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.