Modern Vespa

This is good to hear. You can get away with doing just a motor rebuild and replacing the wiring harness. Replace the bearings and front brake shoes and you're good-to-go indefinitely. Hah! You've come to the right place then. We'll have those around you wondering about your sanity, or at least your risk tolerances, in no time!

I have my SprintV's motor in my VBB and used that to go plaid, so you can definitely get plenty of go-fast out of a Sprint. It's a little over 17 HP and would push about 70 on 10's. The fundamental parts changes are a 24/24 carb, a BGM 177, a SIP Vape Sport ignition, a SIP Road exhaust (I forget if it's a Road 2.0 or XL right now), and a cut 60mm crank with a PX cone (so it can use PX ignitions). Past that, it's all just setting it up right.

I'd say get a successful rebuild under your belt and maybe even look for a second motor to use for tuning. Not everyone is a fan, but you can build a crazy-fast motor on top of reeded LML (Stella) cases.

Although as I'm now learning, smallies are where some of the craziest power is at, albeit with a different curve. Or a P200 motor...VMC245, I'm lookin' at you...

Dude, I've been following your small frame thread and it sounds awesomely terrifying! I just want plenty of grunt to get up and go with 55 mph traffic and to climb hills in my area with a passenger.

I think I'm going to go for a full rebuild…bearings, seals, o-rings, cush drive, etc. If I'm going to do it I might as well *do* it! I also think a fork conversion where I can have a disc up front would be killer. I've decided since it's only a Sprint (that's already not fully original) to just make a bad ass scoot. Staying true to the original as much as I can, but not being afraid of performance upgrades.

Once I start the tear down I'll start a build thread and take a bunch of pics so hopefully y'all can help me tell what I've got.

Your wires look to be in good shape.

"If I were you"

Do a leak test.
On-the-cheap shopping list to start:
https://www.amazon.com/gp/product/B000RWB03W/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B01K7JFXAA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B002IZHF08/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Holds air?
Print out the wiring diagram and go through the bike with a multimeter.
Test the switch before ordering the vape. You could add that to your order, along with the correct air filter.

Ride it. You'll learn a lot by just puttering around.
Can you keep up with stop and go traffic? It'll be a little peppier with the vape.
Will it pull 2 up your hills?
Experience the Walk of Shame with a stock bike. A kitted bike fail is not as fun.

Learn-up!
You should be semi-fluent in Vespa-related German and Italian before you tear anything apart. Next baby step would be a clutch rebuild if it's still frustrating you, which you can do in-frame by removing the wheel and dropping the shock end.

^^^^ this.

I'm with Ray on this. Pressure test the crankcase, and go from there. Ride and learn while riding. A few hours with a multimeter pays big dividends in understanding the wiring.

Dialing in a scooter takes time and knowledge. And it only gets dialed.in when it's running and you can experiment and experience the scooter.

I'm excited for your adventure

That's for sure. Rebuilt my first engine and it was far from perfect. Wonky Stator plate and electrics were only resolved through longer rides and breaking down. Jetting has been as much about learning carburetor 101 as finding the right combo. Timings: learned how to measure them following recommendations but really understanding what the numbers mean will require lots of time on the butt dino. As it is now, it's not perfect but starts on the first kick, is fun to ride and gets me home again. I consider it a good start.

Bu…but…I wanna go stupid fast noooooow!

Thanks for the comments guys, I have officially slowed my roll, as they say. The new mantra is "one step at a time…*

New plan:

1. Build/buy compression tester. Ray, thanks for the head start.

***Assuming it passes or leaks can be easily fixed, then we'll do…***

2. Rebuild carb with new o-rings and gaskets (I'll have it off anyway for compression testing so might as well).

3. Order new jets and install, starting with Jack's recommendation.

4. Order new light/kill switch and see what we can get working, after continuity testing the wiring.

5. Order Vape and ask you guys a billion questions about installation. (I can solder. Kinda. Will need some refresher practice a bit.)

5. Ride.



*If case splitting becomes inevitable, OP can not legally be held responsible if go-fast bits are installed upon reassembly.

#5 if you do it, get a fresh harness and run it at the same time. no sense in trying to tie in to or hack what's there; especially when you don't know the condition of it.

but I'd chase the electrical for a bit before dropping that coin on a new EI kit.

leak testing is a great idea.

I'd use this as your immediate goal and try to knock out some of your bugs like the lights before you pull the motor and start taking stuff apart. You are getting good advice and I'll add a few things.

Get ray's list then you can pressure test so you know if you have a solid foundation.

You may as well check compression now too while it's easy - under 90 or 100 is cause for concern. I'd pop the head off just for fun to look in the cylinder and inspect for any signs of leakage at the head interface. Decoke head & piston as needed while you're in there.

Put in the proper jets as suggested. I'd pull the carb for a good cleaning now. How does it run? Go here if you need to: Mixture screw adjustment, got a good link?

About now I'd wanna check the ignition timing. If it looks good, it's now time for a butt dyno run.

Get after your clutch if you need to, is the inner cable frayed and catching somehow down at the business end?

Add a CHT gauge to your shopping list for cheap insurance.

I'd skip #4 & #5, may be unnecessary with all the rest for now.

You get the idea, now get on it, you ain't got much time!

^^^

very very solid advice. I'd take that route myself.

Yes, forgot that, duly noted! Unfortunately, I think I'm going to miss that goal. With Thanksgiving tomorrow and the parade on Sunday, I don't think I'll have the time or parts to get the bike in a good enough place to be a reliable enough runner for a parade. It's ok, we're going to shoot for a *really good* runner next year.

Today's question of the day is, where can I find a reliable source for torque values? I found this - https://beedspeed.com/pages/vespa-recommended-torque-settings - but will these be applicable to the Sprint? I have the Haynes blue book and even a lot of it's instructions are just "tighten this bolt"...

Thanks again everyone for being so welcoming and helpful. Excited to get it going! Hope everyone has a great Turkey Day!

not with that attitude you won't!

all kidding aside, if you're not all engines ahead full best to lay up and play it more at your speed.

but if you get a wild hair going, hit me up. I have all the clutch parts if you need 'em.

I don't quite have everything I need to do a proper leak down test just yet, but I did go by everyone's favorite discount tool shop and pick up their basic compression tester.

It's currently testing at 70 psi. (Cue sad trombone). When I did the test, I had the throttle wide open and kicked until the pressure gauge stopped increasing, which probably took 3 or 4 kicks but I gave it 10 for good measure. I also popped a little oil in the spark plug hole to see if that increased compression at all by helping to seal the rings. It made no difference. I also checked to make sure the head bolts were torqued to spec, which they were.

After the test, I put the plug back in and it started up on one kick, surprisingly. Idle seemed to be a little weak, but it would stay running and I putted up and down the street for a couple mins. I let it sit for about an hour and then I pulled the head to see what I could see. There is a little bit of scoring that I can see on the cylinder wall, but I'm not sure if that is more or less than normal. I can feel some of the grooves when I run my fingernail over them, however that circular groove just under the top of the cylinder is very smooth and I can't feel anything there.

Would love some expert opinions on what you see and what could be the cause of the low compression.




Can't tell if the bottom left there is dark because of a bad seal against the barrel or just water and gunk drains that way naturally...

Uno, due, tre!

what kind of compression tester?

it shouldn't start or even *TRY* and start at 70...

honestly for a old 3 port, with the carb and exhaust you've got that burn and barrel look fine.

Yeah I kinda thought starting should be harder/non-existent with compression that low too.

Tester is this bad boy - https://www.harborfreight.com/quick-connect-compression-tester-62622.html

The little time I had it here, the kickstarter resistance seemed 'normal' for an old 150, and it started pretty easy once it got used to fresh gas.

Yeah I agree, looks decent inside and I'm glad to see three ports in there too. Nice clean(synthetic 2T only) & clear burn pattern too. It looks like the head is sealing well. I'd be tempted to get a new set of rings and hone the barrel as long as you have it tore down this far. You can even do it without pulling motor out. How's the clutch behaving?

Thanks for looking, guys. After doing some additional reading about compression testing (https://www.klemmvintage.com/squish&comp.htm) I think maybe my compression tester isn't up to the task. I'm not quite ready to drop big coin on a quality one, so we'll just go with the fact that visually everything is looking pretty good. Below is a pic after I cleaned up the head and piston the best I could.

@Terry - Clutch was ok today for the couple mins I had it out. I've check the cable (decent shape still, not frayed or catching) and the actuation of the arm (with someone else pulling the lever) and that all seems ok. I'll see how it goes for a while but will eventually rebuild the clutch and install a new inner and outer cable. I still have to sort out the jetting and air cleaner once those parts arrive.

I bolted it all back up and I'm going to proceed with leak down test and timing...

I took the bike out today and it runs surprisingly great. I think adjusting the points made a big difference (they were barely coming apart before and I adjusted them to the middle of the range, 0.4mm) and I'm sure de-coking the head didn't hurt either. It started on one kick every time today, even after sitting for 20 mins or so.

Still need to sort the headlight out. I pulled the switch and headlight wiggled some wires but no go. I realized the horn works but only if the tail light switch is in the off position. I'll go through with a multimeter soon.

New question, I'm consistently getting a little bit of oil build up at the location in the picture below. That is left side rear floorboard. Slow leak in the oil tank you think? It's odd because the oil looks brown and not 2T green.

Could be 2t from the tank after oozing through crud in the tunnel. Have a peek inside. If it's leaking 2t it will be pooling inside a little.

Sounds like the electric on my bike too, but my lights only work when they are in the off position. Dunno why. All lights too. Tail light and brake and high and low beam. Beats me.

Pull the cover on your terminal box and trace the wire that goes to that added regulator, then compare your wiring to this. Regardless, you should find power w/ a multimeter somewhere on your switch that can be switched low , off or hi to your headlight, and provide switched power to rear running light per the diagram.

I have no idea how late Veloce stator mates up to earlier Sprint wiring harness, could be why the regulator was added? Anybody?


Courtesy of ScooterHelp

Yeah it gets a little confusing because my junction box only has 4 points where the wires come together and the diagrams I've seen have 5. I'm going to go through and make a "legend" of what wires come and go where and see if I can figure it out.

Again, those wires past the junction box look solid. Pull the flywheel and take a few more pics(?)

Looks from your pic like the double yellows from the stator are connected together to that regulator, then one yellow to the switch. Green is kill there.

Vape AC is 12v regulated single wire power and ground wire, which simplifies things quite a bit. You can seat the Vape regulator where your current one is.
Should you decide to go DC or variable in the future, you can change the regulator(for DC) or CDI(for variable ignition). The stator is the same.

My missing circlip to aid in pulling the flywheel is in the mail as I type so when I get it, I'll pop it in and pull the flywheel for some more pictures. I was thinking to pull the handle bar switch and try and clean the terminals and ends of the wires with some alcohol/contact cleaner to see if it's something simple.

if you don't have one, get a multimeter for troubleshooting electricals.

And do you understand how the "balanced AC" systems work? They use shorts to ground for circuits that are off. It's counter-intuitive, so make sure you understand that or you'll be "fixing" shorts, which is actually breaking the system.

I do have a multimeter I can use, yeah.

Honestly, the details of the electrical system are still very much a grey area to me. I try and follow wiring diagrams I've found, but what's actually going on with the bike seems a bit different. For instance, some one added a 6V regulator and I don't even understand the purpose of doing that when everything else seems stock. Was the bike not consistently putting out 6v at some point or is it band-aiding another issue? It also doesn't help that my understanding of electricity in general is rudimentary at best!

I think if I update the harness and ignition system down the road, struggling through that from scratch will help me to better understand it all.

In the old 'load balanced' systems with no regulator, they would start blowing all the other the bulbs if one should fail.

Because of this sometimes a regulator is added and this looks like it's wired like that w/ the yellow going forward your regulated 'hot' lead. Measure your voltage there.

And do we know your bulb is good?

My old post of Sprint engine restoration. Not sure if it helps.

engine porn - restore vintage vespa sprint 150 1968 engine


Harbor freight compression tester did the job

Can you add a pic of the inside of your brake light switch?

Ah, that makes sense. Ill try to get around to testing with the multimeter this weekend and let you know. Bulb appears good from what I can tell by looking at it. It worked for a couple days at first, but I'm not 100% sure it's still good. Maybe I can measure the voltage at the headlamp too to see if power is making it up there. Will post one tonight after work.

Good to know. How tight did you thread the tube into the spark plug hole? I just did hand tight because there's no real way to get a tool on there but maybe it wasn't tight enough…

Here you go, Ray.


What's this? An imposter!

I used the long tip plier to tight the tube. It has the rubber o-ring to help preventing leak.

Got it.
What you have there is a"closer/shutter" switch, so maybe more intuitive as you go through your wiring with a multimeter.
When you press the brake (and release the pin) it connects power to the light.

Oldie bikes used an "opener" system, that had the switch grounding the power to the bulb (kind of how the kill button grounds out power to the coil) until the pin was released by the pedal.

Looks to be in good shape with new wiring. That isn't bodgery there.

Sight glass crack/leak.

You can see the function of a closer here:

Thanks, Ray, appreciate the additional info. I will do some searching on the forum about how to properly use the multimeter to test power at the switch and the lights. Yep, figured this must be it. New sight glass and its associated accoutrements just arrived today. Figured when I have the carb off for a rebuild I'll pull the tank and fix that too. Also going to do new fuel/oil lines, add an oil line grommet in the frame (it's currently missing).

I made a thing. Been holding pressure for 24 hrs so I think it's ready for prime time! Just gotta make a plate to cover the intake then let the leak test begin.

Is it necessary to drain the gear oil before pressure testing the case?

I would say no.

Nope. Two totally different parts of the motor.