link).

With CV style carbs having combined function bottom-located nipple for both over-flow and drain, just attach the clear plastic tube to the bottom located nipple.
This does not apply to carbs having separate independent drain-screws and overflow nipples. Use the drain screw; not the overflow nipple.

Refer to manual for specs as to ideal height of service fuel level.
Usually, the correct level is slightly below the float bowl gasket, say 1/8 inch or 2-4 mm.

Checking fuel level is quick and easy (with carbs on or off the bike).
But adjusting the float to attain the correct level is more difficult.
Don't rely on the upside-down work-bench physical measuring method where results are only ball-park at best (unless you're feeling really lucky).

Adjustment -- carbs removed from motorcycle.
There is a tab or tang on the float whereby the height may be adjusted by delicately and ever-so-slightly bending the tab, noting that seemingly minute adjustments often result in significant changes in fuel level. Usually, bending up lowers the level (closes the float-needle/seat interface sooner), and bending down raises the level (at least for Z1, KZ900 and KZ1000 through 1979). Uncertain about universal application of bending directions, so would inspect working mechanism of the interacting parts to confirm this for your particular carb.

Helpful tip (courtesy of wiredgeorge)-- when re-testing after adjustment, only one screw is needed to hold the float bowl onto the carb, which speeds removal and replacement for testing between adjustments.


Bottom line-- Given good compression and spark, with carbs in as-new condition, synced and pilot adjustments set to specs, no air leaks, and clean air filter. Where new plug quickly soots and fouls from apparent over-rich mixture, a too-high float level is a likely suspect.

Good Luck!

For more info, could do a search on "clear tube test" or "clear plastic tube test" or "fuel level" or similar such key words.

Good Luck!

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