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Wooaah, it’s been a while I know but we haven’t forgotten you. If you’ve missed any episodes then you can either Google ‘SLUK Superlui’ or start here.

In our last episode, Sam powder-coated his Lambretta chassis with the help of Gibbo from Nuneaton Alloy Wheels and Powdercoating. Then it was time to put the “blue beast” together and see how it worked as an ensemble.

As ever, these things never go smoothly, so here’s a short list of issues that we had to overcome.

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Hoovering sand out of the fuel tank; not totally successfully
Hoovering sand out of the fuel tank; not totally successfully

#1 – Tank trauma

If you’ve bought any cylinder kit from a tuner in the recent past then you will no doubt have encountered strenuously imparted advice about not using certain stainless steel, rusty, blasted or powder-coated tanks. Any of these contaminants that work their way to the carburettor can block a jet, causing lean fuelling and potentially a seizure or a holed piston.

The reason that stainless steel and blasted tanks are particularly despised by experienced dealers is not only for blocking jets, but because the metal polish and grits used in blasting are all abrasives and if they wash through to an engine then they can wear out the bore, rings or crankshaft bearings in no time. Imagine sex with sand as a lubricant and you get the picture.

So, that being the case, don’t ever do what we did.

If you ever buy a used fuel tank from a powder-coater and they offer to blast it inside and out, for heaven’s sake, remember Amy Winehouse’s reaction to rehab.

Just say ‘NO, NO, NO’.

That is the amount of sand we managed to wash out of the blasted fuel tank on one attempt. There were many subsequent attempts too
That is the amount of sand we managed to wash out of the blasted fuel tank on one attempt. There were many subsequent attempts too

In fairness, it should be possible to clean out a normal fuel tank quite easily, but there’s nothing normal about Vega tanks. There’s a deep tube inside the neck of the tank which means you can’t see inside, and only a 10mm exit hole for the fuel tap.

To cut a long story short, after getting the freshly-blasted tank powder coated it took several weeks of trying different methods to hoover, jet-wash, suck and remove all of the blasting media.

I set up a looped system with a Facet solenoid fuel-pump drawing from the tap hole, through a paper fuel filter and circuiting the ‘cleaned’ fuel back into the tank. There was so much grit inside that it clogged up three fuel filters before eventually killing the fuel pump.

Dyson with death

I tried sucking the grit out with a vacuum, even going to the trouble to 3D print the correct size adapter nozzle to connect Tracy’s Dyson to the tank. Not only did it fail to work brilliantly but I wasn’t very popular with the lady of the house either.

In the end we resorted to putting in half a litre of petrol, sloshing it around with a finger over the drain hole, filtering the fuel and doing it again.

Depressingly, every time we did it, out would come more blast grit.

After at least 50 attempts to clean the tank, with the petrol finally coming through pretty clean, we relented, cleaned it with Oxalic acid and fitted it to the scooter, but still with a fuel filter in-line.

We could have saved days of work if I’d simply said NO, NO, NO… My fault…

Home-made LED Light-boards for the original rear light seemed like a good idea
Home-made LED Light-boards for the original rear light seemed like a good idea

I tried to be clever with the rear light by making an LED board filled with ultra-bright COB (Chip On Board) LEDS. The series of LEDS worked for a period of time at the required voltage but eventually one would overheat and fail. No matter what combinations I tried I could never get them reliable enough to run for more than an hour or so.

Admitting another failure I hunted out some 12V LED panels and fitted two of these inside the tiny, plastic Lui rear light unit. These work perfectly on the DC stator and regulator conversion that we carried out here.

A stack of dedicated 12V LED COB boards was a much easier solution
A stack of dedicated 12V LED COB boards was a much easier solution
A bright rear light, even off a normal 12V AC Vespa electrical system
A bright rear light, even off a normal 12V AC Vespa electrical system

#3 Exhaustive experimentation

You may remember from episode 7 when we first ran the engine on the dyno that we had a target power output of 12hp for the modified Pinasco engine, which we exceeded on the very first run.

What became very clear from that dyno test was that the short Ludwig & Scherer exhaust designed for high-revving kits was unsuited to the moderate port timings that we’d picked for this engine. What we really needed was a longer exhaust offering better bottom end power. The only thing we had to try was the Ludwig and Scherer ‘Franz’ pipe that works so brilliantly on Underdog; the Quattrini SS90 that Team SLUK used to win the Road class of the Tside 6-hour scooter endurance race.

The Franz worked ok, shifting power down the rev range, but it didn’t rev on too well on this engine. What we really needed was the first Ludwig & Scherer exhaust but with a longer tuned length to make it work better at lower revs.

L&S’s cone-formed expansion chambers are fully-tapered from the port so a better way to extend the tuned length would be to cut out one of the sections and roll a new cone with the same entry and exit dimensions but tapering over a longer length. That’s beyond my skill level.

50mm of additional tubing added to the downpipe
50mm of additional tubing added to the downpipe

Instead we elected to cut the downpipe and weld-in a piece of straight stainless steel tube. As an experiment, we tried a 50mm longer section. It actually worked ok, bringing power down the rev range and increasing torque.

Given the positive results the next solution was to cut the tube and weld in an overlapping piece of stainless tubing that would allow us to try lengths from 50mm to 100mm longer.

100mm of extra length added to the downpipe
100mm of extra length added to the downpipe

The engine clearly liked the 100mm longer downpipe as power picked up once more to 13.7hp at 7,780rpm. These are quite moderate revs for a smallframe motor and hopefully that would be enough power to give the SuperLui a top speed of over 70mph while still remaining reliable and economical to run. That was always our objective.

The one downside of extending the exhaust is that it now stuck a full 10 centimetres further out the side of the scooter than before. Thankfully the engine is in a Lui because it wouldn’t fit under the panels of a Smallframe Vespa any more.

The exhaust hangs out the side quite a way, but aesthetically it balances the offset Vespa engine
The exhaust hangs out the side quite a way, but aesthetically it balances the offset Vespa engine

Aside from looking a little unusual the only downside to the extended exhaust was the worry that it might snap since so much weight now hangs on a longer downpipe. Nevertheless, Sam made a new exhaust bracket to connect it to the engine and it all seemed to line-up fine. Fingers crossed…

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Four different stages of the SuperLui project.

  • Pink shows the engine with a standard PK exhaust – pretty poor.
  • Blue is the engine when we first dyno tested it with the Ludwig and Scherer exhaust.
  • Yellow is the same exhaust with 70mm added.
  • Green is the same exhaust with 100mm added.

The graphs are shown against speed in 3rd gear.

Yes these are spark-proof welding shorts, in case you were worried
Yes these are spark-proof welding shorts, in case you were worried

#4 Lost SIP wheel nuts

 

I love SIP tubeless Vespa and Lambretta wheels. Fitting a SIP Vespa rim to the rear of the SuperLui seemed sensible, but what happens when you’ve mislaid the nuts that came with it and normal nuts don’t fit? Well in that case you can make some from M8 thread connector nuts (cylinder head cowling ‘long’ nuts) from Screwfix machined in a lathe.

What do you mean you don’t have a lathe. Nor do we, but we do have a grinder and an electric drill. With the nut mounted on an old bolt in the drill and the grinder running on it we have an easy lathe, sort of.

Don’t say that you can’t learn anything from Russian hillbilly engineering videos on Youtube. Just don’t copy Russian driving skills, that’s all I’m saying.

3D-printed bracket allows the original Lui switch to fit onto studs and long nuts fitted to the master cylinder bracket
3D-printed bracket allows the original Lui switch to fit onto studs and long nuts fitted to the master cylinder bracket

#5 Light switch mounting

 

Anyone who has ridden a Lambretta Luna will no doubt be aware that they were fitted with a smart-looking but totally wanky helical throttle control. This seems to have been binned-off on many original bikes in favour of some sort of motorcycle throttle.

For the SuperLui not only did it come with a bike throttle, but we also needed to find space on the space-age handlebars for a throttle, but also a hydraulic master cylinder to power the disc brake on the Honda Bali forks.

These changes meant that we completely ran out of space for the original light switch unless we found a fancy way to mount it.

With a 3D printer it really isn’t hard to make not only models of parts that you want to make, but in the case of something like this that won’t be subject to a lot of stress, you can actually design and print a functional part in a few hours.

For those of you who’ve not yet discovered the joys of 3D printing, let me explain the process:

  1. Take some measurements for the part that you want to design.
  2. Draw it in a 3D design software such as Creo or Designspark Mechanical
  3. Transfer the drawing file (STL) to a ‘slicer’ software program that converts the solid shape into a 3D-printable file
  4. Print it on a 3D printer (decent ones cost less than £200 now)
  5. Test fit it. If it fits go to #6. If it doesn’t fit return to #2.
  6. Celebrate a job well done.

It is possible to print hollow objects which have a honeycomb centre. These are quicker to print and use up less plastic but they are also correspondingly weaker. For an object like this you can choose to print the part in solid plastic for maximum strength.

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#6 Solving the badge crisis

While we were busy on the printer we elected to save money on buying original-style badges (Casa Lambretta make decent replicas) and instead design some specific ones. In place of the large Lui badge on the legshields I made one that reads ‘Super Lui’. This isn’t as easy as it looks because the legshields are double convex. We also made a similar one to blank the speedo hole in the headset because there is now a GPS speedo mounted to the legshield toolbox.

In place of the ‘Innocenti’ badge at the top of the legshields we made one that said ‘Guilty’ because in some eyes we are, at least of corrupting Innocenti’s original design.

Both badges were printed in blue PLA plastic, sprayed matt black and the paint rubbed off the high points on the badge while still wet to reveal the blue letters. We then stuck them on with 3M badge tape.

Words & images: Sticky

Next time: In the last part of the SuperLui saga we’ll show you the finished article and explain how it fared on its first two rallies and in its first crash…

Are you and your scooter rally ready? The SLUK Shop is full of stuff a road-going scooter rider needs

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