Modern Buddy

Help me out guys, what haven't I checked? My scoot is generally a one-kick start.

I rode to work today and back home with no problems. Right as I came down the hill the engine cut off and I coasted into my driveway. It was like the key was turned off or the kill switch pushed. She just stopped running suddenly.

- I checked the fuel tap and put it in Reserve just in case.
- Still nothing on kick.
- put more gas in just in case
- Pulled the plug and had spark
- pulled the wire off the kill switch anyway
- still had spark
- re-installed wire, pressed the kill switch, spark gone
- released kill switch, spark returned
- checked compression and it seems good.
- Used the timing light, spark was right on the timing mark
- Pulled the fuel line and gas ran out
- checked the fuel screen, it is clean
- Changed plugs anyway, kicked a few more times
- Pulled the plug and it was wet.
- pulled the jets, they are clean.
- But I still have spark....

What else needs checked?

Check compression with a gauge and see what it actually is.

You can also try this "cheat". Put a little oil in the cylinder thru the spark plug hole. This will help seal any issues with the rings and raise compression temporarily. If she starts and dies, or wont restart, then you have low compression. This works when you dont a have a gauge

Already used the gauge. The compression gauge registers above 120psi.

Exhaust plugged up maybe? Not letting her breath

If it were the stock exhaust.... but a SITO+ with less than 400 clean-burning miles on it. I wouldn't think so. A plugged exhaust would be a slow decline this was like a switch.

If a crank seal fails, how do I check for that?

Generally the easiest way to check a crank seal is to have it running first, and do a spray test to see if the rpm moves. Try disconnecting your kill switch entirely, from the blue and black two wire socket under the horn cover. When that switch starts to fail, you'll have spark, but it's weak and inconsistent. Super common with Stellas. Barring that, is it possible that the flywheel walked on the crankshaft, and now your spark timing is off? It's supposed to have a woodruff key, but if you have spark, and compression, you should be getting a hint of fire from the cylinder. What does it do if you hit it with some starting fluid on the air filter?

I pulled Stella out into the open and had more help this afternoon (and less beer). I cleaned off and painted the timing marks. I thought the vane (painted white) was supposed to line up with the A mark. I'm just cranking it over with the kicker lever.

Could the plate have moved or the woodruff key sheared?

Am I looking at this right?
https://www.scooterhelp.com/tips/timing ... iming.html

Not sure on the timing mark orientation, but if the key sheared, the whole flywheel can absolutely rotate out of place. I'd suggest pulling the flywheel to have a look.

I second that idea, yank the flywheel and double check the key. Atleast then you will know for sure its ok or not ok. Seen many lawn mower engines sheer their key for no good reason. Usually beat my head against the wall trying to get it started then pull the flywheel to find a sheered key.

So, I got the flywheel off. The key was not sheared. The magneto plate was not loose.
Timing was not to spec according to the stamp marks on the shroud.

I attempted to find TDC by normal means of finding the center between two stop points in the plug hole to verify where things were. By those measurements the timing looked more reasonable.

I removed and blew through the exhaust. It seemed clear.

By some miracle (still unexplained), I managed to get her started. It was not an easy process, but it ran. I blasted up the hill outside my house. It ran as it always has when running correctly. At 3/4 of the way to the top I heard some strange noise. I couldn't tell if it was coming from the back or the front of the scoot. I could swear it was coming from the front. At the same time the engine died and would not restart. Still has spark.

So what was the noise prior to the engine stopping? I couldn't say at this point. Removal of the horn shroud yielded no clues. No wires were skinned. The kill switch kills the spark, releasing it the spark returns.

I am sufficiently baffled.

I need a beer.

Issues with the reeds maybe? I agree, I think we all need a beer on this one.

I forgot to mention, I removed the carb and looked at the reeds. They looked intact. I suppose a broken reed would be visible.

If I gently pressurized the combustion chamber (via the spark plug hole) with the exhaust port blocked off, the reeds seemed to retain the pressure.

I don't know anything about Stellas but could it be the ignition coil or stator?

I do know from 20 years experience with 2 and 4 stroke lawn equipment, you can have spark when testing or even with a test light inline while cranking/running. But...under compression inside the cylinder there can be intermitten or no spark. This is from a weak CDI/Coil unit. Not totally failed but weak enough to only break down under compression pressures inside the cylinder. If you can source a known good coil, I would try swapping that in as a test. I think you have about eliminated everything else from skipped time, to compression loss and you have spark under test but no start. A different coil and fresh spark plug would be my next step if it was my engine.

I checked the compression again. It ain't good folks. Whatever that noise was it was bad. Now the compression is only 40 psi.

Does the cylinder come off without pulling the engine from the frame? I think I've seen that on other Vespa models. Does it clear the frame and head studs alright on the Stella?

Yes I have done it several times remove head then lock two nots together to remove studs remember to measure each stud before removal because mine when put back in screwed down further than needed not leaving enough thread protruding above the cylinder head especially the one where the air duct cover bolts to. If I remember rightly all studs are same length but make sure you keep them the right way up as I think thread lengths are different top to bottom. Barrel has to be turned slightly to remove and replace but ring's don't get stuck in the ports. Also you can only extract the piston pin from the outside as it won't push through. Remember to use new circlips. If I find my dismantling procedure in pics I will send you a link sure they online somewhere

Both rings are broken with pieces embedded in piston.

I'm thinking new stock piston and cylinder kit, keeping reliability in mind .... and stop racing around like a lunatic.

What do the guru's think?

What's the most likely thing that caused the rings to go and have you checked the reed valves not broken and may have caused it

At this point the engine is going to have to be pulled to search for debris anyway. Its just if I want to do it myself, or see how much my ignorance will cost me at my local shop.

Everyone thank you for your good advice through this trial.

So... return to stock .... or cylinder upgrade .... mmmmmm

Do it yourself. I bet you could do a better job.

Here ya go:

https://youtu.be/o3gG58j1ByA

You just need to follow along. Couldn’t be any easier.

The problem with doing it myself is when to stop. Doing the best job you can do for me often involves going too far. I'll probably end up wanting to replace the seals and everything. I will only be able to work on it for a couple hours at a time and it will take all winter.

If I let someone else do it, then he'll do what he's supposed to do and give it back in a reasonable time.

I'm still considering cylinder kits at the moment. I still may do it myself.

When you're looking for someone to fix your motor properly this maybe an option. http://www.scootermercato.com/Garage/Engine-Rebuilds

A bench tested rebuild from an actual trusted Vespa mechanic that's repaired Vespa's for decades at $400 plus parts is the best deal I've seen anywhere. If you can remove the engine and fluids they provide instructions on how to ship and send you a shipping label.

I'm settling on the DR177 kit, doing it myself, and considering which main jets to buy.

Current setup that was just about right for the stock cylinder and SITO+ exhaust was:

Stock 20/20 carb
55/160 idle, 160 air, BE3 atomizer and a 100 main jet.

I was thinking of trying 106, 108, and a 110 main jet.

If anyone else has this setup, open for guru guidance.

Have you checked to see if the cylinder could be rebored for an over-sized piston? That way you could keep your current setup.

If you go with the DR177, I think you’ll need a 24/24 carb.

The original cyl wall is chewed up pretty well, Dave. The original head is worse. This was my chance for Stella to gain some cubes, so I'm taking it. (got the nod from the wife)
I've got some hills where I live. I'm not so concerned about top speed, as I am about torque to climb hills.

I've already called ScooterMercato and placed the order for the DR kit. It will be an adventure. If it turns out after experimentation I need to go to a 24/24 carb, then so be it. Since I posted here, I've been sifting through other forums. Some guys are saying they are running the stock 20/20 after adjusting the jetting. There are discrepancies with exhausts and such, so it isn't a clear-cut solution to what exactly needs to be done for jetting so far without honest experimentation.

I did see that the stock 1970's Rally 180 Vespa ran a 20/20 with jetting very close to what I've got in mind. I guess I'll start rich and move back if needed. In a phone call to David @ ScooterMercato, he suggested to me to start with a 112 Main Jet and work from there.

http://www.scootermercato.com/s.nl/it.I/id.41/.f
This is a database that some of the customers have added to. There's nothing in there that's the same as my planned setup, but its somewhere to start. ScooterMercato would hope that other tuners would contribute their successful builds to the database.

I'll look at adding a CHT (Cyl Head Temp) sensor as others have made that recommendation.

We will see.
Adventure Ho !!!

Have you had chance to find out what caused it yet Eric?
Most of those in the know have all suggested the 20/20 carb unless going the whole hog of porting etc.

Air pocket in the oil feed line maybe? Did the check valve in your oil pump fail, and let air back out into the line?

The oil line was full. I've noticed the oil drains the other way (into the crankcase) if it sits too long and the tank is too full.

I'm starting to think that the root cause was previous overheating damage. There was a big mouse-nest in the engine when I bought the scoot. I'm wondering if the engine was repeatedly overheated prior to my cleaning it out and weakened the compression rings. I didn't find the mouse nest right away either until I realized the engine was running hot.

On the path to rectification. "No replacement for displacement," as they say.

There's no mention of any sealants used during the cylinder install here. I know the DR kit has no head gasket. (unlike the LML stock head)

So should it just go together dry ???

http://www.scooterhelp.com/tips/engine/ ... vespa.html

Thank you all for your support.