Modern Vespa

okay. i was on my way home and i noticed that i was idling really
high and there was an airy noise. not super high to the point where
other people on the street would notice it, but higher compared to
what i normally keep it at. when i got home, i dismounted and tried
to turn the idle down. -fail. that and there was a sound that i
would describe as "letting the air out of your tires".

i checked the slide- it didn't always return to the same spot. took
out the carb, cleaned and replaced it.

cleaned the throttle stop screw and hole as well. i could take the
whole screw out and the bike maintained the same idle.

checked for carb and airbox leak by spritzing carb cleaner around the
base- nothing.

made sure that the carb was torqued down evenly.

checked the cylinder head bolts.

took the gear oil fill screw out- suction

topped off gear oil- idle at same level, still air sound, oil being
burnt in the engine (super smokey exhaust)

clutch side air leak? maybe? i didn't get a chance to check the plug because i was too flustered and it slipped my mind...

the kicker is that i JUST replaced the seals about a month and a half ago. actually, i did a lot of work about a month and a half ago:

new piston, cylinder rebored, all new kick assy. seals, cruciform, and cleaned and rebuilt the carb.

i had noticed that there were some bogging issues at about 30 mph but shrugged it off as not a worry b/c i was still breaking in the engine.

my city's rally is this weekend followed by a road trip to austin in which the plan was to trailer the scoots...

with that, i know i'm being a total antsy pants, but does anyone have anything to suggest that i haven't tried or any type of "band aid" solutions until i can drop the engine in a few weekends from now?

Am i blind, or did you never mention what your scooter was in that whole post?


If you've got suction in the gear hole, it's a clutchside seal leak.

The seal might not be BAD, but could have a folded lip on it or something that's allowing air through.

I would pull it apart and check it. I know it sucks, i know it's a lot of work ...

but i wouldn't want to ride in a rally ride with a cloud of smoke behind me and no power because i didn't change the seal.

I considered it once, the night before a rally ...and instead did a marathon 4 hour wrench session where i dropped the engine, stripped it down to the cases, rebuilt and had it back in the bike. 4 hours.

bah! i totally forgot to mention what i had! '79 p200!

24/24 carb
120 main jet
running a #7 plug
sito pipe

Firstly, welcome.. put your scooter and your location in your profile so people don't have to ask where and what.

The suction in the gearbox would certainly indicate a seal leak. Sometimes when someone is working on them, and doesn't lube the inside of the crank seal when they put the crank back in, it folds a lip over on the seal and doesn't make good contact. It's not uncommon.

I'm curious how one would detect suction at the gearbox fill... I opened mine up (since I've had some smokey smokey exhaust) and all it did was churn gearbox oil out (not surprising really). Seemed like any suction would be outweighed by the churning of the gears spewing out oil.

Figuring "what the heck, I'll already have to re-top off the gearbox now anyway" I drained all the oil to check for suction. Holding cellophane up to the filler hole it didn't really show any noticeable "suck" so I guess I'm ok and installed my new clutchside seal well enough *crosses fingers*

But still, I'm curious how you detected suction


Thanks!

that's what he said.

Hey, do you have any idea how psychologically debilitating it has been for me all these years to not know this!? Kids, don't skip health class!

You put your finger on the fill hole. If oil spurts out onto your hand smell it and see if it smells like gas. That's the other clutch-side seal leak test I know of.

If the clutch side seal is REALLY sucking in air as the engine is running (due to a severe leak ) you can put your finger over the hole ( after you drain the gearbox oil ) and you can feel a slight pressure release when you remove it.

Yes, the easy way is smelling for gas in the oil, and checking the quantity and the viscosity of the oil you've drained....

But you can determine severity of the leak through the amount of vacuum you feel.

It's been my experience on a couple different bikes that the gear oil level only has to be low enough not to churn out of the fill hole. Only when it's totally topped up can it sometimes hide the suction from the busted seal.