Modern Vespa

I'm having some weird symptoms as of late. When it sits for a few hours or overnight, the gas lined doesn't seem primed any more. It takes about 3 kicks to start which I know isn't too bad, but the first 2 are totally dead dry kicks like it isn't even trying. About half way into the third, I feel it pop real strong like the fuel primed and it starts immediately. Then push in the choke and it seems fine. However, after it warms up, if I idle at a red light for a little too long, it'll bog kinda hard on first pull for just a sec. And then it'll catch up and ride just fine after that. Also, after it warms up, if I park it and cut if off for about 30 min, it'll be real hard to start like it's flooded. It's not really, really bad, like I don't have to lean it to get it going, but it takes a good 6-8 kicks and pulling the throttle to get it going again. But again, if I let it sit for much longer, I think the excess fuel drains/dries up and it'll start like I explained above. Thoughts?

Octo

Clutch side oil seal worn out?

I did a rebuild only about 1100 miles ago and that included new seals. I suppose the seal could be faulty. What's the best way to check?

any traces of gear oil on inside rear tyre?

Crankcase pressure test is the best way.

When the seal leaks (or case gasket) the gear oil is always affected. The level goes up or down. If you drain the oil and see what it looks like and how much there is, should give you some idea . If ok re fill it, then check the level a few times before riding over a week. If the level hasn't changed in a few hundred miles the seal is most likely good enough.

As you have rebuilt it only 1100 miles ago the oil level should be exactly the same as the day it was done.

Jack: Having an easy way to confirm that my seals are good appeals to me. Looking for signs of oil behind the flywheel & stator for the flyside seal, and at the rear wheel & hub for the rear hub seal is easy enough to know if there's a serious problem, but not so easy w/ that clutch side seal. What about a hose on a fitting into the clutch cover vent hole to see if the clutch/gear box side holds modest pressure? Worth a shot? What would be an appropriate pressure? edit: To be clear, because I've never done it, you mean pressure into sparkplug hole w/ blocked off exhaust and intake? What pressure held for how long?

The clutch vent does seem like a good idea for a pressure test with least faff but quite easy to do more damage as pumping against the seal. On the old Vespas with outside main seal it's not such a risk but would be interesting to know what pressure a PX seal would pop out at.

A pipe on a fitting at the clutch breather (or oil filler with breather covered) would be a worthy test to check a really bad seal. Just blow in it with your mouth. If the seal was torn or missing, you would hear hissing at the carb.

Hat tip to blackbart. Length of fuel line attached to 7mm fitting screwed into clutch breather hole

I'm in the middle of a move right now so unfortunately I've been too busy to take a look yet.

I did change the oil few times already to keep a good eye on it and it never seemed to be too much or too little. I didn't really measure it though; was just eye-balling it.

Cool idea with the balloon trick. Will give it a go after settling in to my new place.

Thanks Mike, I missed that. The balloon makes perfect sense plus should be much easier than testing from the crankcase side.

Yeah, blackbart is one crafty dude.

That's actually a pretty demanding test - it pressurizes the whole gearbox ... clutch seal, clutch cover o-rings, rear hub seal, the kick start seal, the selector box gasket, the main case gasket - even the oil fill and drain bolts (and the auto lube spindle if you have autolube). I'm surprised his engine held for 15 minutes. I don't think my engines would pass. Let us know how yours do.

Add a worn batwing shaft to your list of things this thing should be able to detect. If the balloon goes down you'll still need to figure out where it's leaking but now we have a list of suspects.

Actually I have most of it already, just need to add the ballon. When I tried it a few years ago, I did as Jack suggested and it seemed to hold my lung pressure OK, but hard to know the leakdown like a balloon will show. I'd like this thing to 'find' a known bad clutchside seal to know it can be trusted. Will keep you posted

Make sure your choke is fully open and not sticking. Happened once to mine. Same symptoms

Hey again. Was out of town for work stuff. And like I said I also had to move. Things have been crazy lately. Anyway, just now getting to post an update. I see oil drips after letting it sit a few days. Also some on the rear wheel. I drained the oil and measured it as well: about 180ml. Seems low. I'm pretty sure there's no gas based on comparing the viscosity against new oil and because it doesn't really smell like gas. Haven't gotten to do a pressure test yet as my new garage is a total disaster at the moment. Few pics for your perusal:

octo

Ok, so I'm convinced this fitting you describe does not exist! haha

I've gone to Ferguson, Fastenal, and Grainger. All have said that a fitting with 7mm threads is something they don't carry nor do they have any idea where to get one. Where do I get this mythical item??

I'd rather not break the cap off my breather if possible. I tried a little bit but it's welded pretty good and it'd be hard to break without damaging the threads it seems.

Thoughts on how to do this?

There are other ways to determine if seals are leaking while you look for items to do a pressure test.
Clutch seal will leak and gear oil will smell of gas after running the motor for a while.
Rear seal is behind the rear hub so just take it off and see if oil is leaking or in the hub.
Flywheel side seal will have oil on the outside of cases after removing flywheel.

Well I have a simpler idea. I just recently had to do this to my p200 engine. It had a few of the same symptoms as you have described. Biggest problem was that it flooded when I tried to start it up. I went from 1/2 a kick to get it started to 12 kicks. The carburetor seat would not seal, so it always seeped fuel. A new needle did not work, the seat had an issue. Anyway mine got progressively worse. I replaced the top of the carb...problem fixed. Just a FYI