Modern Vespa

And here John was telling me to calm it down!

Not that you don't make an excellent point, Jack. Maybe I'll do a Frankenbuild of my old Malossi 166 that way. I'd have to either buy a new crank or replace the conn rod, which would be a new one for me, but it'd be a good excuse to buy a cheap hydraulic press...

(And this, PlantGuy, is how we wind up with all the crazy builds we wind up with...)

Another real-world testing vote - thank you! I already have the side-stand so clearance shouldn't be an issue I've already got the frame wired for the P200 / Ducati CDI off of the P motor - thinking about just swapping that over. I was also looking at these as alternatives:

VMC - https://www.scooter-center.com/en/ignition-vmc-cnc-vespa-px-cnc-rotor-incl.-voltage-regulator-vmc1018

SIP Sport if I want to get spendy. Appreciate the shared experience to prevent more pain I am looking forward to a little grinding / tuning, but not going whole hog just yet.

For exhaust, it sounds like Pollini or potentially Malossi. I do have a new Sito + that came with P motor that I may start with.

Interesting and good to know! If you were buying an "expenses-spared" build, is there a cylinder kit that you'd choose?

Also, side note - is 20hp doable on the existing 3 speed gearing or would I need to plan on an full internals upgrade?

Gearing doesn't make the 20hp happen, it makes it usable.

If your 20HP curve is peaky, 3 speeds will be torture. If you have a flat torque curve, it might work. If your roads are hilly, 3 speeds are likely to be torture. For a 3 speed build, you should build a motor with a broad flat torque curve, not a peaky power curve. I have a 3 speed motor sitting for a future project but I also have sourced 4 speed internals. I'm not sure which way I'll go but I have options.

That is one of the things I have admired as I go back through the history here!

As an aside, I have a TIG welder that I primarily use for aluminum welding. Adding a 3rd port looks to be fairly straightforward

On this note - where do you all get your custom sized packers / cylinder head gaskets to optimise the tuning? I noticed a few available from SIP / SC but the sizes seem pretty broad.

https://www.sip-scootershop.com/en/product/racing-cylinder-vmc-crono-187-cc_84140500

Not over cheap but this would work with a 3 speed. But only if welding the 3rd port.

https://www.sip-scootershop.com/en/product/racing-cylinder-vmc-stelvio-177-cc_84140100
This kit if going with the thick base packer.

Definitely don't want torture, Touring power is the goal!

I've been playing with the gearing options & 3 vs 4 speed - what do you think will push you to do the 4 speed upgrade?

Thanks Jack, I was looking hard at the VMCs already!

The gaps are so big that getting it right for uphill at 45MPH is hard. If you miss the power band in your guesswork, that same hill is like 30MPH in 2nd. I did some simulation work but I seem to have misplaced it. Let's not kid ourselves, I have the parts so there is almost no chance I will build it as a 3 speed unless I'm doing some period correct build, and I just don't see that happening.

Hills are a big thing here in San Diego. There are several large ones on my way to/from work, and running up them at 45MPH is pretty much my litmus test for "yeah, I can ride that" vs "hell no that sucks".

I have yet to try one of the VMC's, but they get consistently high marks around here, so you won't go wrong with one.

Personally, I have a long track record with the BGM 177 and am a big fan of it. Its ports are nearly a perfect match to a Polini 177 once you cut the gates out, so I use Polini spacers, which you can get in pretty much any thickness you might desire.

And because the head is inset, you can easily dial in the squish to within 0.1mm of your target.

Almost the same price as the VMC's, too.

Others have already covered the gearing challenges of the three speed, so I'll skip those. I seriously doubt you'll see 20 HP out of this motor, regardless of what tricks you play in the build, though. Expect 15 and you'll be happy if you get more.

This makes sense - also gives me more comfort in keeping the 3 speed for this one. There are hills here, but you have to go looking for them Honestly more than enough for this build - I have to keep reminding myself that this build won't be a screamer. I'm saving that for the next one

Ok, upon further reflection - If I do a long-stroke, long rod crank and plan on using a thick packer this would help on the torque side right? Is there a downside for doing this with any 177 cylinder?

Also, if we are looking at a 187 / 190 build - would a 20/20 carb still be correct? At what point does the carb need to be sized up?

If you already have the 20/20, I'd start with that.

Depending on where you wind up, it *may* make sense to upgrade, but it'll depend on how much mix you actually get through the boost port.

If the motor seems like it's struggling to breathe at high RPM's with the 20/20, then you can think about an upgrade.

Really, though, you should recognize that you're going pushing limits that could be avoided entirely by just buying a four-speed three port motor and running that. You're clearly going to wind up at that point sooner than later, so rather than going wild on this one, focus on learning the building skills so you'll get it right on the second one.

Makes sense and I look forward to figuring out the limits

My dilemma is that I have a stock 20/17 & a 24/24 autolube. I can convert the 24 to non-autolube for this or I need to source a 20/20.

Anyone have an extra 20/20 kicking around that I can trade for some $$? I'd prefer not to give SIP any more of my money than necessary Or is there a way to modify a 20/17 to make it flow more? Would that be worth the effort?

I have a 20/20 or two floating around, I think. Lemme check the workshop.

Since you already have the 24/24, you could start with it, though. If you can't get the 1/4 throttle to dial in, you'll know what you need to do.

Also, check out the domestic options. Scooter-Speed and Scooterwest are both excellent, as is my beloved ScooterMercato, it's just on the wrong side of the country for you.

You don't *need* to do anything to use an autolube carb non-autolube, so long as the airbox and gasket are not for autolube. The passage will be blocked by the gasket.

Much appreciated CM! Sounds like a good fall-back plan of using the 24 as-is with a new gasket and watching for known downfalls.

I'd love to use anyone else, but between stocking issues and shipping speed it seems to be easier to order from one of the German behemoths even if their CS is lacking

I agree with Chandler over carburation causes issues on these just like a full size car. if you ride normally even with a 20/20 you will be cruising around at 1/4 - 1/2 throttle. You'll be tuning for partial throttle already. Going with a 24/24 or 40% larger bore carburetor means your tuning for an even smaller throttle opening. Unless you plan on running WOT a lot make your tuning life easier.