Inside a Carburetor

Smarter Every Day is a fantastic YouTube channel that really digs into explaining and simplifying how things work. The latest episode looks at carburetors, the device that mixes air and gas with the proper quantity and ratio to be compressed and detonated by the spark plug in the cylinder.

Even if you’ve been fiddling with scooter carburetors for years, you still might have no idea how they actually work. Like many people, you might understand the basic theory of a carburetor, but still feel like there’s a little bit of magic going on in there.

Destin explains the basic concept, then builds a clear model of a very basic carburetor, where you can actually watch the droplets of gasoline being sucked up from the float bowl, diffused in the venturi, and sucked past the throttle into the engine. Turns out it’s better than magic, it’s science magic!

Watch it now, the rest of this post is just my dumb comments…

As Destin’s dad points out, a real carburetor is much more complicated, with with different pathways and jets that can adjust the mixture and flow depending on how wide-open the throttle is. Removeable jets with larger or smaller holes allow further adjustment. And there are different shapes and sizes and designs of carburetors. But boy does this video make it clear how it all works. watching those tiny droplets of gas turned into mist by the suction nearly brought me to tears, especially knowing that a “real” carburetor would meter and disperse the droplets even more elegantly.

So why not just use a bigger jet (or a bigger carb) for more power? Early in the testing, Destin’s dad warns of backfire or damage to the engine if the throttle is too-wide-open. You can actually see backfire shooting out of the intake at the 18-minute mark, weird that they didn’t point it out! You can push the limits with tuning, but scooter engineers know what they’re doing, and your stock carb is designed for long, reliable engine life, maybe at the expense of a little power.

Every scooterist knows you can kill an engine by blocking the air intake. Towards the end, they’re having a harder and harder time killing the engine, because the holes where the choke lever was mounted are open. Enough air is coming through those tiny holes to keep the engine running. This is a reminder that the engine needs to be airtight and any tiny airleak in the carb, gaskets, manifolds, or seals will throw all this precise engineering out of whack. In some cases it can be fixed temporarily with more choke or a different jet, but ultimately airleaks need to be addressed properly for the scooter to really run properly.

Break Out the Spanners and Get to Work On That Carburettor

Haynes just released their Lambretta Repair Manual covering the series I, II, and III models from 1958 – 2000 including Servata and obviously SIL. The book comes in a nice hardcover with some color and plenty of black and white photos chronicling a complete tear down and rebuild. Who will be the first to put it to the test to see how accurate it is? Makes me wonder if the sales of Sticky’s manual had anything to do with the decision to finally release a Lambretta manual?

927.1442.600x400.5573

SIP to produce smallframe cases


Hodgespeed let us know that SIP is currently in the process of making tooling to produce Vespa smallframe PK-style engine cases. Great news in itself, as they’d gone out of production, but to me, the interesting part of the post is the CAD drawings of the mold for one side of the case. You hear a lot of people saying “Why don’t they just make….” Here’s the answer, look at the complexity and SIZE of that mold, and that’s just for one case-half (engine cases having two halves, you see.) So knowing that SIP has invested tens of thousands of Euros already, with all the machining and production costs to come, and testing, and the concern that the demand might be less than anticipated, or any tiny mistake in engineering or quality control could be disastrous, it’s a wonder they’ve taken on the project, though I’d wager most scooterists are certainly glad they did.

Now, a note, because everytime I post something like this, I get emails once a month forever from non-english speakers: 2strokebuzz does not sell this or any scooter parts. If you are interested in this product, please contact SIP in Germany.

#25 Factors Affecting Top Speed and Mileage

As with our last installment, I’m not addressing a specific question, but a lot of questions or conversations I’ve heard about motorcycle or scooter top speed and mileage:

Why do other scooterists report better mileage or a higher top speed than I seem to get from my scooter?

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That Petrol Emotion

We often have to make a big decision on whether or not to go with the ethanol gas offered at the pumps. Most of us aren’t too keen on the idea after hearing many warnings about how the ethanol will eat through your seals and gaskets on our vintage bikes and in many parts of the country you really don’t have much of a choice what fuels are offered to you. It’s a good thing that there is a website like Pure-Gas to help you find a station near you that serves up some ethanol free gas.

Check Engine?

Not quite scooter-related, and maybe a little crazy, but ultimately, a worthy quest: Check out Jalopnik’s campaign to ban the confusing “Check Engine” light and replace it with useful onboard diagnostics.

Libertarians, complain away, but it doesn’t make sense to have a computer, a million sensors and a text display (if not a video display) in your car, then hide the results from the consumer.

If you’ve ever paid a mechanic $90 to tell you that your gas cap wasn’t screwed in tightly enough, sign the petition before February 16.

Instant Club Hit

Who knew the Clubman exhaust was 30 years old? or who really cared? Well Mark Broadhust apparently does and has devoted a lot of time and energy into the exhaust. It’s no secret that Mark and his company MBDevelopments have come up with many quality performance parts for the Lambretta over the years but man, talk about information overload! Check out this dyno chart and picture filled facebook post of the history of the exhaust, how he has gone about improving them, and a sneak peak at a new version being made in collaboration with Scooter Center Koln.

Future Of The Past

Is a new slogan for Giannelli exhausts, or maybe just a poor google translation. The company is reintroducing many of its pipes for mopeds and scooters from 1980’s on the angle that if it was good enough 25 years ago it’s good enough for old guys with more money to relive their youth with now. Also appears the company will introduce a new exhaust for the 4-stroke LML Stella/Star. Living in the past not for you? Well then maybe the MyMuffler program from Polini is more your style. I’m sure you often thought “boy would I like my name emblazoned on the can of my exhaust” well now you can!

2011 Gas-Price Scooter Frenzy Begins

POCPhil launches the 2011 gas price scooter media blitz. Fine, even Phil’s doing it*, I’m not gonna begrudge dealers for milking the gas mileage argument, scooter shops that lasted through 2010 really need the business, and I hope 2011 rivals 2008 for scooter sales. But if consumers do some research, they’ll see fuel prices are an excuse to buy a scooter, not a true justification.
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Book Review:
Vespa Scooters Essential Buyer’s Guide

Veloce Books is a British publisher focused mostly on vintage cars and motorcycles. They’ve released several scooter books, some reviewed here in the past, and all worth checking out. Their newest scooter-related endeavor is The Essential Buyer’s Guide: Vespa Scooters (subtitled “Classic two-stroke models 1960 to 2008“) by Mark Paxton. The word “Essential” in the title is not hyperbole, this book is truly a “must-own” for anyone considering the purchase of a vintage Vespa.
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Vespa Scooters Essential Buyer’s Guide”