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.

Is that measured without a base gasket? If so, you could take the gasket out and measure again. Just use sealant if you want to reduce it down to the 0.8 that Malossi recommends.

Good call, I just had to do that on a cylinder recently. There were two different gaskets supplied with the kit, but both were to much to get the squish to the recommended spec.

Hello Declan, apart from building quality, is any diference in performance?
First I want to take it easy, SI carb and fixed timing. Better carburetor and expansion exhaust, later, may be.
Thank you!

Hello Ginch.

The base gaskets are 0.5mm + 0.18 to get the 0.92 -0.94mm squish. That is the nearest I am from the 0.8mm that Malossi says. I have not found any thinner gasket.

Thank you!

You can run no gasket, just sealer. I have had good luck with Blue Hylomar, but someone suggested recently that Reinzosil may be even better.

Looks like you need 0.12 - 0.14mm thick gasket, they seem to start at around 0.5 as you've found. Next option is to cut one yourself from some other type of paper, I saw one guy mention he used a manila envelope which he found to be a relatively strong paper for it's thickness, which was 0.13mm.

Personally, I'd be happy with 0.94 but that's just me.

Vukan, could you point me in the direction of a howto or simular to replicate your squish measurement ?

I assume you measured the depth of the head and subtract the protusion of the piston?

I'm starting to build a P200 with a Malossi MHR 210 (2016).

Jacob

Better a couple of photos. A piece of solder tin, fixed with tape. Asemmbly the head at its torque. Turn the engine so the piston gets the top and passes it. Measure the solder tin. Try diferent thicknes base gaskets until you get the squish objetive.

Nice clear demo. I like to have the solder touching the cylinder wall and measure at this point, together with measuring the inner squish edge. With both measurements, the distance at the outer edge subtracted from the distance at the inner edge, with a few sums and a little trigonometry, these will give the squish angle and squish area. This info determines how aggressive the head is, which in turn could be used to assess the ignition timing requirements, manufacturers suggestions or if the head needs modifying for your application.

It felt like the Polini reved up more freely and had quicker acceleration, but the two motors weren't 100% identical. The better exhaust clamp is worthwhile in my opinion.
The Polini may have also had a bit more clearance, but I don't have both bikes anymore.

Vukan, the squish gap you have there is good, don't bother complicating things over that last 0.10mm. Your measurements and method is spot on, leave it alone and button it up.

Thank you, i will go on assembling, it is the first time, and you know,

Thanks again for sharing your experience mates.

Regards.

Dear Mates!

It started at third kick! Very happy with it.

I have more doubts about the jetting now, I tried to go rich at first and the idle jet is a 65/160. 140, BE2, 145 main. haven´t reachet to 1/3 throtle yet, but it doesn´t look very rich, neither lean. Only 4 cicles of 5 minutes static break in.

Malossi 210 sport (2016). Ported.
polini advanced crankshaft, 57mm stroke.
Pinasco 26 vrx ventury

If you have any advice, they are wellcome.

Thanks again.

Best regards.

Did you pressure test the motor?

You probably need some more time on the motor to see much color on the plug.

One thing that had me stumped with a similar setup is that I had a mix of Dellorto and SIP main jets. I didn't realize that SIP had changed their numbering system from that of Dellorto. I was running a Dellorto 142 main jet, seemed slightly lean, jumped to a 145 main and had a soft seize. I have been measuring jets with one of these tools now when I make changes.

No, I did not.

Yes, it is first start, now tuning needed.
Some jets are BGM, but yes, I will look for a tool and verify the size of them.
thanks for the advice!.
Regards.

Link to that tool?

Dear mates,

What do you think about this plug chop?

Malossi 210 ported.
advanced Polini 57mm crank
vrx 26 pinasco, with sip T5 filter. (It was imposible to jet with it´s ventury).
Big box touring exhaust.
NGK BR8ES plug.
Sip vape at 18º. Static.
55/160 idle
In the Photos it was a 180/be3/152.
Sensations, spluters a bit if open throttle. Today i put a 190 air corrector, feels better not plug chop yet.
Opinions?
Thank you in advance.

Regards.

Hot. What other air correctors have you tried?
The 26/26 Venturi does jet in, I had a vrx vortex on my 200 for the last 15000 miles.

Thanks for the reply.

The pinasco ventury is off now. The only ventury is the proper that has the T5 SIP air filter, with 5mm and 8mm holes on it.

I have tried 140 with be2, as I read thar it was richer. But it was worse. (With pinasco ventury)

The engine has about 300 km.

Tried with 160 be3 and 145, 148, but is like lean at wot, and does not reach to the top. and bogs when open de throtlle. (With T5 filter).

As I said now trying the 190. Lets see, today i have done 18km to work.

Al suggestions accepted. I read people with SI carb and 221, 225, 210 engines, so it must be possible.

I am new jetting a engine from 0. It is my first complete build. Learning in progress.

Thanks mates, regards.

Does the passage from the fuel bowl to the main stack is larger on a Pinasco compared to stock si 24 ?

Yes, in the vrx.

The special models of Pinasco carburettors "R" were developed for the world of racing and for the most demanding tuners. The changes made to the Pinasco carburetors "R" increase the performance and allow an efficient and accurate carburetion. All Pinasco carburettors marked with the letter "R" have the internal passages CNC machined to guarantee the right flow of fuel and to eliminate the effect of "empty gasoline", also the passages of the float chamber cover are completely machined to allow a perfect filling of the float chamber. On the models SI 26/26 "R", the "Venturi" has been further CNC machined to increase the standard diameter and get the maximum size of 26.00mm compared to 25.40mm of the cheap model. The carburetor "R", with regard to the SI models, is the TOP of the range and it is a Pinasco's sole model.The carburetor R is also available with the classic venturi VRX billet, also the range has been extended with the new venturi VRX dedicated to all the carbs 20/20

How many km's on that plug?

I have a very similar setup.
Started: Drilled filter, 160/BE3/135. 55/160. It was rich.
Few weeks later end-up:
No filter, 145/BE3/130-something, as I reamed it to idk from a measured 130. Guessing 132 or so. Rides great. 1/4 throttle and WOT plug checks look great too.

Big AC with that filter can lead to $$ trouble.
It's also difficult to dial-out barely open four stroking, as that filter was made for a different (shorter) carb.

As Ray said the T5 filter is for a different carb, also 24mm not 26mm. Put the 26mm vrx vortex back on and jet that in.
When not track racing and needing to actually ride smoothly at low throttle, AC120/BE3 is where I begin.

Thanks to both,

Smallest AC I have is 140, I am going to buy the 120, 145?, put vortex on and try.

Ray, the plug is only less than 300km, as the rebuild.

Regards.

You can get the 140ac to work. 145 doesn't exist. I reamed my 140 to more or less there.

What other jets do you have?
And is that plug pic a "plug chop?" ie did you ride at a fixed throttle position and kill the motor?

With the vortex installed I'd get this set to try:
https://www.scooter-center.com/scooter/p-18047.html
Read the description.

The vortex adds a complication to jetting. If you have a stock filter no holes it will be much easier. Unfortunately the only new available filter is the Cosa/drilled, which is also a complication but less so.

And sorry, I forgot to mention my carb is a Spaco 24 with the channel to the MJ drilled 2.7mm. Float assembly not yet modified.

I have this complete kit, from 58 to (68/160). I started with the 62, and down to 55/160 for now.

Also the 50/140, no tried.

Main jets from 125 to 162 I think.

Mixers BE2 and BE3.

I have read the link, so the smaller Air corrector, enriches the uper range of rpm. There should be my mistake. I thought more air, more fuel, more mixture at every range.

The plug chop was made on 3rd gear at wot.

Thank you for the advices!

Regards.

I think what they mean is a smaller ac in the pilot jet will be relatively richer in the throttle ranges vs a larger one, aka its influence in the range is longer.
The same for the AC in the main stack, but in reverse.

Are you going to try to jet it with the bellmouth/venturi?
If so, try 10-15 pts more than a filter. As my 135 was rich I'd try a 150mj*/BE3/140ac.
*Elephant in the room, you can't rely on stamped numbers unless maybe you have a KMT set. Get a sewing needle kit, mark the tip with a Sharpie and at least put the jets in order based on where they score on the needle. Unfortunately, the larger size jets are farther off their stamped #'s.
Same with air correctors

Safe MJ will provide the most power up a hill. This can be done on a flat road and reduced, but a decent hill will take gearing and your weight into account.
Lean or rich will be less power, but of course start too rich and go down.
Ignore the pilot circuit response (from closed to mid or so throttle), as this will have to be jetted once you've found your safe MJ. Avoids going in circles.

So after some months how is it driving ? Are you satisfied with the setup?

Jacob

Dear colleagues,

Thanks Jacob for your interest.

I'm very happy with the engine, although I haven't been able to ride it much these last few months. 1500km since then.

If I had to find a fault, it would be that even at high RPMs, the spark plug is still lean color and runs a bit hot. I don't keep it at high RPMs for very long.

I want to do the next test with AC120. Right now I'm running AC140 with BE2 and 135 main. Pinasco SI 26, ventury and airbox.

But overall, I'm happy with it for the first engine I've rebuilt,

Thanks guys for your advice.