Modern Vespa

Smoke found a tiny leak at the cylinder base gasket for me on the white Stella just last week. It was like an inch-long gray arrow pointing right at the problem spot.

The mystery deepens then…

Thanks guys.

I suspect it's the area of "oil sucker" thinness - and I'll explain why - after I test.

What was you pipet test?

Ah I meant using a dropper/pipette with soapy water to find leaks instead of using a spray bottle. Spraying soapy water naturally creates bubbles.

paint brush works as well.

Appreciate everyone leaning in and giving best tips and tricks.
I've sprayed it, droppered it, brushed it, and smoked it.
Im higher than Tommy Chong - but there is no evident leak.

Pulled the fly wheel off - retorqued the center bolts.
Used all above methods and found nothing on that side.
Clutch side is a bear to get to - if I go there - I'm just gonna pull the engine.
The leak is sooo slow.
WTF?

To test clutch side - I rigged up my own set of new tests.
1. I created a fitting for the crank case breather hole - so I could attach a rubber tube to it. Then I put that tube in some very shallow water. Not so much as a pin sized bubble came out when I pressurized the case.
2. I then took a second pressure bulb - attached it to that tube - and pressurized the crankcase. This time - I watched the other pressure gauge to see if any pressure from outside could get in. Again - not the slightest.
Idk - tests seam to show its not coming from the cases.
Just seeps out so slowly - maybe I should get a new o ring for the test equipment...
Not sure what to make of it.

That's a bummer that it's still a ghost.

You're one step away from dunking the engine in a tank of water.

Joking aside.

That's still a pretty good leak the speed that it's going at.

With the gearbox side test, it'll take a quite a while before bubbles appear because the leak is so small for air to be pushed out after filling such a large space.

Maybe a leak with the pump/gauge equipment?

I usually use a finger over the hose/adaptor/gauge to make sure those are airtight before fitting it to the engine.

Stumped.

Purpose of gear case breather test was to try and expose a leak without pulling wheel, clutch cover, etc.
If they come off - its going to be with the motor out on the table.

I can't rule out clutch side leak - but if it exists - it is very slow.
Ha! That leak speed seems very slow to me.
Sounds like you have experience of that level of leak being significant to operation.

As aggressively as I pumped air into the crank case - I would have thought it enough to at least make the gauge connected to the inner volume, blip - even just a hair.
There was nothing.

I'll focus in on the head next.
Test equipment appears to be ok - but will have to devise a better test to ensure there's nothing weird happening with it.

That's a good point, a leak that slow, you'd wonder where in the running would it affect jetting/temps?

But the speed of this leak, I'd still be looking for it for peace of mind.

Red PX
https://youtube.com/shorts/cDOwZG_8LIg?si=_KnalBB38oQnrTJj

The leak here on this red 210 still ran. 90% certain it's clutch seal leak. The owner didn't want to deal with it, even after all the red flags it means. The power was terrible, but didn't over heat because jetting took care of it. Ridable, but not much better than a stock bike.

Black largeframe
https://youtube.com/shorts/HWtohp6NSHI?si=4mvGQRobPSuC3JMv

This one seems about the same speed as yours, intake manifold leak.

Egig170
https://youtube.com/shorts/md0Nwc7YOLg?si=kmhv6JeDQ1RC9fOi

For my own engines (this is on the egig engine), zero needle movement. At least you know it's rock solid and any jetting is reliable.

Did you remember to cut the gasket nibs?!?! Longshot.

IIRC, you sealed the living shit out of your case halves with hondabond or some such, so probably not the issue, but cutting the nibs off the case gasket helped on the Spanish.

I cut the nibs off at birth - it's more a hygiene thing than religious.

I've been thinking of your hunt to find the leak.
I'll go at it one more time with it in the scoot - then decide if it's worth pulling motor for at this point or just ignore it until it gets cold and rainy out.