Modern Vespa

Hello colleagues,

I am assembling my first vespa engine, I will tell you a little about how I intend to do it. The engine is a 73M px iris 200, 1987.
Malossi sport 210 cylinder with its Malossi cylinder head, It is the 2016 model, not the last one.
Engine casing with enlarged ports and enlarged rotary intake according to Malossi manual.
Polini crankshaft advanced with stroke 57.
Pinasco vrx 24 carburetor with its venturi. The diameter of the carburetor is 26. I currently have this carburetor on the stock engine, I ordered a 24 and it came in 26mm. I think those are the important things about the configuration.

The goal is a reliable touring engine... and the faster the better.

Now comes the main question and it is about the ideal squish.
On the one hand, Malossi recommends 0.8mm. On the other hand, I have read that closer to 1 mm is better. Malossi says 12.5-1 compression.

I have also read that when breaking in the engine, a higher squish, or lower compression, is advisable, and once the engine has been broken in, correct it and lower it to the recommended 0.8mm.

A larger squis than recommended, I have also read that it is not good since it takes more temperature...

I don't know how important it is, we're talking about a difference of 0.2mm.

I have the different joints for it, and I would like to close it and not touch it anymore if it is possible. Right now the squish is at 0.92-0.94mm. Not closed the head.

How do you see it? What do you recommend me?

Ah! I have two cdi options, fixed and variable vape. The fixed one at 18º, but what about the variable one? 23? 22?
Is the variable worth it?

Thank you very much in advance. Kind regards.

1) Run a 24/24, not a 26/26. It'll give you better gas mileage for touring and be easier to set up. Power difference will be negligible.

2) What are your port timings?

3) What exhaust are you running?

4) Squish should be in the 1.2-1.4mm range. Don't worry about setting squish until you have your port timings set.

4a) I've never heard the "break in with lower compression/higher squish" before. My personal break-in method is "three heat cycles, then ride it like I stole it," and I generally build much more aggressive motors than you are.

Your instinct to avoid opening the motor unnecessarily is correct, IMO.

5) Start with the fixed timing CDI. Variable is faster, but takes some experience to set up right. If you get it wrong, you'll hole the piston and kill both the piston and the crank.

6) Make sure your motor passes a pressure test once you have the cases & top end sealed, but before you install anything else (e.g. clutch & flywheel) in case it fails and you have to track down an air leak.

And welcome to MV/NSM! Share some pictures of your bike and motor. We love pictures here, and are also REALLY good at looking at them to identify & solve problems. Even problems you didn't know you had.

Vukan, rule of thumb for squish is 1% of stroke on race engine. That means 0.57mm is minimum, but in reality not safe on Malossi piston because of weight which is more than on comparable race piston. So Malossi recommendation of 0.8mm is feasible as it is a safe margin. Anything above this amount and the squish effect is diminished, meaning the fresh charge turbulence is reduced below ideal speed. In other words, if you go above the minimum amount of 1% it makes no difference if your squish is 1 or 2.5mm.

You will get other recommendations, but I'd go by what Malossi wants. They did the research for their cylinder head. The only reason you'd increase squish is if you were using an older head with a wide squish band and need to tame the turbulence.

Hello colleagues,

I have been out some days. First of all, thank you for your replys, chandlerman and pullmyfinguer.

Answering the questions:

1) Run a 24/24, not a 26/26. It'll give you better gas mileage for touring and be easier to set up. Power difference will be negligible. Ok, noted

2) What are your port timings?

Is the firt time measuring them:
Exhaust port: opens 93º after TDC., Closes 269º after TDC. 176º exhaust port timing.
Transfer ports: Opens 123º after TDC, closes 239º after TDC. 116º transfer por timing.

30º blow down.

Rotary valve: close 79º after TDC, opens 246º after TDC.

At this point I am really lost. Cilinder timings are standard from Malossi 210 sport. the rotary valve is open as Malossi says. The cranckshaft is a advanced polini 57mm stroke. Could anyone help about these values? Are them ok?

3) What exhaust are you running? Big box touring.

As told in my first post. The squish is right now in about 0.92mm.

Fixed CDI at 18º as Malossi recomends.

Presure test on the way.

On the other hand, "pullmyfinger". Thats what I think, Malossi have had done some test to declare the 0.8mm squish. I am quite dubitative for these reason and so many diferent opinions.

Thank you very much for your help.

Best regards.

I have used a BGM big box and a Polini box with Malossi setups. I personally prefer the Polini, but both are great. Quality was better, noticeable better clamp. Had my past few box pipes ceramic coated, this really keeps them nice looking.

If your running a box pipe use fixed timing.

I noticed a pretty big difference between the 24.24 and and a larger HRA carb. I liked the slightly bigger carb for blasting around town, but if I was doing longer trips maybe mpg would be an issue.