Modern Vespa

A big thank you to all the folks who have posted on MV about how to install a Big Bore Kit (BBK) on a LX 50. Thank you to Scooter West for the great instructional video

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And big thank you to Scooterpartsco Motovista for selling me the RMS Big Bore Kit and giving me some good advice.

I bought a LX 50 with constant stalling problems. After much research, i got an unrestricted CDI from Scooterpartsco, and the stalling was a thing of the past. I then got thinking that the LX 50 was not very good on hills, which led me to looking at Big Bore Kits. I decided on the cast iron 80cc RMS kit which Scooterpartsco has on discounted sale for about $100. That's about 1/3 of the Malossi kit (aluminum though).

Thanksgiving 2024, I decided to install the Big Bore Kit - in my apartment! Bit messy, but I put down cardboard and plastic. Removing the engine from the frame takes about 30mins. The cylinder change takes about 2 hours for a novice - spent a lot of time reviewing the instructions I had made from Scooterwest's video. I did make two dumb mistakes - which I caught when I rewatched Scooterwest's video after I had buttoned up the engine. Thankfully i had not installed the engine in the frame yet - wasn't going to do that until I had triple-checked my work.

First mistake was that I installed the black plastic lower cam-chain tensioner guide backwards. So I had to remove the engine head to fix that, which in the process I noticed that I had neglected to install the new Naraku camshaft which Scooterpartsco had sold me - yes I had even pressed a bearing on it, but somehow put the stock camshaft back in the engine. So that mistake on the tensioner guide actually helped me to get the correct camshaft installed.

While I had the engine off the frame, I changed the sparkplug, the drive belt to a Malossi, the roller weights to 5.5 grams, a new Malossi red air filter, and a RMS rear shock absorber.

Messing around with the drive belt is a bit tricky, and I stupidly removed the kickstarter c-clip in the process of taking off the variator cover - which led to a lengthy fight to get the kickstarter spring seated again. In the end, you need a interchangeable bit screwdriver (with no bit in it) to put on the spring and push it while someone else puts the moongear into place. For putting on a new drive belt, compress the rear drum spring then use visegrips to hold the belt in place on the rear drum so you have slack for putting the belt on the front drum.

I did have quite a bit of trouble getting the muffler on and off, in the end I did it while the engine was out of the frame. I am not looking forward to having to remove it to change the rear tire.

Putting the engine back in the frame is easy if you have a motorcycle jack. I cranked over the starter, and after about 20 seconds, the engine fired up - the carb was fuel starved from being upside down during disassembly ( I should have sucked on the vacuum hose to fill the carb before trying to start the engine).

I drove it around for about 5 miles at moderate speeds, it ran well, climbed hills with ease, etc - but it stalled at idle. I ended up setting the air/fuel mixture screw to 2.5 turns out and adjusting the idle screw, which solved the stalling. I am running a #77 main jet at the moment - per Scooterpartsco recommendation - and a stock #35 idle jet. I have spoken with some Piaggio workshops in Italy and they told me to use #80 or even #84-86. I was told to keep increasing the main jet until it bogs, then to reduce by two sizes.

One unexpected thing is that ScooterWest video says that the LX50 takes 850ml of oil. I drained the old oil, then measured 850ml of Motul 10W-40 Break-in oil, but was only able to get 650ml into the engine before the dipstick was indicating oil level was at max. In the owner's manual it says that while the total capacity is 850ml, if you are doing a oil change you will only be able to add 650ml since about 200ml remains in the crankcase.

Summary of upgrades:
RMS 80cc 4T 2V cylinder, piston, rings, wrist-pin, and gaskets
Naraku performance camshaft + SKF 6201 C3 bearing 12x32x10 mm
Malossi 727x18.5x30 kevlar drive belt
Malossi 5.5 gram rollers
#77 main jet for carb
Malossi red air filter
NGK CR8EB sparkplug
Motul 10W-40 Break-in oil (will run for 600 miles)
RMS rear shock absorber
Carb bowl allen bolts

Scooterpartsco also sells a complete RMS 80cc Big Bore Kit including the main jet, Malossi air filter, and Naraku camshaft.

Some very useful items to have:
Motorcycle jack
Valve feeler gauge
Carburetor screwdriver set
Digital torque gauge adapter
1/4 drive swivel joint
1.5x strength reading glasses
Variator tool for front sprocket
Clutch tool for variator rear drum
Visegrips
Assembly lube
Blue Loctite
Black marker
1/2 drive breaker bar

An update:

I am now using a #80 main jet in the carb, and there is no bogging. I tried an #82 jet for a few months, it did not bog, but there was always the smell of unburnt fuel. Could probably go up to an #84 without bogging, but maybe more unburnt fuel. A #77 jet seemed to not move enough fuel. Which makes sense since the stock jet was #75.

I have re-adjusted the idle mixture screw by tuning the screw until the engine hits its highest idle point. It's about the same location as 2.5 turns out.

I ordered a set of idle jets, and am considering increasing the idle jet size from stock (#35) to a #38. The reason is that at very low idle when I increase the throttle rapidly, there is a 'pop' from the engine. I increased the idle speed, and that has removed the 'pop' when throttle is opened. But the new idle speed (with no pop) has the rear tire spinning a bit. I'd like the idle lower, but I don't want the 'pop' (and slight hesitation). So maybe a larger idle jet will help.

I also bought a Malossi Multivar kit in Italy for cheap and installed it. Note: do not install the plastic ring on the metal boss spacer, because that plastic ring is a speed limiter. I used the rollers from the kit (6.1g) rather than the 5.5g rollers I had in previously - I may change back to 5.5g.

To change the spring in the rear drum, you will need to use a clutch removal tool and a 34mm socket.
Mitch micbergsma has a good video on how to do this

Update #3

The clock on this LX 50 has been dead since I got the bike. I replaced the battery in the clock a few months ago, but the clock would only work intermittently, completely random and of course incorrect time. I messed around with the contacts in the battery holder, but no change. The old battery had corroded, so I thought the issue was residual corrosion on the contacts, but no. Turns out that the corrosion had gone into the circuit board.

Today I installed a new clock, you can get them from AliExpress for about $10.


Perfect fit and comes with a battery. The install process is similar to the battery process in terms of removing the handlebar covers and the dash assembly. The extra step is to remove the dash assembly completely from the handlebar cover and then remove the clear cover from the front of the dash assembly - with that off, you can remove the clock from the front.

Update #4 - lights

The stock lights on the LX50 are far too dull for driving in dangerous traffic. So I decided to put LEDs all around. So far, almost all good except for a small mishap.


I installed:

Rear LED signal lights BAU15S Amber with canbus
LED front headlight HS1 H4 Hi/lo Beam 6500k
LED rear brake light 1157 bay15d p21-5w White

I didn't install this, but I did try it (it didn't work for me because of variating voltage, but it may work for you) Rear brake light modulator or just use a strobe LED bulb 1157 bay15d p21-5w 3 flash red LED

For front turn signals, the pods are not very visible even with LEDs, so I removed the pods, and changed the front running lights into turn-signals. That's the way the LX50 was originally sold in Europe, much cleaner look. I cut the pod wires off, then soldered in a longer 2-strand 18ga wire from each pod harness down to the running light panels respectively. Then I cut the existing running light wires, insulated them with heat-shrink tubing and left them as hanging orphans. I soldered in my new 18ga wires to the now freshly cut ends of the running light socket. For bulbs, I used 1156 BA15S Amber LED Canbus bulbs. This is exactly the same configuration as the European LXs, except I have much brighter bulbs (LEDs).


In the process of messing around with the front turn signals, I saw many posts on MV about using a DRL/Turn-signal switchback kit that results in having white running lights and amber turn-signals combined (and no pods of course). Mitch micbergsma even made a video about how to install it. I bought the same generic kit that Mitch used and tried to install it on my LX, but for some reason both LED bulbs blew up after a few minutes of use. The resistors were very hot to the touch. This is the kit: LED Front DRL & Signal-lights BA15S with canbus. I don't know what exactly was the problem, but I can say that I did not get intuitive readouts from my multi-meter when I was looking at continuity and polarity on the wires. To be honest, a switchback kit has a number of potential points of failure (notably the chipset that controls the switchback). It's probably better to use something simpler.

While I was happy with my turn-signal only front panels, I decided to install dual filament bulbs with a low luminosity amber running light and a higher luminosity amber turn-signal in the same bulb. This requires changing the bulb socket from a BA15S to a 1157 BAY15S socket. This new socket is not an exact fit with the light assembly because it has 4 tabs in a 12-3-6-9 position, while the light assembly is 3 tabs in a 12-4-8 position. I cut off the largest one of the 4 tabs, then was able to wiggle it into the assembly without issue (used the gasket from the stock socket). For a bulb, I used a BAY15D P21W/5W Amber/Amber LED bulb. For the wiring, use the two wires from the turn-signal pair, and one hot wire from the running light. Use a multi-meter to figure out which of the turn-signal wires is ground (don't go by wire color). You do not need in-line resistors because LX50s do not create hyperflash. The LX50's turn signal relay is integrated into the dash IC board, it's not a removable relay. If you have another model does create hyperflash, then use inline 10W resistors.

There are also LED bulbs in BAY15D P21W/5W Amber/White. If you go with the Amber/White bulbs, make sure to get ones that have a low white luminosity and a high amber luminosity. Also note that these switchback amber/white bulbs have an electronic chip in them that doesn't work very well with variating voltage (I was unable to use them because they shorted out and fried the chip).


If you want to spend a lot more money, you can buy embedded LED light assemblies for both front and rear turn signals that look very modern. These have white running lights and amber turn signals with the switchback feature.

I am considering putting LEDs in the instrument/dash panel. They use T5 3W type bulbs.