Good, I've been putting a lot of miles on it until recent rains.

I have been investigating a puddle of oil under the carb. Looks like I got carried away when I started ripping out unneeded components. In think one of them was an OEM oil catch can that was holding and returning oil to the valve cover area.

I tried using a longer run of tubing with a filter at the end to see if that would hold the excess while running. I revved it out on the stand and it seemed to work fine, but when I rode it at WOT it puked out the filter. So I think I will try the hamster bottle catch can mod as described on prodawg.

If originating via the valve cover vent . . usual suspects are too much engine oil, or excessive piston ring blow-by. Consider experimenting with adding 1 tablespoon (½ ounce) of 2-stroke oil per gallon of gas, unless you are already using 1 ounce per gallon of Seafoam. The supplemental top end oil may, or may not, reduce blow-by.

Material Safety Data Sheet comparisons . . .

Seafoam per MSDS:
Pale Oil 40-60%
Naphtha 25-35%
Isopropyl Alcohol 10-20%

Berryman's B12 per MSDS:
Toluene 40-50%
Acetone 20-30%
Methanol 20-30%
Methyl Ethyl Ketone <5%
Isopropyl Alcohol <5%
2-Butoxyethanol <5%


If origination is unclear, another scenario . . .

http://www.youtube.com/watch?v=ttD9zE2791E

I may have also messed up when I was deleting the PCV (?) setup. I watched some YT vids on vacuum line simplification and may have misunderstood. I routed what I took to be the crankcase vent (in the right in this pic):

http://i722.photobucket.com/albums/w...ps6one6afd.png

... back to the airbox snorkel running from the filter to the carb, not realizing oil could get in that line. I think the oil was pooling in the snorkel and dripping out of the tube/snorkel interface onto the top of the case. Which would imply a leak there. [also, I just rewatched that video, and he ran from the PCV port to the air filter, not the snorkel. Perhaps that would result in less vacuum pulling on it.]

I pulled that end of the snorkel, observed oil in it, cleaned and replaced/tightened. I have not run it since I made that observation as it's been raining and I have been researching.

I'll drain and refill the case with a known amount of oil so I will have a good baseline. In the meantime I ordered a catchcan. I will also try the oil additives you recommend. I assume that would show improvement if the problem were with the piston rings.

Next day off is Tuesday, so I will work on the oily issue then. I am suspecting overfill since I tend to fill to the top of dipstick crosshatches, and my recent reading suggests GY6 engines like about halfway up the crosshatches.


Thanks for everyone's input and interest.

What did you find on Tuesday?

Confusion.

I drained the case and added a measured 800ml. This took it to near the top of the hatchmarks on the unscrewed dipstick. Nothing foreign in the strainer or on drain plug.

Installed the catchcan on a dipstick adapter for testing; if it worked I'd move it to the valve cover breather.

At idle (and with the valve cover still vented with a 2' tube) there is so much pressure that oil was pushed up about 1.5' up the new dipstick-attached tube, just short of the catch can itself. I revved it and oil blew out of the top of the catch can like a water hose. I would say at least 400cc was ejected in a couple of seconds.

Could blow-by really be causing this much pressure? Maybe there is a blocked oil passage and the oil pump is forcing oil out some other path of less resistance?

If blow-could cause monster pressure like this I guess I need a compression tester to see how the piston is doing.

You could also try a fitting that screws into your spark plug hole, and accepts an air chuck. When you pressurize the cylinder, any leakage will be evident. You need to turn the crank to TDC to perform the test. Air rushing out the muffler is a leaking exhaust valve, air blowing back through the carb is a leaking intake valve, air coming out of the dipstick hole is rings. Expect some air to come out of the dipstick hole, because of the ring gaps.


You can make your own adapter by breaking the ceramic off of an old plug, and then welding or epoxying an air chuck fitting to the threaded body of the plug.

Some bikes do generate quite a bit of crankcase pressure. I recall someone forgetting to put their oil cap back on a KLR only to get a leg full of oil... Unless that's because the clutch is right there on a KLR?

I ordered a compression tester and will let everyone know what I find out.

Ok, I got a compression tester with 10mm adapter and an attachment that will allow me to blow air into the sparkplug hole. So some new pieces of information.

1. Cold engine has 125psi of compression.

2. adding .5ml of oil manually bumped it to 128psi or so. Certainly not a big jump.

3. blowing into the spark plug hole with 60psi caused the engine to turn over

4. when it came to rest from #3 the air came out the exhaust

5. when I put my hand over the exhaust while injecting air I got some oil to rise up the catch can line. Releasing my hand dropped the oil again.

Am I any closer to a diagnosis?

Try turning the motor to TDC and holding it there with a socket and breaker bar; repeat the compressed air test, and see where the air goes. My guess is out of the dipstick hole.

Correct, out the dipstick hole which is currently holding the catch can tube.

Does this narrow it down to a compression issue?

I ran a little camera-on-a-wire thing down into the cylinder. It looked like there was still crosshatching on the walls and no other scratches. Piston was carboned up, probably from the oil dumped into the airbox before I figured out there was overpressure.

Save me from going back through the thread; could there be a blockage in the vent tube?

No, because it was originally blowing oil out that vent tube. That's why I got the catch can and mounted it on the dipstick side.

I haven't pulled off the valve cover since this started happening. Maybe I should do that and look for broken parts and repeat the pressurization test.

I expect pressure to leak past the rings and blow into the crankcase, but a minor amount. Maybe a ring was broken on assembly, which explains the decent crosshatch.