Oil Leak 73 Z1 900

Good guesses, thanks everybody!
No, the chain oiler is up on a shelf, and hasnt been on the bike in a while.
The oil is definitley coming up through the crankcase breather and into the airbox.
From there, it drips down on the crankcase, just ahead and above the swingarm pivot. It drips down onto the centerstand. (Yeah, it actually has a factory centerstand!) Then due to the angle, it drips down in a line.

...and here is the center stand, all nice and bleahch. At least it keeps the battery acid from corroding it.

Do carbs have a side-located drain screw for the float bowls? Or a single bolt on the bottom of float bowl?
Single bolt drain on carbs.

Just took the vent apart to see if anything was blocking the drain back to the crankcase, but no dice. I am changing the oil and filter anyway, so I will drain and carefully check the level when filling up.
The thing that gets me is that I have had the bike for almost 2 years and this problem only started in the last 2 weeks. maybe the oil additive I used made the oil too thick to separate from the vapor properly? I am going to refill with 20/50 since it has never been rebuilt and has about 48,000 miles on it. (Used to be Dad's bike.)

Since I havent had this problem until recently, and my dad said he never had this problem, (30+ yrs) I will assume that I hopped up the oil viscosity too much, and will see what no additive does.

...and thanks to all for the info!! I do appreciate it.

Rob Cremains wrote:

Do carbs have a side-located drain screw for the float bowls? Or a single bolt on the bottom of float bowl? Single bolt drain on carbs.

Possibly sign of a hidden danger here.
My understanding is that early Z1 carb floatbowls have no overflows (being similar in that respect to 29 smoothbores).
Edit -- WRONG! :blush: Z1 carbs do indeed have floatbowl overflows with drain nipples, whereas smoothbores do not. During production of 1974 Z1-A, the large bottom bolt was replaced with a side located drain screw.

If fuel starts leaking past a float needle and has no overflow exit from the floatbowl, the excess fuel can rise up into the carb throat and flow both ways, forward toward the engine and backward toward the airbox.
Either direction of excess fuel overflow ultimately leads into the crankcase.

Excess fuel flowing rearward into the airbox has a straight shot through the crankcase vent hose into the crankcase.

Excess fuel flowing forward toward the engine gets into the combustion chamber and flows down around the piston into the crankcase.

If the float needle isn't stopping the fuel flow into the floatbowls, and the petcock has been left open, the entire tank could conceivably drain overnight, with fuel getting into the airbox with some of it draining from the airbox drain hole and the rest of it draining back down through the crankcase vent hose into the crankcase.

Needless to say, fuel intrusion into the crankcase contaminates and thins the oil, which may have disasterous consequences.

Because of the above, the history as reported here regarding oil overfills is troubling, especially because of the sudden onset after all these years. Am wondering if maybe it was actually not overfilled. And that fuel intrusion into crankcase raised the apparent level through the sight glass.

And also wondering if fuel into airbox "rinsed" longstanding airbox sediment and passed with the sediment out through the airbox drain and onto the floor. And if the puddle is actually a mixture of fuel and sediment from bottom of the airbox. Plus further accumulated oil vapor settlement arising from the thinner crankcase oil.

Anyhow, the bottom line in this particular case is just wanting to eliminate the possibility of fuel contamination of oil inside the crankcase.

Would sniff-test the old crankcase oil, and carefully monitor the oil level and odor after the oil and filter are changed. Might see the level "rise" without apparent reason -- a danger sign.

Unfortunately, such problem may arise and continue during over-the-road riding (or while the bike is parked, as above noted).

There may be a method -- unknown to me -- whereby a leaking float needle/seat interface may be detected earlier on 29 smoothbores carbs without floatbowl overflows.

But meanwhile, here's how I addressed the issue with the 29 smoothbores on my Z1.

[Click on image to enlarge]





The smaller clear hose with the white fitting is from the airbox drain hole, and also routes to underneath the bike.

Hope none of this applies in the current situation. Will be happy to learn there's no problem with any fuel intrusion into the crankcase. And would also be happy to learn that any such problem has been nipped in the bud and corrected before causing any engine damage.

Good Luck!

Addenda -- During the 1974 Z1-A production run, various internal carb parts were changed, including floats, pilot jets, needle jets, throttle valves and choke plungers. Shape of the floatbowl and gasket was also changed, and choke operating lever was also modified. The most obvious visual difference is the smaller side located floatbowl drain screw which replaced the large bottom bolt. The 1974 carb changes began with frame number Z1F-032818.

Hmm. Nope, the carbs have overflow tubes, and all four needle valves and floats were just adjusted. I also have a couple of fuel filters inline between the tank and carbs, since I wasnt able to get ALL the rust out with electrolosis. Thanks, though, i will keep that fix in mind if it keeps up. I just changed the oil and filter so i will be going for a ride this week, and Ill let you all know!!

The problem of fuel rising too high inside the carb may be caused by a clog in a floatbowl drain circuit. So it's a good idea to assure the floatbowl drain circuits remain clear and open. And never hurts to sniff-test the crankcase oil.

All oem Z1 carbs (1973 Z1, 1974 Z1A and 1975 Z1B) have floatbowl drain nipples from an overflow circuit. Whereas 29 smoothbores have no floatbowl overflow circuit and therefore no floatbowl drain nipples.

Perhaps the oil leakage did indeed result from overfilling and maybe being forced out through the seals as well as the crankcase vent.

The original Z1 Owner's Manual emphasizes, Do not overfill the engine (page 18), and elaborates (on page 38) Do not overfill the engine. Too much oil will not only cause smoking, fouled plugs and throw oil into the air cleaner, but may eventually cause engine damage from carbon build-up.

Good Luck!

Edit -- This post is edited to confirm that oem Z1 carbs do have floatbowl overflows.

If oil is coming out the crankcase breather and getting into your airbox, there are two reasons:

1. blow-by past the rings
2. crankcase overfilled with oil

The oil pan gate probably won't fix your problem. The purpose of the gate is to keep oil from sloshing to the back of the pan under hard acceleration and starving the top end because no oil is available to the oil journals which are more up front.

I suggest you CAREFULLY check your oil level. If it is correct, a compression check dray, then using a bit of oil will tell you if the rings are sealing. If they are NOT sealing well, you would do well to check the cylinders for ovalling (out of round) using the bore measurement techniques suggested in a factory service manual. If the bores are out of round, honing and new rings won't help much.