KZ650 White Smoke after Heating Up - Both Pipes

Working on this 79 KZ650SR. Just set the valves and cleaned, the carbs, air filter, and replaced the plugs and ignition coils.

Anyhow, when it heats up sitting on center stand, it smokes quite a bit out of both pipes. Also, noticed some white white somke coming out of the air filter intake hole.

Spark plugs are a dry black, not wet or oily. Compression may be a little low, ranges 130-150 per cylinder.

I did not run this bike much before i bought it. It smoked before some, probably the same, so I did some work to it.

I also removed the 10mm drain plugs at the bottom of the exhaust and ran it to see if it would blow out any oil or fuel. Nothing leaked out while running or drained after.

I am leaning more towards a carb fuel micture issue rather than an oil problem.

The wierd thing is it smokes when it gets hot, choke completely off. This is on the center stand, not moving.

Seems to have good power otherwise and runs well. I am not sure if the some from the air box is coming from the carbs or from the air boost hose, not really sure how that system works.

just make sure its full of oil and go and ride it, its not going to blow

Would sniff-test crankcase oil and check its physical condition to assure absence of fuel contamination. If not recently done, would consider changing oil and filter.

Good Luck!

Would also double-check ignition timing at idle rpm and at 4000 rpm (using a strobe-type timing light).

Also assure spark plugs are exactly as factory recommended, and not a "hotter" plug.

And if not already doing, should avoid long term engine running with bike on center stand as the engine heats quickly to above normal operating temperature without the air flow necessary. Best to use a fan to maintain air flow while the bike isn't moving. I use a floor-standing box fan to keep the engine from overheating during maintenance procedures such as timing, carb setting, etc.

It's unclear to me why leaning more towards a carb fuel mixture issue rather than an oil problem... good power otherwise and runs well...., because running well and having good power are not classic signs of a carb fuel mixture problem. The black plug reading imo indicates the overheating likely isn't resulting from a too lean fuel mixture.

Good Luck!

boojr wrote:

Working on this 79 KZ650SR. Just set the valves and cleaned, the carbs, air filter, and replaced the plugs and ignition coils.

Anyhow, when it heats up sitting on center stand, it smokes quite a bit out of both pipes. Also, noticed some white white somke coming out of the air filter intake hole..

The only thing I have seen make white smoke is oil or anti-freeze. You can rule out the second one in this case.

Carb mix problems can make black sooty smoke.

Oil may be contanminated, have not changed as of yet, may have some fuel dilution.

I would have to say the reason I am leaning toward a carb problem is due to the smell of the exhaust and my KZ400 acts the same way on the left side after sitting for a while.

Also, both pipes are doing it, not just 1 side. It's not the blue white and smell of oil smoke and is not black such as unburn fuel.

Maybe part of the issue may be the air boost system. Not sure how that works, but am getting smoke from the air box. - Also that kind of led me to the carb problem.

Did a compression test with the engine cold - I know that does not mean much, but values were 120-150 with throttle fully open. Does compression typically increase as the engine warms up?

boojr wrote:

Oil may be contanminated, have not changed as of yet, may have some fuel dilution... am getting smoke from the air box. - Also that kind of led me to the carb problem....

Excessive blow-by due to oil contamination (from fuel getting into crankcase) is consistent with getting smoke from the air box (where hose connects crankcase vent to air box).

Usually, fuel intrusion into the crankcase does indeed begin with a carb problem (such as leaking float needle accompanied by blocked overflow circuit). But am doubtful that smoke from the airbox is coming directly from the carbs. Because air from the airbox flows to the carbs and not from the carbs.

Good Luck!