Modern Vespa

So I drew up a 3mm version (160 duration) and a 5mm (170).

I'm probably going 3mm. I can always carve more later. At 3mm, I can even go backwards a bit if needed, I do have that 1.5mm spacer under it, so I could swap for head gasket if needed.

Much better plan than doing the whole schwack at once.

If you will do the sound capture and share them with me, I'll even generate the GSF Dyno charts for you so we can see how the changes affect performance.

Piston is cleaned up. 20/20 carb is clean.

Be really careful going wider on the exhaust port. Those fat cast rings fail somewhere around 65%, for total safety keep it under 60%.

These are drawn at 60% and I can stop short on them anyway.

This is exciting 😁

This is why I buy greasy's cast offs, I have an extra 2 port top end if I need it. Let the experiments begin!

Drilled heart air filter or not drilled?

Not drilled. You're not going to be pumping enough mixture with a 2-port 150, even if you extend max RPM's with the pimped out exhaust port.

Don't drill out an original Piaggio filter!
Ok maybe a 5mm hole above the MJ, but you will not get any more power drilling it.

I have one of each so I can start undrilled and if I get curious I can swap it out. Thanks!

Drilling the filter theoretically allows more airflow through the air corrector.

As I've gotten more comfortable around these motors, I've come to believe there's no way it could make a difference, because there's more than enough space around the top of the AC & Idle jet to provide bleed air to a 1.6mm intake.

The difference is pressure. Undrilled filter takes air in from the side at the top of the Venturi. Drilled filter draws air from within the filter. Slight difference in pressure but a difference none the less. With a T5 filter the difference is more significant.

I get the idea: When the AC/Idle's intake area is exposed to the filter, it's going to *reduce* the pressure over the AC/Idle, as the carb generates negative pressure inside the filter, which would in turn richen the mix ever-so-slightly.

That may have made sense back in the pre-Internet days when getting jets was not as easy as it is now. Today, though, it seems like a really poor way to tweak the AC when it's possible to just go buy a richer one if you need it.

so let's wager some ham

how many RPM is the package worth?
-sip road 2 in place of stock exhaust
-20/20 carb in place of 20/17
-160 exhaust duration in place of 150

I'd be really pleased if 500 RPM showed up (raising max to 6500), making it a comfortable low 50's bike and topping out at 55 or so. Is it realistic?

I'll go +750 RPM's in third gear, but dunno if you'll be able to get there in 4th.

fair point, I was wondering that myself. the old primary gearing question....

do they make a 22 tooth clutch gear that mates with a 65 tooth primary?

(edit:) yes they do, DRT does: https://www.sip-scootershop.com/en/product/clutch-gear-cog-22-26-teeth-drt-for-px200-clutch-for-primary-65-teeth-for-vespa-200-rally-p200e-px200-e-lusso-94-cosa-1-200_13082800?usrc=gear%20clutch%20cog

I'm running a 7 spring in there, so this should be the right one.

I thought the same thing, but the DRT gear was slightly bigger and wouldn't fit. I am running a 3 speed though.

It took me a while to figure why the clutch wouldn't seat. I thought it was the woodruff key. Nope, the actual gear itself...

I'll see if I can find the post I did about it, with measurements.

Are you talking about this?
The tale of two rebuilds - VNB2 and VNB5 (Post 2482720)

If so, it's the old reverse situation - you're trying to go 23 from a 22, probably with the 67 or 68 tooth primary. I've got a mated 23/65 from a P200 setup in mine, and would be going to a 22 made to mate to a 65.

On my blue Allstate with the 2 port Pinasco I tried a blue 20.20 filter, no filter and a drilled 24.24 filter. The drilled filter runs the best.

I also had it out today and had some WOT in 3rd and hit 6200 rpm's. No fancy stuff happening. Just installed the jug and swapped a SIP road 2 and a 20.20 carb. Haven't checked the speed with a GPS yet though. My 60mph speedo needle is buried though. So I'm pretty sure it tops 60mph. I'll run my gps tomorrow to see.

Ahh, correct, disregard

The precious has arrived, my precious….

can anyone snap a pic of where the second spring should go on the cylinder? I can drill a hole for it while the cylinder is off.

so the google returned my own post from my p200, where Safis showed me.

SIP Road 2 springs (Post 2197382)

the other thing that's been on my mind is the question of all of the flavors of 2 port engines. i'm not really sure what this top end is, there are versions going from 5.5hp (VBB) to 7.1 hp (sprint with higher compression). i wonder if my head is the low compression or the high compression variety? it would make quite a bit of difference if i had the low and went to the high.

any way to tell?

Measure the head volume and use it to calculate compression ratio. The ratios are all published, so you know what number you're looking for.

And are you concerned that you have high and need low, or vice versa?

Unlikely a bajaj head will be higher compression.
Any more heads in stock to choose from?

I'm concerned I have low and am missing out!

I will have to check the stash, but I think all that's up in there are 125 heads. I might have another 2 port head though, now that I am remembering I bought a 3 speed 2 port engine from greasy for fun and he threw a bunch of stuff in there.

So close…

Max rpm was 6810. Max temp 265°.
Pinasco 2 port plug and play.
Sip road 2 exhaust, 24.24 drilled filter.
Vape ignition 18°
160/BE1/112
40/130 idle 3.75 turns out. Still a little choppy at the start of the throttle. Have 2 richer jets on the way.

Useful data - it seems 7000 RPM is a tough target without getting into opening up the intake duration more then.

Did you try it on a 110 main? 265 is pretty cool for a max temp.

Let's keep it to my topic here, this could get detailed. But I'm totally interested to follow it in another thread!

I'll post up in my thread as well and we can discuss!

Just wanted to share that data for you

So inventory has another Bajaj head that might be different volume. It's kinda hard to tell, but the bowl profile looks smaller.

I could steal one from my Stella engine, but that kind of sucks. I might borrow it to cc it. I'm gonna try and measure the volume on these 2.

The cleaner head is the one from inventory.

The heads are roughly the same, about 30cc by eyeball. That big of a change in CR should be at least 5cc, maybe 10 by math, which would be obvious. It gets complicated because it should be volume at transfer port close vs the volume of the cylinder head - dome of piston, blah blah blah.

They look very close.

Gonna have to have a look at that Stella head.

30cc, even with full dome piston, is not going to be high on a 150.

If one of those heads met with a belt sander until near flush, it could be enough.

Yeah i need to measure properly before I bust out the sander so I can see what I actually remove.

But first, I want a look at a later head, so I'm gonna have to pull it from my spare Stella engine and have a look-see.

One realization I had on the way into work - I can't belt sand the head. I already had zero squish clearance without the base spacer. I used a 1.5mm base spacer just to get to acceptable squish. So maybe there's 0.5mm to play with, but if CR is to go up, it has to come from chamber shape.