Modern Vespa

I did my initial jetting with the scooter on the center stand. I started out with a 138, then a 132, then finally a 128. I have my throttle tube marked at 1/4, 1/2, 3/4 turn, and the engine got more spluttery the higher i revved the engine. So i just kept going to a leaner MJ until the engine stayed at the same sputter throughout the whole rev range. Then i went for a easy test ride. I was going to do a couple heat cycles before i do some plug chops.

I just checked at SIP and i don't see a 55/120 as an option?

128 is a good size main jet. Often works out ok. Riding around under 1/2 throttle Will help.
Keep an eye on the rpm when revving on the stand. At this stage it should get more spluttery as the rpm goes up.

I make my own jets and forget which ones you can't buy. 55/100 like the LBD of pilot jets.

Good to know!

55/100 or 55/120? It looks like your recommendation changed between your last couple postings...


When you say that a 128 is a good size and that riding under 1/2 throttle will help, does that mean that you think a 128MJ could be a bit too lean?

On behalf of the deer within a 1/4 mile of you, I'd like to protest jetting on the stand. Surprised they didn't give you the middle hoof as you rode by.

140/BE3/128
Take it to a decent hill. WOT uphill and pull the choke.
If that gets you any more power you're lean.
This can be done at any throttle position but sort the mj first.

1/4 mile? Those tick taxis were just on the the opposite side of the road ready to give me the boot. If i can see two deer, it means there are four more hiding in the bushes ready to jump me.

I got plenty of steep hills here, so i give the choke pull a shot.

Lemme take a stab:
" 128 is a good size main jet. " with ur set up - this should be ballpark
" 1/2 throttle Will help." this is eithe directions to avoid deer, or a statement about knowing if your on the right main by riding at half throttle. Not sure.
" Keep an eye on the rpm when revving on the stand. " could have meant: don't blow ur motor up - but was followed by modifier " At this stage it should get more spluttery as the rpm goes up." meaning it should no longer just take off on u when u have it on the stand.
🙂

That said - everyone has their own methods of getting a read on jetting status. Once u get a read - changing jets is the easy part.

Since u r getting some good - but different - suggestions on the read part, here is my $.02.

Ur riding conditions affect ur tuning decisions.
U seam surrounded by rolling hills - and well, deer.

I like Rays uphill tuning.
It puts it under more then flat road load.
Kinda the exact inverse of stand.

At this point, it can be as simple as taking some extra jets with u and running the same hill a few times.

3rd gear and 5/8-3/4 throttle preferred minimums.
If u go down a jet size and it gets more powerful on that uphill - then ur improving.

If u can't feel any change, make that same run, at top of hill, hit kill button, coast to stop next to the deer. Pull the plug. Black? Rich. Gray? Lean. Milk Chocolate hues - oooo. Yummy.

Doing this on hills will avoid jetting too lean.

Mix and match any of the above for success and find ur fave manner.
Then apply now and future.

Currently while the scooter is in the center stand, it will rev about 300rpm higher at 3/4 throttle than at full throttle. Oh, and the max rpm is now below 10k...maybe around 9700ish.

I'm pretty sure that's what Jack was saying you should be experiencing.

Full throttle is too rich - this won't rev out.

So if it were me, I'd apply the hill climb with jet walk down and plug check methods described above. Longer run better than short if u have it.
At be they have better/ preferred method.

Think u r past the choke pull - as ur showing signs of rich on stand.
But u can also do the choke pull to see if it confirms.

Either way - sounds like some leaning out is in order - and it will improve both performance and mileage

For throttle indicator I went with a 3 point indicator, closed - 1/2 - WOT. I went with this because si carb and wasn't tuning a needle carb. Most of the time I cruise up to 55 and below half mark. It goes past half on acceleration momentarily but rolls back below half when cruising not thrashing. Past half needed to go above 55 which is not much and I've not done WOT in 4th too scared.

One time I was way past 1/2 mark and not going 55 then realized grip rotated. When it gets hot here sometime grip slides it's a little out of calibration in photos. Think having a 1/4 mark is too imprecise and noisy for my needs.

The pilot jet at this point is unlikely to be perfect. The final correct jet will definitely be somewhere between 55/140 and 60/100. All depends on the main stack. 55/100 is easy to buy and safe.

I think the 128MJ could be ok. 1/2 throttle cruising, combined with going up hill is where this can be decided. Do the wot tests as soon as you can. This will get the AC done and everything else will follow.

Jetting on the stand, gets it all fairly close and finalise one the road. Should always feel slightly rich, yet revvy on the stand. It's never going to be fully hot and it's revving without the throttle delta.

Derp...
I just removed the existing jet stack that was installed and it turns out it wasn't 120/be3/128 like i said it was...it was a 140/BE3/130. I seriously don't know how that happened, but there's been a lot of stuff going on in my head this week, so maybe i'll just chalk it up to a major brain fart?

Hopefully no damage. Lower end is probably not bad but always the sustained higher rpm that's the issue.

I'm a brain fart master.
Learned a lot from brain farts, though.
Quick example:
Rode off downhill with no main stack at all. It rode, sorta, on flat roads.
I was able to feel the influence of the pilot circuit.

That stack "should" be very rich on your bike.
Any hill tests yet?
Free/superior dyno.

I haven't made the time to mess with it just yet. It's either been rainy, or i've been out cutting and splitting firewood when it's been dry. Before i go further with my jetting, i'm tempted to swap out my Sito+ and go back to the stainless JL Right pipe...

I like the idea of putting the pipe in u like.
And smoking it.
Or jetting it.

If ur gonna out the time in to get it where u want it - might as well have the pipe u prefer.

One vote fer

It's been a few months, but i'm back here looking for some more carb advice (AGAIN).

I just bought a brand new 24/24E carb from SIP. I also have two different floss bowl covers to choose from. One is for a 4.5mm float needle, and the other is for a 5.2mm (this is the 5.2mm https://www.sip-scootershop.com/en/product/float-chamber-cover-dell-orto-si-2020h-vespa-cosa-125-150_12829540 ).
Is there a benefit to use the 5.2 cover on this particular 208 engine? Interesting enough, the inlet holes that the rubber needle tip blocks the flow are the same diameter on both sizes of covers.

I did come across this interesting thread... Carb modifications

I vaguely recall that freakmoped tested both in for flow and the bigger needle was slower. Or no better, can't recall the details now. But you could check his videos.

I remember watching that video a few years ago. I'm wondering just exactly which two bowl covers that he used. All the other research that i've come across is saying the opposite of Freak Moped.

Drill out the 5.2mm body to 3.0mm. Check the banjo hole is swarf free. Then you have the best SI float top possible.

I'll have to search out a 3mm drill bit. I figure i can burnish the brass portion of the hole with a bamboo chopstick. Interestingly the body on both float tops are right about 2.2mm.

I never did dial in the jetting from however long ago, so i thew a tarp over the scooter as a temporary fix. I did decide to removed the JL Right pipe and swap back in a Sito+. I'm also switching out my variable Vape ignition for a static Vape. I'm hoping to give it another go here…

The engine is still a stock cast iron jug with a SIP zero squish head and a 60mm crank.

24/24 carb
150psi compression tested


Anyone have some input on what i should set my base timing at on the stator plate? I think 23 degrees would be way too hot for a warmed over engine like this.

I'd start at 18 degrees with that much compression.

Let's say a guy wanted to have a more reliable engine with a 60mm stroke…could he simply remove the SIP head and swap back on the stock head (along with having the huge 3mm+ squish)? If the compression is lowered back down, would the timing then be set at 23 degrees?

Still no, if I can guess.
Strong, no-float Vape spark.

What about if i remove the SIP 60mm crank and swap back in a 57mm (along with a stock cylinder head)? That would put me all back to stock P200 spec. Then surely i could set my static Vape timing back to 23 degrees? Or am i missing something?

Vape instructions call for 18° if I remember correctly

For their static version on a stock 200 engine?

Yes, you'll be fine setting your static Vape ignition timing to 23° on a stock P200 engine.

Vape doesn't recommend any timing in their instructions. How could it? The correct timing for an engine depends all sorts of things peculiar to that engine. It's not a one size fits all thing.

How much squish clearance does this have? If 1.2mm, set the vape timing at 18 degrees. Jet it in and enjoy it. I would say it will be no more or less reliable than bone stock.

Obligatory reminder, even the "static" version isn't really static. It has a little bit of early advance, followed by auto-retard, whereas the Ducati is as flat as they could make it.

Personally, I don't see why you wouldn't take advantage of the 60mm crank to get squish down to 1.5 or 2mm and run with that. That'll give you a better performing motor that will be dead reliable, just need the carb a little richer than stock.

Whoops sorry, VMC instructions say 18°.

Sip says 18-25° depending on what the cylinder asks for.

If you tighten up squish you will need to retard the timing.

With a 60mm crank, an MMW head, and a stock cylinder, I'd use a 1mm base gasket. That should put your squish around 1.3mm. Then dial your timing down to 18-20°.

My notes show that i have it at 1.5mm

Then I'd just set my 4k rpm timing to 18 btdc and run it. I'll bet you never see 300f on the cht.

QA Scott did this or a very similar o-tune-ish build on one of his p200's a couple years ago and he loves it.

Yeah, I opened up the exhaust and piston a bit, but still have the 57mm crank. And I sanded down the original head to get the squish down. I forget what it is now. And I'm running the original CDI.

I did put Vape static AC on the VNB and the VBB and set the timing about 20 BTDC. All is good so far 🙂

With 1.5mm, will get away with 19@4000.
Will need richer jetting than usual.

Disregard this.
I was thinking points to Vape like my P125's and 100 Sport. Not the P200's
When Piaggio went points to EI, advance went from A to IT(18).

Is your crank the SIP-branded Primatist?
Awesome crank

Btw, timing can be adjusted on the Vape accurately and easily, using the 1mm = 1 degree marks on the baseplate.

Yes, it's the fancy pants 60mm SIP crank. I bought it back when they were fairly affordable. My notes show that it's the one with the 125/-5 inlet timing.

Isn't 18 btdc about the same timing you'd set a malossi 210 kit at?