Modern Vespa

Hi guys,

I've fitted a VMC cast iron cylinder to my Sprint 150 veloce and need some help on jetting and running in.

I've give up with the S20 carb and fitted a 24mm. My stack - 160/BE3/126 and 55/160 idle, 2.5 turns out on the mix. It starts great and ticks over well. Does this stack look ok, Is there anything else I need to do? Any advice on setting this baby would be appreciated.

Thanks all.

Do you have an exhaust box or expansion chamber exhaust? I think your numbers are spot on. That is what I run on my 150 scooters with cylinder kits. I go between 122-125 main jet but everything else the same as yours. I do run either exhaust boxes or expansion chambers back and forth.

Seems like a good starting point. My PX with a bolt on Malossi, 24/24, overdrive and box exhaust is at a 160,BE4, 130. The 3 port Veloce motor should be pretty dang close

If you changed the AC to 120 and pilot to 55/120, I think it would go a lot faster and wear out slower.

I'm running a SIP Road 2.

When i was on the Super G, 24/24 carb and bigbox. I was fine with idle 45-140 and AC140-BE3-MJ122-125. It was a Nice setup.

My jetting adventures with Super G starts from third page here. Maybe you can find something helpful.

In the end my jetting is:
AC 120
BE 3
main jet 125 or 128(depends on situation)
idle jett 55/100

Thanks for your help guys I've got some more jets etc and I'm ready to start playing around to fine tune the carb. One thing have come to mind thought, do I need a fast flow fuel tap with this setup?

I vote for FF tap. Did you drilled fuel passage in carb to 2.5 mm ?

No it as stock si24

I replaced the tap about 18 months ago but can't remember if it was fast flow. How would I check?

If it is SIP or OMG(BGM is same) - it will have lettering on the back. Then maybe worth to do

Faster flow won't have a breather tube.

Roland,

Please post your elevation above sea level. If it's anywhere near my elevation of 1,100 feet above sea level I may use your jetting as a starting point for my project.

Hec

Average is 574 feet.

Thank you! That helps!

Hec

What kind of riding do you plan to do when you're done with your bike?

I'm going to do town work and weekend ride outs with no motorways.

Hi guys, I think I'm getting close to the sweet spot, but not sure if I'm a little lean. Drilled air filter, my stack is now - 140/BE4/122 main jet with a 55/160 idle, 2.5 turns out on the mix. It starts great and ticks over well and goes like stink. I'm unsure if I should be using a BE4 or should I stick to the BE3, does this stack look ok, Is there anything else I need to do? Any advice on setting would be appreciated.

I've attached a couple of pics of my spark after a good run.

Cheers in advance.

To test the main jet is near correct, hold the throttle wide open on the stand. How high does it rev? Fit a 128 jet, how high does it rev now? If the 128 revs at least 1k less, then the 122 is about right.
The atomiser is best decided with throttle response. Ride around at 30/35mph, open the throttle a touch. Did it pull, bog, cough, splutter? If it didn't immediately pull it needs attention.

I can't WOT it as I'm running it in, only done 50miles when I run at a steady 40 is pulls nicely if I open up the throttle and starts to slow if I pul the choke out.

You've done 50 miles. You're allowed to open to wot on the stand a couple of times.

I'm now running with a 140 BE3 MJ124 with drilled air filter and a 55 idle. Runs great pulls well, but only niggle is that the top end seems to max out around 55 and loses power up hills. Is this normal, or am I asking too much?

I'd say theres more to come, my vmc on a px 125 went over 60 before I bottled out/ran out of road.
That was on ac160 be3 mj128 and a 55/160 idle but I felt that jetting was lean. Since adding the sidecar, I've moved the jetting to Ac120 be3 mj128 52/100 pilot and I have more power. Still some tweaking to go I feel. (Going to try a 125mj next)
If your not spluttering top end , maybe an increase in mj might be a good 1st move?

Thanks Andy I'll give it a try, keep me posted how you get on.

Will do, to give you an idea that jetting is getting the sidecar rig up to 50mph. also bear in mind I'm no expert so always jet rich and come down, its cheaper that way

Tried the 125 jet, lost power top end so back to the 128.
Trying a be4, we'll see how that goes

Getting there then. I've not been out, too much rain. When it clears I'm gonna try a 38 mj and take it from there 👍

I've been dodging the rain as well, had it mot'd yesterday, managed to do that between showers

After some faffing about I've settled on Ac140, be4,Mj 130, 52/100 idle.
Just a smidge of splutter in mid range but pulls well and is exceeding 50mph with a sidecar

Change the AC to 120 drop the MJ to 125 and it will be even better. The Spluttering in the middle, even if bearable, will be annoying, cause spooge and waste fuel.

Thanks for the suggestion Jack but at one stage I had it on a 125mj along with a 120ac and a be3 and lost some top end (pulling a sidecar by the way).
But I'll give your idea a go (nothing to loose) unless you think otherwise.

Just a thought, jets are by BGM, maybe theyre coming up on the small side?

I think Ray just posted in another thread with a chart of BGM jets actual measurements and their 125 is actually a 124. I think.

He did. In the project 61 thread

Can't mix and match your jets. The sizes are nearly guaranteed incremental, when they are all from one box set.

Start with the 130MJ you have. When too rich, WOT in gear increases rpm slowly, until it suddenly hits a wall of splutter. Drop a jet size or two and WOT runs clean. If this exact scenario doesn't happen it wasn't rich enough in the first place.

Thanks for that info, helpful

Thanks Jack Will try that out on Thursday ( work getting in the way tomorrow) and let you know how it goes.

Apologies to the op looks like I've hjacked the thread a little

Jack you are a genius, dont know how you do it, but your suggestion (Ac120 be4 mj125 52/100 idle) is brilliant.
Just been out for a ride and the engine performs the best it ever has, power everywhere, pulls like a train, no splutter, tickover drops like a stone.
So a huge thank you sir.

Happy you're happy. That's the end of the beginning.

Gearing for Malossi Sport 221 (Post 2660469)

Written this a few times, link is the last time. Now you're at set up stage 1