Modern Vespa

Picked up this 177kit for my 78 P125X, along with the exhaust, and 26/26e carb:
https://www.scooterwest.com/malossi-166-cc-cylinder-kit-for-vespa-p125x-px150-stella-m3114935-m314093.html

and started digging in. Other than shooting a circlip into the stratosphere, and discovering a broken piston ring, there havent been too many surprises.

Now, 2 things I didn't plan on:

Determining squish
Determining if the ring gap is set from factory or not.

Scooterwest didn't mention either, but another suppliers website had a disclaimer about needing to know how to do this stuff, so now i'm trying to wrap my brain around both. Ive been watching the FreakMoped videos but even he's losing me.


Squish -
When it comes to squish, these are the numbers Im coming up with with my caliper:
-The base gasket is .5mm thick
-The top of the piston is somewhere between .5-1mm below the top of the cylinder. *the slight convex shape of the piston, and the slight chamfer of the cylinder edge makes it hard to get my caliper flush*
-The ring on head is between .5-1mm tall

I have no idea what to do with these numbers. The instructions say squish should be 1.2mm


Piston ring gap -
I pulled the cylinder off, and squeezed a ring inside it. Theres a very slight gap between the 2 ends, so i *assume* theyr'e gapped and good to go from the factory, but I have feeler gages coming in the AM to get a proper reading.


Any help would be appreciated. Im stuck until i figure this out...

It has crossed my mind that im possibly overthinking things, and I could probably button this thing up and be fine.

No, I don't think you're over thinking it.

Piston ring gap should be fine out of the box… no need to grind the gap down.

Set the squish to 1.2mm sounds good. Measure the port timing would be good just to know, unless you have a number in mind.

Match the ignition timing and some basic jetting and it all should be pretty good.

I usually check piston ring gap, even on new parts and measure piston to bore clearance because I'm OCD. Ring gap is quick and easy to check. Most people check piston fit by feel. It's more important with used parts or if quality is in doubt.

I have this kit and love it. My main takeaway has been Malossi knows what they are doing. The rings are gapped properly out of the box. If you use a stock crankshaft and the furnished base gasket the squish will be perfect too.

I would not have gone with a 26.26 carb for this kit but, since you already have it, give it a go and see what you get.

Squish I go the lazy route and stick a piece of electrical solder onto the crown of the piston, bolt everything down and spin the motor to squish the solder. Remove and check the ends of the solder. Don't be afraid if both numbers don't match. Guess and check till you get some experience.

Ring gap I'll check. Push them in with the piston so you know it's level. .25-.4mm gap is what I'll shoot for. Most of the time you'll be good.

Remember, Malossi rings are trapezoidal. Don't put them in upside down. Malossi instruction book should show the orientation.

Rings for the cast iron kit are not trapezoidal. You should still install them with the printed side up, though.

No offense and no disrespect to the people that do piston ring gapping and squish cylinder head stuff but why? I have the same cylinder kit which I put myself last year and I did nothing to it and it runs fantastic!! In fact, I never done piston ring gapping or squish on the cylinder and I never had any issues.

All I am saying is why not just to slap on the cylinder and just start riding it? I can assure you that it will run just fine.

I love my Malossi 177 Cast Iron. I am running it on a LML newer engine (a year years old but very low miles). I slap it on and I put SIP SR3 and it rips. It is significantly better than the Malossi 166cc on acceleration. What a great value for the money this kit truly is.

So i buttoned everything up early this morning. I drove the studs in tight until there was about 40mm sticking out after I put the cylinder on. That left me with enough room to have 4-5 threads sticking out of the nuts after torquing to spec. Im happy with that. Im not sure if the rings are installed writing-side up, but I do know theyre not trapezoidal, so im letting them ride as-is.

Someone mentioned the 24.24 carb being a better choice(i thought so as well), but the 26.26 is what scooterwest recommended, so I went with it.

I dont have a fast flow tap at the moment because Ive heard conflicting stories about whether or not theyre needed. I did drill the float bowl in the carb. If I run into starvation issues, ill get the tap.

Going to get the static timing set today @ 18BTDC, and try to figure out a good starting point for jetting. I know I saw a post around here somewhere about jetting..

I run fast flow taps on mine. Two of them failed after a few years. One of them would give me intermittent flow and the other one was leaking and old but the OEM(original manufacturer equipment fuel valves) works just fine too.

Like I said, I converted all 3 of mine, two because of necessity. The only down side that I found is that the reserve is now huge. Also the switching level in which you suppose to switch from "On" to reserve is very sensitive. The engine sometimes doesn't start because if you have it in on it thinks that you are in reserve and when you are in reserve it think you are in on. This happens specially when you are about to start the scooter and you kick the kick pedal and the fuel moves inside the tank left to right causing the fuel pick line (metal hose) to not know what source to pick from.

Lastly, one of the fast flow that I picked is wrong. Now what On use to be is reserve and what reserve use to be is on. Other than that they are not expensive and is good maintenance to have because it is a few years down the road before you have to replace them again.

So the final build will have:

177kit
special road 2.0 exhaust
26.26 carb with drilled bowl/drilled filter

Im looking at the jet stack that malossi sent me, and Im a bit confused.

190ac/BE4/115

Iv never read of a 177 kit taking such a small main, or high ac. Does anyone have any other recommendations before I head over to scooterwest?

Way too lean! I'm running a 160,BE4, 130 on my PX with a similar setup but the 24/24. Since you've got the 26, I'd say a few points higher on the main.

You're going to be in somewhat uncharted waters jetting a 26.26 for this kit.

The AC190 sounds weird. The kit is supposed to come with a 52/140 idle jet, a BE4 mixer tube, and both 105 and 115 main jets. The 105 is for stock rotary intake. The 115 is for rotary intake if you have a cut crankshaft. It assumes you will reuse the stock AC140.

I would start with an AC140/BE4/MJ115 and the 52/140 idle jet. Without a cut crank, I would expect to walk the MJ down a bit from there.

Yeah, I'd expect a 160 or, more likely, a 140 AC. 130 MJ sounds right with the 160.

I don't know about the 26/26, but >125 MJ is float passage drilling territory on 20/20 or 24/24.

What's funny is that I found a 190 AC in my jetting stuff a while back and wondered where it came from. I'm guessing it came with my Malossi 166, which also included a BE4 and maybe a main, but I don't recall exactly.

OK, so far we've got:


AC160,BE4,MJ130

AC140/BE4/MJ115


with the recommended 52/140 idle.


Heading over to scooterwest for mains, a flywheel puller, and piston stop.

You buying a new one for us if it doesn't run just fine?

Probably came with the carb. Every new carb I buy from SIP comes with a 190 AC. Goes straight in the garbage and swap.

Don't forget the flywheel holder!

Buy a set of main jets. It's not much more than buying a few individual jets and you'll be guaranteed to have what you ultimately need that way.

Let us know how it goes.

Oh, you guys will be the first to know.



I had to pull the cylinder/head back off to replace the wristpin circlips. I stupidly thought I could reuse the old ones, and mentioned it at the store. Luckily the guy was paying attention and told me I cant. So I went back in, replaced the clips, and ensured the piston rings were "writing-side up". Buttoned everything back up. While i was at the store, I asked the guy to recommend a jet stack. He wrote it down, and I promptly lost the paper between there and here. So any advice on a starting point would be appreciated.

To start with on a 26/26. Jet it so you can ride it but know it's rich.
AC120/BE4/125 and 52/120
Once you decide it's run in, then begin leaning down.

The inside top cylinder stud enters the casing on the edge of the autolube drive gear.
If you are using autolube, I would take the clutch cover off and check there is still clearance between the stud and the drive gear. It is possible for these to touch and strip the autolube shaft.

THANK YOU. Is there a measurement i can use to ensure i clear the gear w/o having to inspect the clutch? I dont have a jack to get the back end off the ground. If possible. Id rather just pull the head and adjust the length of the studs.

Update: Got it all together, brought it outside and it started right up! Sounds great and feels like an entirely different scooter! I love it.

Currently using 120ac/be4/125main,
But everything after 1/4 throttle is spluttery.

Too bad the weather sucks right now.[/i]