Modern Vespa

Been a while since I have posted here. I have been riding my BGM kitted Stella as is, and I was able to take it to this year's Smoky Mountain Smallbore Rally. This year I got to put it on the dyno and I made 13.6whp!

For reference here was my full setup:
2009 Stella, no case porting
BGM 177 kit, no port matching, 0.4mm head gasket, 0.2mm base, 1.14mm squish
Mazzu economy 57mm rotary crank
GGR hot reed
Stock SI20/20 derestricted and drilled, 52/140, 140AC BE5 130 main, NO filter just frame bellows
SIP Road 2.0 Sport (long twin pipes)
Premix 40:1 Klotz Super Techniplate
23/64 straight cut primary, T5 4th
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Now for the good stuff; I was offered a SIP Performance 1.0 expansion chamber (the JL designed one with the welded silencer) for a great price, as well as a MRP 30mm intake + PHBH28 kit! I had been holding off on going to a SI 24 or 26 for ages now because I knew I would eventually want to do a big reed + sidedraft anyway, and now that I have it I can finally stop blabbing about the "potential" of my Stella and put the proof in the pudding, or whatever the saying is 🤣

Waiting for the last few odds and ends to ship, I put the new pipe on with the stock carb setup to give myself one last SI jetting challenge. In the process, I saw that a few site descriptions for the BGM 177 kit state that the head gasket primarily serves as a spacer for setting port timings to a reasonable spec on a 60mm crank setup, and that it is not intended to be used on a 57mm setup. This explained my inability to get a squish tighter than 1.14mm even on the thinnest base gasket. I removed the head gasket and went to the thickest base gasket I had, a 0.6mm. This resulted in no squish change; only an increase in port duration. This, combined with the new exhaust, allowed me to reach a new top speed of 73mph GPS! Very happy with that result on a SI20 with no venturi, and a case with no port work at all!

Once all my parts arrived, I took off the stock intake and removed the reed block studs. I tapped the threads all the way down into the holes as the MRP manifold's bolts are a little longer than the LML studs. The intake went on without any issues, apart from me having to file down one edge of the reed block top to clear the fan shroud.

For cables, I used the Malossi cable kit sold on SIP. (www.sip-scootershop.com/en/product/cable-kit-carburettor-phb-malossi-22-5781-for-vespa-125-200-px-lusso-t5-rally_94110000). The throttle cable works great, although I am considering a larger throttle cam to quicken up the action a bit.

Here is the baseline jetting I used:
SIP DSRC28 Carb
AV264 atomizer
X2 needle 3rd clip from top
55 pilot
40 slide
135 main

Needle was way too rich there, so I went down to 2nd clip. That cleared things right up and I then cruised at no more than 2/3 throttle until my CHT plateaued, at about 275-285F. I then rolled into WOT in 4th to test the main jet. Pinging after 8-10 seconds so I quickly rolled and clutched in, pulled the choke for a second to richen it up and cool the cyl down. I upjetted to a 138 main for the next run with the same result. Then with a 142 main, it pinged the moment I rolled into WOT after heat soaking at 1/2-2/3 throttle so I limped it home. My hesitation to make a huge jump from the initial 135 main was because I had been informed that it is rare for any setup around my state of tune to need larger than a 138-140 with a PHBH.

I have been consulting with Lee from ThatScooterShop for this whole adventure (actually I bought the pipe and intake set off of him), and he said 142 main is very rich for my setup, hinting towards an air leak. So now I am going to set up a leakdown tester and hope it is an easy fix. However if one of the main seals is the culprit, I am planning to use Malossi's viton seal kit, and use this opportunity to swap to a 60mm P200 crank I acquired last week. While the case is open I will port match it as well; since a couple of months ago I got a crash course on that and ported+trenched a horizontal LC Minarelli case for a friend's CPI GTR50 build. I will save fully porting+trenching the case for a full circle setup in the future as I don't want to increase the crankcase volume too much; the crank I got is a SIP performance rotary valve one.

I love the LML cases for tuned motors. Native reed setup is awesome, even if the cases are relatively fragile.

Are you still on the stock LML reed block? Looks like it in the picture.

Until you get rid of that thing, you're honestly wasting your time with more go-fast parts at this point.

I ran a MMW (similar to the MRP) block with VForce4 reeds with my BGM when I was still on LML cases. That change removes the cocktail straw from the middle of the firehose and will make a huge difference.

And if you haven't done so, don't forget to pick up a 5 or 6mm base spacer to go with the longer rod of the P200 crank. And the BGM likes a tight squish. Spec is 0.8-1.2mm, IIRC. A little stiff to kick over, but it pays off on the road.

Do you know your port timings? I think (but don't know for certain what that pipe calls for) you're going to want to bump them up to something like 129 or 130 TD with that exhaust, so you'll lose power on the slope, but get it back at the peak and also shift the power right, so more RPM's before the red line.

Personally, I found a performance box (SRXL, BBS, Malossi Box) to be a better fit with that build than a tuned pipe, though I didn't try any "modern" tuned pipes with it. That setup would give me a super-wide power band and still do 80 MPH if I was so inclined. Personally, I find that 75 MPH is about all the top speed I want on a vintage Vespa, but I like to be able to get there really fast.

(And I hate that SR2.0 Sport. Restricted exhaust and even more painful than a leftie pipe if removing the rear wheel)

I'm looking forward to more updates on this.

It is hard to see but I am using the MRP Rd350 reed block with cheapo reeds and a stuffer. No i have not measured my port timings but I printed and laminated a degree wheel for when I get around to it.

I didn't know the SR2 sport is restricted over the standard one. Do you know if its possible to derestrict it? I bought it way back when I didn't know much about tuning just because it looked cool and it has served me well these last 4 years.

If I was paying full price on a new pipe I would have gone with a SR3 or maybe one of the Bgm big boxes, but Lee convinced me to be a test mule for a BGM 187 build on a chamber since he hasn't tried that combo yet. Should be fun either way!

This is a very similar set up to what I have. I used the vmc Crono with a 60mm crank and the same reed setup. I also had to grind the block a little to fit past the cooling shroud. I used the sip right side expansion exhaust and a Phbh 30. It's my race track scooter and is by far the fastest large frame I've ever ridde, it's hard to control the front wheel out of turns at the track. The Stella cases are awesome for exotic builds like chandler said. They're cheapish to find and in abundance so I don't feel bad being rough with them. Once you stroke that set up and get the carb right it'll be awesome. I have a phbh30 on my setup and here's my jetting, idk if this helps but do what you want with this info.

Carb phbh30
Av266
X7 3rd clip
55 pilot
45slide
128 main
250 float

How much case porting did you do? Also what ignition? I am still on stock LML ignition but I think my next big purchase will be a SIP Vape with variable timing.

I just matched the cases to the cylinder gasket but the previous owner of the cases had them welded and decked, so I had a bit more room for porting. And settled for either 1mm squish or 1.1mm i think. I used the vape variable ignition but only because its a track bike that only gets ridden at the track. For anything else, id suggest getting the normal vape non variable ignition. I dont have any experience with any other aftermarket ignitions, but the quality of the vape that ive experienced and my friends have experienced as well has been very very good. No reason to want to try anything else.

Small update: I have been wrapped up with some other projects so the Stella has been coming along slowly. I pulled the top end off for some more inspection and it seems to have almost seized at some point. The piston material under the bottom ring at the exhaust port is completely smooth, no texture like the rest of the piston sides. I was told this means it expanded enough to rub on the bore but was not enough to seize, and my quick reaction and good quality oil saved me.

I have almost all the parts for my leakdown tester; everything except the cap and air inlet for the intake manifold. However when I went back out to pull the piston off to soak it in acetone to decarbonize it, when I turned the crank I noticed the parts that were sitting at the bottom of the crankcase were dripping with gear oil... I want to do a leakdown test anyway but I am pretty sure its teardown time. But if this is a standard "gearbox oil sucker" situation why is this the first real evidence of that? Could I have cracked the case at the cush drive spot with a missed shift? (I boogered a 1-2 shift pretty badly on one of the first rips with this setup)