Modern Vespa

I used to think i was a smart person.. but i cant know everything.
Ive got an Italian, 50cc 2 stroke…horizontal Minarelli.
It has a remote oil tank and a crank-driven oil pump.
It sat for years… i acquired it and got it running with the help of a member here. (He's been great! Wish we were neighbors)
But he's not my personal tech, so i want to ask the group..
Recently, for various reasons…largely that it stopped running very well…
I checked the compression and it reads 75psi.
I'm pretty sure thats waaayy low.
I suspected a failed oil pump, but I'm not certain. I disassembled, reassembled it and it pumps…allowing air, at least, to flow. Maybe it was plugged before..dont know.
(Pretty simple device, actually)
So I pulled cylinder and it has some slight scoring aligned with ring ends.
Barely discernible with my finger nail, but scoring nonetheless.
Is that enough to reduce compression significantly? Yes, it does run..mostly.. assuring me that the rest of the process is working..spark, etc…
Before i replace the piston and cylinder, per az_slynch, where else might there be a 'pressure escape'?
Any suggestions are welcome.
Thanks all!

If the marks align with the ring lands and you can't feel them with a fingernail, it may be OK. Please post pictures for review.

If you have a compression tester like the one below, put a dab of grease on the adapter threads and run in down by hand. When it stops, put a wrench on it and add at least a half-turn, possibly more depending on how loose it feels.

Put a thin skin of grease on the O-rings of the hose assembly. Screw it into the adapter by hand; the hose will be a bastard from being stored in a curved state. Twist the hose until it seats firmly. Then connect the gauge.

Disconnect the vacuum line for the fuel tap and cap the vacuum port on the intake manifold. Twist the throttle wide open when testing compression. Crank it over via the starter or kickstart until the needle stops climbing (~5 sec on the starter).

As for the oil pump, have you checked the worm drive gear assembly yet? It's accessible if you pull the fan cover, the fan, the flywheel (27mm left-hand puller needed) and the stator plate. There's a gasket behind the stator; if you carefully lift it with a plastic knife, you can probably reuse it. That well behind the gasket holds the pump worm gear.

The gear held on with one snap ring and is driven by the crankshaft by a single pin. The whole thing is lubricated with white lithium grease. It the grease is dessicated or absent, the plastic worm gear will get chewed up while driving the pump gear. Check for plastic shavings. The drive gear is the same as an '02-'11 Zuma 50. Part is still available from Yamaha, per Partzilla.

For additional details on the pump, if there's oil in the tank and the lines are connected, does oil gravity feed out of the pump if you loosen the bleeder screw (#2 in the attached parts diagram)? We're looking for obstructions in the line or the tank screen (if present). If it's good, put oil in the line to the carb as well and let it bleed from both sources for a minute or so. You want to ensure there's no air in the oil lines.

Finally, for the record, which oil are you using the the autolube system?

Im a mechanic by trade and also have a horizontal Minarelli. Like you, Az_slynch has given me extremely sound advice with my build. My scoot now can achieve 60mph on the straights no wind, verified by GPS. I recently saw 70mph in a tuck downwind.

Stock 50cc top ends are cheap and I totally agree with his decision. A leak down check is always a great idea to spot trouble before and after a new top end. Those autolube pumps can fail or work intermittently so keep that in mind.

I work on aircraft and have been tuning motorcycles since Jr. High. I wouldn't be asking advice from Sean unless he knew more than me and had the experience to back it up. Besides, he's a stand up guy to boot. Thanks Sean!

Ok.. damn!
Alot of time spent on that reply!
I'll get into it and see where it goes.
Oil is Motul 8000 2T synth.
While i reassemble and do compression check, as advised, here are some pics. The worm gear feels complete and it does turn.
And, i'm not against simply replacing the bits, i don't want to have overlooked something. And if i can get the thing to rip without requiring more upgrades, i'm good with that. But more power can require beefing up other parts. Been there with a big 4 cyl Suzuki GS1100.
This whole thing began when it seemed to lose most of it's power one eve so i assumed lack of oil in the mix. But it never seized.
I'm going to remove and bench-test the starter again also. Something down there makes a crunchy noise when i press starter button. The starter spins though.
Thanks folks!

Cylinder looks decent. Seat each ring in the bore individually. Push it down the bore about an inch with the piston crown and then back up to within 1/4" of the top of the bore measure the ring gaps and share your findings.

Motul 800 is premix only; it's not meant for autolube. You can run 710 and it's more than adequate for this engine. Heck, my buddy swears by Honda GN2 in his modded Zuma and it just plumb works.

Technical Data Sheet for Motul 800

Crunchy noise could be the starter gear bearing. Pull the variator. Behind it, there's a starting gear with a roller bearing inside it that is lubed with lithium grease. When you pull the gear, there's a one-way clutch that fits on top of the gear and is splined to the crank. Pull the gear off, leaving the clutch on it. If you pull the clutch, the three rollers, spring covers and springs will shoot off someplace. If you want to pull it apart to clean the belt dust out, place the gear and clutch in a gallon-size Ziploc before separating them. If you lose parts, Partzilla still sells everything but the starter gear. See the attached image

1". ——- .25" +/- .0005
Top end gap: .007. .006
Bot end gap: .007. .006 I ordered the 710. I guess the 800 I'm using is too thick? I use it in a pre-mix 40:1 Motron-Minarelli V1. Of course they will. I almost immediately go look at the end of my driveway when things sproing away. But my hand, while engaging starter, tells me that the crunchy sound is coming from that area! I'll get the top end together first. And i think by now, i should simply do the cyl/piston. Athena parts are ordered from Italy? Yeesh!
Thanks Sean…and BajaRob for the added endorsement!

Also, Sean, before I order a kit, do you know if the stock plastic cover fits over the Athena barrel? I prefer the stock look.

Ring gaps look to be within standards. I'd have trouble blaming the piston/rings at this point. I'd be wondering if the starter clutch is buggered and the scoot is down on power because it's dragging the starter motor along when running.

The stock cover fits pretty much any air-cooled (AC) horizontal Minarelli cylinder.

Mille grazie! I sooo appreciate the help.. information.. and the guidance while I'm learning, always!
I'll reassemble, change the oil type and investigate the starter.
I have replaced the belt, rollers and those bits.
Ooohh! It just occurred to me..! I wonder if the drive 'pulley' has loosened?!
Damn!
I'm grateful for this forum… wish i could offer help back.

You are helping back. By participating in this troubleshooting dialogue, we're both working to resolve the issue and we're documenting the details for the next poor soul to run into this sort of problem.

az_slynch no scooter work yet. You know how life (and in VA, weather) goes. We had a nice day, but i took a couple other bikes out for a spin! Including this Motron. (Yes, i know. These are not Modern Vespas, but I do have a GTS250!)
😊
The proper injected oil (Motul 710) arrived today. its much thinner and gravity-feeds through the pump bleed hole.
I've pre-mixed, in the past… had a Suzuki RM125 that screamed..but not dealt with an injection system.
The Motron Minarelli V1 is a 40:1, pre-mix.
I think you've got me looking in the right direction. Tomorrow, i'll pull the CVT side and look at the drive sprocket and starter gear.
Thanks for help and patience!

How to test a Minarelli oil pump, according to Eton.

https://get2itparts.com/_zz_etonamerica/PDF/WP/WP0024.pdf

Motovista Ahhhh yes!
Great idea. Bypass the pump by pre-mixing and verify that it's doing its magic.
I shall!
Today, i got called away to service a garden tractor. Priorities.

Y'all are good peoples!
😁

Update:
Oil pump does pump and drip per the provided Eton spec… slow, but it drips. Since i can push a tiny wire through the carb nipple, I'll infer that the carb is sucking the oil in.
Engine starts and runs.
I pulled the variator cover to see what might be anomalous under there.
I found a 24 g gold nugget tucked inside. I figure that doesn't belong so i threw it away.
Still reading?
The starter shaft and those gears on the crank 'seem' ok.. no torn/worn teeth
I had installed a new belt and rollers in June and it ran fine then.
I removed the front pulley and belt to see if anything was awry… it all looked good.
Started it up.. engine revs up…belt tightens.. wheel spins.
Its smoking a little, but its also pumping oil as well as having a 50:1 mix in the tank, for insurance of oiling. I'll drain that gas after my road test. My Stihl tools can burn it.
"So? Test ride?!?"
Yes, after i assemble all the plastic bits to make it street-able.
(Makes me like my moped even more… few bits covering the moving parts)

At this point, the only thing different has been the oil i was using.
There is a visible difference in viscosity, for sure.
Thanks for pointing that out.
I'll re-assemble and test it on the road today.. with my 185 lb load.

More clues:
It only starts if i block the carb opening.. choke the heck out of it.
It will run… until i put the airbox on and cant block the carb opening.
Then it just doesn't start.
Hmmm.
Requiring all that choke means too lean mix.
Air screw out 1.75 turns.
I'm soaking the entire carb and testing the electro-choke.
Ok.. so before 'someone' reminds me to simply toss the Gurtner carb, and because i do like to figure out what's wrong.
Maybe THEN, I'll toss the Gurtner.
😁

I'm not re-reading the whole thing - but you have checked the inlet manifold isn't cracked?

Doh! No, but since i'm looking at everything else, i shall!

Essentially, it just lost power one evening. I can't associate it with anything i had 'touched' immediately prior, except the wrong kind of 2T oil for the injector.
Right now, the carb is soaking, so I'll unbolt the manifold and check reeds at same time.
Thanks for the tip.
I'm over-documenting, but as it was pointed out, maybe the details will help another ET2 or any 2T rider.

Can i borrow a towel? I throwing it into the ring.
Removed and cleaned everything from case up.. i see nothing awry.

So after many hours spent, and lots learned, i'm done debugging.
az_slynch suggested a new Athena top.
I think I'm going that route. I got it to start and idle and rev up and down and idle.. then, after a few minutes, it dies and resists starting again.
I can't find anything i can 'fix' and i actually want it to be usable again.
I can only guess, Sean and BajaRob, that running with the thicker oil not flowing so well, the cylinder has been ruined enough.
Next time I remove the cylinder, piston, it will be to replace it with fresh.
🙁

I know it's been a while.. and y'all are anxiously waiting for results.
Ok.. first, i took a 2 week west coast tour on a hired BMW. We flew into LA.. and, after stopping at the Quail in Carmel, we continied up to Portland.
Back to the Tiny 2T. Verbosity for future readers with similar issues…and because, well, I'm me.
I did replace the barrel and piston with the recommended Athena piece.
While R/R and thoroughly cleaning the carb, the little brass tip on the e-choke broke off. However, i merely installed it as is. Its only an issue on startup…bit it does start after some cranking.
I've located an aftermarket replacement, but in the meantime, it's now running again.
I replaced the reeds also and thoroughly inspected the manifold for cracks.
The air-mix screw is out about 1.5 turns and it seems ok.
I'm not reassembling the entire body until after i receive the new e-choke. It's a 30 minute ordeal that is annoying.
Also, it takes a minute or so of cranking to start and i dont want to wear out the little starter or those associated parts.
For now, though..i'm declaring a success.

What was the issue!? Im not 100% certain.
I'm only guessing it was the wrong oil that was too thick for the injector?
Or it remained sticky in the carb.. slowing down atomization.. and burn?
Thanks for your input!

More..
I received a new, replacement bystarter (proper term for the e-choke), plugged it in.. bingo!
I'll wait a day or so, do a couple more cold-starts before i put the body back on.
I found a part supplier in Houston that is knowledgeable and priced reasonably.
While others may 'fit', i'm confident there is a functional difference between the 2T and 4T applications.
The one i plugged in worked.
Also, they do require voltage in order to work. But it needs AC. The engine needs to run to generate enough current to heat the gizmo inside.

az_slynch recommended a Dellorto carb, i cant find one. The Gurtner 12y is doing it's thing for now.

I dispute that it needs AC. 12V AC RMS from the regulator (which is roughly what should be supplied to the auto-choke - where did 'bystarter' appear from?) is exactly the same power provider into a resistive load as 12V DC.

Ok… i will relent and allow that what i read was inaccurate. Y'all be smarter than i, sometimes.🤣
But without engine running, the wires show no voltage.
Where did i acquire the part?
From a place called Global Motor Imports, in Houston, through Bezos.
Much internetting suggests that the name for the e-choke, is bystarter..dunno why.
And it has same affect as a choke, but works in reverse. It changes the air-fuel mix, for sure though.
It allows air to flow across a small port, sucking more fuel, until it warms up. Then the needle drops and blocks that extra port.

This guy explains it pretty well. Images missing though.
https://www.modernbuddy.com/forum/viewtopic.php?t=27646

Edit: spelling and added a link

Hey all, i need to post an epilogue here.
Thanks for your help and patience. I know its not a Vespa, but scooterarmy doesn't want it either. (Although they're great with my Motron Medalist)
😊
It seems there are minimal resources that focus on this little critter.
Shaun, at Myron's has been a good help for sure.
Anyway, per az_slynch , posting the details here may help someone else with a Malaguti Yesterday and the Minarelli 50.
I've wrapped it up.. done.
Air screw is 1.5 out, stock Gurner 12y, Athena aluminum cylinder and head with their piston, still 49cc.
The oil pump seems to be fine. The issue, i believe, was i correct oil.
I'm now using Motul 710, getting the factory-spec drip-rate a d i ise e-free, 89 gas.
Today, i got a GPS 43.5mph. More is better, but im happy.
It starts and runs!
Thank you.
Now, into the GTS250!