Modern Vespa

I have a 150 cc reed valve Stella LML engine that I am rebuilding with a DR 177 7 port cylinder, 24/24 SI carb with Polini Venturi and a SIP Road 2.0 exhaust.

From what I understand, I need to upjet and advance the timing.

I don't know where to start, however. Is there a tuning spreadsheet of various set ups for Vespa and LML engines? or, a place you can direct me to find the answers.

I've built 2 stroke kart engines and moped (Garelli) engines in the past. Just at a loss for where to get the information on my build.

Any help is much appreciated.

Thanks!

Drop the 80's technology DR cylinder and use a modern cylinder such as a BGM 177, or otherwise.

There is a lot to unpack with your request/build.

More importantly, what are you trying to achieve?

I know there's plenty of options out there for cylinder and carb and pipe... etc.

I have a 1974 Vespa Rally 180. Looking to ride it with a little more power and some reliability. I know to be careful not to lean out this thin DR cylinder...

I developed an air leak (internal seal) in the stock lml engine. Decided to rebuild it with cylinder, car and exhaust that I'd bought over the years.

If you already have it, the DR is decent enough and will serve you well, if you're just after a useful boost to an otherwise stock motor. It may be a cylinder developed in the 80's, but your motor hasn't changed much since the 60's

Just run it at 18 degrees timing and use something like a 112 main jet. I ran one with a venturi and used a 120/BE5/122 main stack and 52/140 idle. It was most enjoyable compared to the stock 150 that it once was.

swa45,

That's helpful, thanks.

Did you run a 24/24 si? What exhaust?

Yes, a 'faster flow' 24/24 ie. the passage from float chamber to main stack was drilled larger to ~2.2mm, hence the 'optimised' main stack. I had a BGM BigBox Touring on that one, and for reference a VMC Stelvio head, as the squish on a DR177 is excessive. It was honestly one of my favourite all round setups and I preferred it to the previous BGM177 for daily, local riding. Sold the scooter three weeks ago.

Once again I am in full agreement that there are more powerful (and more expensive) kits available, but if you already have the DR, it will give you a decent bang for your buck.

I also have the faster flow tap and carburetor... Mazzuchelli crankshaft... carbon fiber reeds.

Thanks again.

Since you already have the DR, why not give it a try? You can always go with a more modern kit later on. The DR is basically a stock cylinder with larger displacement. I think it might be easier to set up, especially with the restrictive Stella reed valve.

I have read of a number of successful builds using the BGM 177 kit.

Yeah, I know I'm late to the thread, which makes me hate to say this even more, but I think you're going to be disappointed and wish you'd consulted us before you dropped a stack of cash.

While the crank, new reeds, etc. are sunk cost at this point, they're basically wasted on the DR. You'll get 12 HP, 15 absolute max if the new crank is a flowed long stroke and you set it up correctly. Even then, you're limited to ~8k RPM's by the 2mm rings, which in turn means you're hitting the wall of physics before you can get into a serious power band.

Is it better than stock? Sure, but in terms of value-for-money, it's not good by today's standards.

Your best bet at this point would be to sell the DR, especially if it's still New In Box, then use the proceeds plus a couple hundred bucks more and buy a BGM or VMC 177. Either of those will bolt on with the bits you already bought and get you into the 16-18 HP range.

Also, the 24/24 is too large for the DR on a 57mm crank. You'll struggle to tune it at 1/8-1/2 throttle because it's not drawing enough air in that range.

If you're not on a long stroke, go back to the 20/20. It'll run better than the too-large carb and since you can't get enough rev's for it to matter, it won't really help you at WOT, either.

When you build this, make sure you focus on the basics: airtight motor, squish, port and ignition timing.

The higher the state of tune, the more important it is to get those right or you'll have the chance to get it right again after it blows up and the replacement parts arrive.

Now that I've said my piece, I mostly agree with swa45 on the timing & jetting:
-18 BTDC, maybe 17 if it runs warm, set at 4,000 RPM's
- 52/140 idle

If you're on a 60mm crank, use a 1mm base gasket and whatever head spacer gets you to a squish of 1.2mm. The head height on DR's used to be pretty random, so you'll need to measure and modify accordingly.

I'd go 140/BE5/118 for the main stack, though. You're already going to be struggling to atomize at lower throttle positions with the 24/24 and the 120 AC will make that even worse.

Thanks for chiming in Chandlerman... all info is being digested.

I have a p125x case I was planning on building after this one. Any suggestions on this one?

Anything from 'don't bother' to 20hp... ?

A DR cylinder would be something that would enable me to get home if nothing else is available; wouldn't be anything i would use to build a planned engine. We can talk about all the modern things going on with that cylinder, but the biggest point is it's not much more money for that cylinder that makes it a no-brainer. If you are going to do something, do it right.

That's part of what I love about tuning these motors; you can build anything from "don't bother" to more than 20 hp. It's all a matter of time/effort, money, complexity, and expertise.

The key is to know what riding experience you're wanting, and we can design a build that matches those requirements to the extent that the various engineering triangles allow ("good, fast, cheap: pick two," and various other sets of tradeoffs).

For a serious rotary build, you're going to be optimizing both intake and port timings. If you want to go reed, you can get 25-30 HP off a small block (125/150 cases), but that's going to be a lot trickier project and I would not recommend it to start.

Also, in case it wasn't already mentioned, more HP also means more frequent maintenance and more chances for catastrophic failure. Even tuning parts are may not be up to the task when you get into serious motors, and they rarely fail without taking something else with them.

Which is not to say don't do it--I freakin' love building and riding stupid-fast scoots. I just don't want anyone to get into it, regret it, and then leave the vintage scooter community entirely.

Get one build under your belt, then you can take what you learned and grow from there.

Oh, and as soon as you get a fast motor, you're going to start needing to upgrade all the other moving bits, too, like tires, shocks, and motor mounts, and that stuff adds up FAST.

And a front disc brake.😉

Meh. Stopping is overrated.

Not to hijak the thread, but everyone always talks about reliability and performance, but for fun, what would you guys do to a stock stella motor to make it "unreliably" fast?

Funny you should ask. We just had this conversation over in one of my build threads after the top end and crank died on my LML motor...

- Quattrini M1XL top end
- P200 60mm bell crank
- MotoTassinari Vforce4 reeds in an MMW block.
- PWK 34 carb
- SIP Nordspeed exhaust (Lotta good exhaust options, though. Pick one to suit your taste)
- SIP Vape variable timing ignition
- P200 primary/gearing
- Upgraded clutch

That'll give you something that's dangerously fast (~30HP) and will run faster than you probably want to go on 10" wheels.

Yes... enjoy stopping, too. Definitely need a disc front brake setup.

Currently, I do not touch the front brake. I much rather slide on a locked rear than dip and dive!

You have told us a little about your motor, but what frame is it going into? That'll help with questions like disc brake or anti-dive options.

Frame is a

Rally 180.

We all love a good Rally. Post up some pictures when you get a chance.

Okay, I'm back in country - back to ATL.

Got the LML back together and running on the Rally. Have had a few runs for a total of about 1 hour that was fun and long awaited! But...

Multiple plug readings (color) look good - beigy. I'm a bit confused, however. I have similar color with very different Main Jets and cannot seem to get the engine to 4-stroke at full throttle (Main Jets from 118 to 140). Won't 4 stroke on the stand or on the road. It just revs out.

It idles fine (no matter the main jet).

It does 4 stroke with less throttle input, I'd say 1/8 to 1/2. It is a bit rough. When I get past 1/2 it revs out.

Reminder: DR 177 Kit (3 port matched, including cylinder skirt) on an LML150. Carbon fiber reeds. SIP 2 exhaust. Mazzuchelli crank. SIP Cosa 2 clutch. 24mm carb (52/140 idle // 140/ BE5 / 118-140), carb DRT modified, Polini venturi and fast flow fuel tap. Timing 18 degrees.

Started with Chandlerman's recommended starting point for jets as per above: idle and main stack. I could not get it to 4 stroke on the stand. Also, attempted to follow - Guide: SI Jetting Chart + How to Tune an SI Carb - by Chandlerman, but got hung up at finding a jet that would not let me rev out.

Any assistance appreciated.

Thanks.

Have you drilled the hole/passage to the jet gallery in the float bowl? The restriction in the fuel passage may not provide enough fuel for the larger main jets. It is common to enlarge the passage 2-2.5mm on tuned engines.

Hibbert... thanks.

yes it has been drilled, that's what the DRT modification is.

This is what I was going to ask. If it hasn't been drilled, then the float passage will prevent the main jet from being effective about about 120-125, which is probably not enough even for a DR.

If you want to know more, I did a whole video on si carb fuel starvation:

Did you measure it? The one in my video was a Worb5 that has supposedly been drilled before I bought it, too.

If you're sure the passage is drilled, you can further test by running the motor with the jet stacks exposed and loosening the main jet while it's running. That allows fuel to bypass the main and *should* let you confirm that you're not rich enough.

And if you can post a video of the motor running and revving, throttle blips, etc. then that also helps with diagnosis.

Awesome Chandlerman.

I'm on it. I'll let you know what I come up with.

It might be a good idea to verify the fuel flow to the carb and rule out any issues with the fuel tap and supply. Also verify the hole size on the float passage. If you have some drill bits 2.0-3.0mm you could use those as a gauge. Might try a 120 air corrector on the main jet stack to get a richer mixture. Might try running with out the vortex to see if you can get it to sputter. I like to keep notes and make changes incrementally. I'm easily confused and my notes have helped me stay organized. I've got 18 pages on my 190 carb tuning it was very challenging and very rewarding.

Thanks Hibbert.

Fuel flow was an issue... but for another reason. Had some fuel in the airbox. Blew it you with compressed air. Out flies the round gasket from the tap into the carburetor float bowl. It was missing and leaking so slightly. So that made if more difficult to find the rich jet. Replaced it.

I'm also checking torque on the sleeve bolts regularly after runs and engine cool down. The one in the middle is not staying torqued. Need to fix that to eliminate any air leak influence.

More, later today.

Unreliablly fast you ask?…Install a ported DR177 kit with a Mazzy crank, then not upgrading the clutch and have the carb jetting set up two points too lean.

The two ways to make any motor unreliable are by cheaping out on parts, in particular using things that are under-spec'ed for the build, and cutting corners on your workmanship, which could be any of not doing proper dry-fitting and measurement, pressure testing, following proper build methods, etc.

Past that, if you build a solid motor, you need to realize that it's about how much ongoing maintenance the motor is going to require to *keep* it reliable.

I have multiple 25-35 HP motors which are one or two kick starts, maybe three kicks if they've been sitting for a few weeks. They are full of very expensive parts and tend to need significant maintenance, often the result of surprises about how under-capable even "performance" parts are (Mazzi cranks, I'm lookin' at you).

Finally, it's pretty rare that a motor will go from Just Fine to Dead. Ignoring symptoms is a great way to achieve unreliability. Air leaks are the poster child for this one, followed by rough shifting/slamming into gear/etc that are your cruciform/gearbox/clutch crying for help.

Interesting points. I wouldn't consider crank failure to be a maintenance item unless it was due to overly high mileage. Failure because its limits were exceeded is a different matter.

I would definitely put checking and addressing air leaks on the list.Tuned engines are definitely more likely to be damaged by minor air leaks. I also think that more extreme heat cycles would make them more likely to occur.

Accelerated parts wear would also be part of it.

Would say that a higher revving engine is more likely to get damaged by sloppy shifting, so frequent adjustment and lubrication of cables would be on the list.

There are also a bunch or little things that can wreak havoc if they get loose.

The other thing that I've never seen mentioned plainly about Vespas is that a catastrophic engine failure can mean the scooter locking up at speed. The shitting your pants factor increases with higher revs and speed.

Haha I meant performance wise. Everyone wants performance AND reliability. I was just curious about straight performance. Im well aware maintenance and riding style are prominent factors in reliability, just curious what people would do to a stella motor for "shit yourself fast" at the expense of any sort of reliability.

The build for straight up performance would most likely start out the same as it would for reliable performance, you'd then go wild on the port timing and size pushing the power band up the rpm range.

The mechanics of turning a shopping bike into something potentially much more dangerous is almost the least difficult bit.
Set up skill and adjustment, is where the power and relative reliability comes from. And the higher the performance the more challenging (usually expensive) it gets. Anyone who tells you it's easy doesn't have a clue!

First thing to remember is that there's nothing slower than a non-running bike. I (and, I think, most other serious builders on here) aren't going to let that caveat go.

If you want REALLY REALLY fast, sell the largeframe and buy a Smallframe. build a Quattrini M200S, which also requires Quattrini cases, crank, and exhaust. Spend another $2k on gears, clutch, carb, VForce reed, etc. and you have a 100+MPH bike that puts out 44 HP at peak and all you have to do it not screw up the build.

If that seems a little wild, Quattrini also make the M1L60S. You can fit it to stock Smallframe cases if you don't mind doing some machining and get 33-35 HP and, again, go over 100 MPH if that's your jam.

Either of those motors are more power than you really want for riding around on the streets. They're loud AF to the point you want earplugs when riding them and you'll feel like an asshole riding them around town after a while. Plus, they have a bad tendency to try and wheelie up and over on top of you when you hit the power band if you're not careful or not experienced with motors like that.

BUT... assume we're starting from Stella cases, so naturally reeded 150cc.

I'm going to number this list for ease of reference and so people can chime in as "On #1..." rather than giant quote-posts.

1) 60mm crank. It's longer than stock, gives you an extra 11cc's, but not so much that it starts to create too much mass via the rod. It's also essential when it comes time to work on your port timings without needing a machine shop to start decking parts. If you want wide power band and torque, especially at lower RPM's, get a bell crank to increase crankcase volume. If you're just chasing peak HP in a narrow power band (which is for racers and, honestly, chumps), get a full circle or at least flowed crank.

2) Serious reed block & reeds. I run an MRP block with Moto Tassarini VForce4 reeds. You can choose another block, but the VForce4 is, undisputed, the best reed.

3) 34mm Side draft carb. Pick whichever flavor you're comfortable with. I like Keihin PWK's. Extremely tunable across throttle positions.

4) Vape Sport (variable) ignition. I recently tested variable vs. static on my Lambretta and got an extra 1.5 HP on the ramp of the power curve just making that change.

5) For exhaust, any of the SIP Nordspeed tuned pipes are good options at this point.

6) Top end. We are in a golden age of cylinders right now, to the point that I don't know that I would pick just one.

Neither of my last two builds have been Largeframes, but they have been Quattrini (M1L60S & TV210), as will my next (Quattrini M1XL if SIP and US Customs can ever get over their bitch fight). That'll be direct intake and should produce over 30 HP, ideally something between my Lammy and the Smallie. And quieter than the Smallie, too.

If you want case-inducted, the Quattrini M1X, Malossi 177 MHR, Parmakit, VMC, and BGM are ALL excellent kits. The VMC & BGM are a lower price point, but at this point in the budget, the difference is practically a rounding error.

7) clutch -- You can probably get away with the SIP Supersport (motorcycle/smallie style) clutch. It's allegedly good up to 30 HP. Past that, it gets expensive fast.

7.1) Get a pinion gear clutch arm & plunger. It's a significantly better design and massively lightens the clutch compared to the standard lever arm, but not full-on hydraulic clutch crazy.

8) Gears. Assume you're going to want to run 23/65 clutch/primary gearing, so you're going to need a new primary drive gear or just buy a whole new Xmas tree. Crimaz or other super-hard cruciform. And eventually, you're going to want to change up your gear stack, but you can't do that until you have some actual data on motor performance, but figure another $500 or so worth of loose gears as you work out exact gear ratios.

That's all just a parts inventory with minimal rationale.

Putting it all together is where the magic happens. Depending on who's doing the work and the trade-offs you make in the setup, the result of all that will be anywhere from 15HP all the way up to 30+, especially if you're willing to give up a little bit at the peak to widen the power band.

And NONE of that has to be unreliable. Especially if you're willing to forgo "cheap" in the name of "good" and "fast."

It just may need serious attention every thousand miles or less, depending on how you ride it, but that's the price of admission to the big tuning game.

7.1 is something I hadn't come across before, I did some searches and is this what you mean?
https://www.vespajets.com/product/crimaz-vespa-clutch-pressure-plunger-toothed-125-vna-ts-150-vba-super-px-t5/

I was considering this setup
https://www.vespajets.com/product/pressure-plate-clutch-sip-xt2000-2-0-for-vespa-125-vna-ts-150-vba-super-px-t5/

Yup. That's the one. I have this pressure plate, and they also make one that's just flat with no plunger.

People love or hate them, because when they work well, they're nice, but they also have a tendency to eat themselves and dump ball bearings all over your crankcase if your clutch cover is not on square.

I don't like the sound of that, I think I'll go with the geared one, I've got a Yamaha with a similar mechanism.

Anyway sorry for the thread highjack.

My tuned engine building experience was long and frustrating, but is finally paying off. There's nothing like flying down the road with an engine that was sitting in bits on the bench not so long ago. That NEVER gets old for me.

Also, once you go fast, it is hard to go slow again.

If I was doing this build all over again, I would have started by replacing the Stella reed block with something less restrictive.

this is the exact write up i was hoping for. I'd say about 60% of that was what I already had in mind, the rest is very informative. This will be my winter project, so we will see how it turns out. It will be more track oriented, not top speed, so I'll have to figure out gearing for that.