Modern Vespa

Hi guys, I'm in the process of rebuilding my 150 sprint veloce and need some advice. I'm looking at fitting a 177 DR cylinder and changing the crank, which looks worse for wear. I'm stumped on what crank to fit, race, normal or long stroke. I also have a S20 carb and a SIP road pipe, and a SIP vape ignition on it. I'm not looking at turning it into a racer, I just want a little bit more grunt for when I take a passenger on it, or meet those beloved hills.

All advice is appreciated 😀

Definitely get a 60mm crank. Definitely don't get a DR kit. Modern technology VMC or BGM kits are better suited to your requirements.

Why VMC? Will a 60 crank change the engine timer.

Engine timing is set based on the SIP vape kit, will the 60 crank change that?

I would go with a BGM 177 bolted on. I think the VMC transfers will be larger than your gasket surface, but I could be wrong here.

Honestly, if you want to keep it simple (KISS), a 57mm crankshaft will serve you well. Your ignition timing will need to be changed from stock to something like 18 btdc for either BGM or VMC . You really need a 24mm carb for either cylinder but a 20 would work for the short time.


You could bolt on a DR cylinder without changing timing, I guess. It's such a relic and pathetic, but would get you down the road. I don't advise it.

Yes, the ignition timing will change, very slightly. If looking at stock setting of 22 degrees BTDC for a Sprint with a 57mm crank, The distance of the piston BTDC will be 2.62mm. With a 60mm crank, this changes to 2.79mm at 22 degrees. Therefore, to get the original firing distance of the piston from TDC of 2.62mm, the timing needs to change to 21.3 degrees BTDC. I used this calculator.

Port timings will change also and these will have a larger effect on the 'personality' of the motor. You can alter the port timings by raising, or lowering the cylinder with packers/spacer gaskets to get more torque for low end, or a higher revving motor and more top end power, or even something in between.

Some crank reading HERE.

Hope this helps.

Seems that advice used to be to put a 1.5 mm spacer under the barrel to make up for the difference between a 57 and 60mm crank.

But measuring and setting up port timings turns out to not be all that difficult and there are lots of people who can guide you through it. The 60mm crank usually crank gives you more wiggle room to set the timings using shims or spacers without the need for machining stuff.

I now running VMC Super G after DR. Absolutely night and day. Much more fun on VMC even with 57mm crank and p'n'p cylinder.

What carburettor are you using for your VMC? What unit are you running the cylinder on?

It is P150X, ports not matched, Mazzucchelli racing crankshaft 57mm stroke, SI 24/24 with drilled fuel passage to 2.5mm, original old Piaggio air filter heart shape drilled, Polini carb case cover, SIP Touren flywheel 1.6 kg, Polini Box exhaust, 23/68 primary gear(still thinking about do I really need longer ratio with short 4th gear and seems like not)

Why not just slap on a cylinder kit and call it a day? I put a few cylinder kits and did little to the engine. This year I got a new Malossi 177cc for $249 and it flies compare to the stock cylinder. All I have is just an exhaust box. If You don't have to change the crankshaft is better to not touch it (in my humble opinion).

I would only would to the crankshaft is I really have to split the cases for other stuff.

I've only opened up the engine to change the cruciform. I just thought about and noticed the crank had a bashing so thought I'd sort that whilst there. After hearing all the advice I think I'm just going the change the crankshaft and pop on a VMC 177 cylinder. I've already got a SIP box on it and if the carb needs upgrading to a 24 on will deal with that then. Just gonna see how it goes.

Thanks for advice.

I've now got a VMC Super G with an centre plug and I've just started a full engine overall. Any advice on which spark plug to use?

NGK B9ES or NGK B8ES or smth. similar.

I have rebuilt my engine with a 177 Vmc and kept the original crankshaft and SI 20 20 carburettor and a SIP Road 2. I have started by running a 132 main jet and a 52 idle jet. It starts and ticks over a dream, but when I ride it rides like a bag of shit once I get going. Have you any advice if I'm way off the mark with my jetting.

I can only say what worked for me. I installed a BGM 177 kit on my 1979 PX125 and found that the BGM recommended jetting was far too rich. Now I will add that I did not do any modifications other than the kit, a matching BGM crankshaft and a Pollini exhaust, but I found that in the end the only jetting combination that worked well on my SI20 carb was the standard PX200 jetting:- 160/BE3/118 and 55/160.

I took her on a 60km ride yesterday and, if anything, she is still slightly rich but I'll live with that for the moment.

She starts easily, runs well and idles. One more thing, after struggling with so many different jets, I had to replace the spark plug. The earlier rich jetting had totally fouled the 1st post install plug within 40 kms...

Looking at my notes- similar setups show mains from 120-130, with the hardest riders using a 130. Do you have anything smaller than a 132? Swap it and go for a short, easy ride. That way you can confirm it's a fuel issue and not electrical. Eventually you want to settle into the best performance, but still favoring the rich side.

Thanks, I've got a jet kit from 118 to 136. I started with a 132 because I'm just a bit worried about a siezure.

What's the rest of the jetting? Which filter?

It's a 160/B23 132 Main with a 52-155 Idle

152-160 Idle

It's jetted way too rich. Take a look at your spark plug, it's probably an oily mess.

I'd put a 140AC in and drop the main to 120.

1. Reading between the lines, it sounds like you have a 160 air corrector, a BE3 mixer tube (a/k/a emulsifier, a/k/a atomizer), and a 55/160 idle jet (there is no 52/160 unless you make one yourself). Pretty standard stuff.

2. We need to know where in the throttle range it rides like a bag of shit: 0-1/4. 1/4-1/2, 1/2-3/4, 3/4-4/4. We also need to know if it rides like a bag of shit when it is under load (rolling the throttle open—even just a little) or not (backing off the throttle—even just a little).

3. The combination of a 160 air corrector and a 132 main jet surely is too rich for your set up. If you stay with a 160 air corrector, your main jet probably should be somewhere in the range between 115 and 120. Try a 120 and see if it splutters at wide open throttle in 3rd gear.

Yeah, that BGM recommendation is for 24 carbs.
It's rare to see a 177/Polini box setup with a 20.

Thanks guys, I will try a smaller jet at the weekend and let you know how it goes. 👍

As said this jetting doesn't work for your carb. Bottom end will be way too rich and high rpm way too lean. That does mean at one throttle position somewhere around 5000rpm it will be perfect but either side of that spluttery or piston wearing.

Whatever air filter or vortex you want to run, keep it the same and refit every jet change. They have an affect on jetting.

With these carbs the main jet stack has to be set before the pilot. Begin with AC140/BE5/132 and hopefully, wide open in 2nd gear won't rev out and splutters badly. Then reduce the main jet until it does rev out.

Hi guys, I've give up with the S20 carb and fitted a 24mm. 160/BE3/122 and 55/160 idle, 2.5 turns out on the mix. It starts great and runs well and only a little boggy. Should I run it in on the 122 main or increase it a little whilst running in? Is there anything else I need to do?

Cheers

160 AC with a 122 main seems really lean for that setup.

I'd have expected more like a 140 AC with a 125-130 main and probably a richer atomizer as well. Maybe not a full BE4, but a BE1 or 5, at least.

Remember, a too-lean motor will seem like it's running great, right up until the point it doesn't.