Modern Vespa

Hello all,

I accidentally bought LML reed cases (thought they were rotary, oil autolube but were reed/no autolube) to replace my massively cracked Vespa PX 150 2005 cases that ate christmas tree gears.

I'm looking to go all in for my current BGM 177/187/193 raised top end. 62mm bell (105mm conrod) crank on the way from our Teutonic friends overseas. I have a JL lefty in stainless steel, as per my More Money Than Brains thread on here.

To keep the beast fed, I was looking at the MRP cnc'ed LML reed block and a Polini or Malossi 30mm carb kit.

So a few questions for the wizards of two stroke joy on the pipe:

1. will a 'regular' reed/30mm carb kit from the Polini/Malossi crowd fit? Is it optimal? I have a dremel. I'd like silky smooth flow, and am wondering about studs/holes on the LML reed cases.

2. If the MRP CNC reed block for LML reed cases is "better", should I go for 30mm manifold inner diameter for 30mm carb? Is it better in any way to have, say, a 34mm manifold for a 30mm carb?

3. I like kits for carbs as they come with the obscure choke attachments etc, and shipping from germany is brutal if I overlook something. Is Polini's PWK a better setup than Malossi's Del knockoff? Meaningfully so?

4. for a 62mm stroked BGM 177 (making it roughly a 193cc?) is 30mm carb a good size? I'm building a street racer that beats everything off the line.

Gigantic non-stock carb setups are new to me. Any help or guidance is appreciated.

I'll have more detail when I'm not on my phone, but I've run a very similar build to yours for a few years now.

I run a Polini PWK34 with VForce4 Reeds in an MMW block. I tried both a PWK28 and PWK 30, but when I did the math (displacement*RPM's vs. Intake area), it said a 33, so I went up a notch and have been generally happy with it.

Check your PM.

30 will be sufficient to feed the beast and with the right gearing make it a stop light eliminator.

if you want to set it to kill and not stun, keep it down geared and go with a 28

flat slides and D slides are going to have better throttle response than round slides for what you're trying to achieve.

Thanks peeps.

Sounds like I won't require the cnc "for lml reed" manifold/reed block. From what I gather from scooterist I will get a good fit from say Polini carb kit.

Can I avoid a fuel pump? I would like to think there would be one in the Polini kits if it was required.

I read chandlerman's thread about a nightmarish keihin setup that steered me back towards kits.

As far as gearing goes, after breaking numerous teeth of numerous gears due to cracked engine cases (oversight on my part; would love to know what previous owner did to this poor scoot), I decided to, and I know this is hard to believe, throw more money at german scooter parts stores.

I had stock 150 gearing which was pretty good. I loved third gear in particular. Could do 90km/h steep uphill. On the questionable vespa speedo of course.

I wanted first gear to do way more/justify its presence, second too, third about the same, and shorter fourth to get the wind resistance/powerband sweet spot, so I bought an alphabet soup of 23/63 straight tooth primary, 12-13-16-19 xmas tree and stock 1/2/3/4 gears. The net result should be taller first and second, third just about the same and closer fourth compared to stock.

I have a screenshot from a gearing calculator site somewhere that shows a super even gear distribution with those numbers punched in for gearing.

Fuel pump not needed for sure. If anything, whenever is time to replace the fuel tab just grab a BGM3030 and that should be sufficient fuel flow.

As far is the gearing, that is going to be very subjective. How often do you go out there and maintain 60-65 mph GPS? The stock speedometer accuracy is crap. I have/had a polini 177 and a Malossi 166, both will do over 65mph gps but to be sincere it is scary to go over 60 mph on the 10" wheels.

It's a good thing you're looking at different gear ratios. Cylinder kits and LML (including the Stella) transmissions are not a good combo. A tall 1st and 2nd with a normal-ish 3rd and a short 4th is a super fun combo. The scooter will always accelerate in just about any condition (hills or wind).

I personally don't like carb kits. They come with a bunch of cables and cable fittings that i can never use. I just buy a carb à la carte. I then buy high quality cables and fitting that i need at a bicycle shop for cheap.

So did you figure out why the christmas tree gear cracked your PX 150 case?

I suspect my cracked cases flexed and broke my xmas gear teeth, rather than the other way around…

And I do have bgm fast flow tap!

Which thread was that? I don't recall it, so now I'm curious if my standards of what's a nightmare are out of alignment with the rest of the world.

34/35 mm carburetors ??

5th post down iirc

Oh, yeah. That was mostly that particular carb combined with it being my first side draft adventure.

I've come a long way since then, but two things I learned still apply:
1) If you run a big reed block, you won't get full use of the fuel tank without a pump
2) Don't try to "make it work" with the wrong parts or you'll wind up frustrated and disappointed

I wouldn't let that particular experience put you off trying it, but it may certainly be more work than you're really interested in.

Also, the dellorto self-regulating fuel pump is what I use now, and it's been awesome. Just plugged it in and went on with my life. Other than having to plumb the pulse line into the case (or, in my case, reed block), it was literally just "cut the fuel line, plug it in, tighten hose clamps."

Got a photo of how you plumbed the vacuum line into Reed block?

I do, but it's not very interesting.

It's a 1/8" ID brass 90 degree nipple that's into a 1/8" NPT hole that I drilled & tapped into the block.

Hadn't thought about doing it into the manifold. Been formalizing a build of my own with pwk35 carb and was a bit intimidated to tap a vacuum hole into cases. This option is much preferred as it leaves cases original.

Honestly, I just forgot to re-drill & tap the new cases when I rebuilt the motor, so it was that or split the cases (again). It's working well, though.