Modern Vespa

Any water in gas with ethanol will bum you out. That goo is evil.

I'd clean out everything in the fuel supply from the tap to the jets before jet-chasing that possibility.

There's a range where jetting "should" work on a given setup. If it doesn't, it's usually fuel supply or an air leak.

Alright so I got to the tank and carb today.
First I went and got fresh new gasoline, came home and drained the tank. Took a Dremel brass wire brush and the long bendy attachment and ran it through the tank. Got all the gunk out. Sparkling clean. Crammed a bunch of paper towels inside to wipe up the sludgy stuff and then washed it out and dried it. Compressed air and a heat gun for good measure. So that's done.

Went outside to the bike and brought my air compressor hose with me and blasted the fuel line after I disconnected the hose from the carb. Caught the gas in a pile of paper towels then took out the carb to run it through the ultrasonic cleaner.

She's all buttoned up now. But I gotta go get the kids from school then they have ice skating lessons so no testing today. And there's a tropical storm hitting us tonight and tomorrow and maybe Sunday too. So maybe on Monday I'll get back to it.

I'm gonna order richer idle jets but gonna try the same old 120 or 140/BE3/128 and check my plug after cruising around for a little. Reason being that with the same jetting prior the plug was wet and black. Get her nice and warm the cruise for 30-45 seconds at around 1/4 throttle and see what the plug says after I grab the clutch and kill the engine. Now that everything is clean and dry it'll be a more appropriate baseline I think.
Also noticed that I'm still leaking oil out from the hole that feeds into the carb so I torqued to 16.5nm. 13.5-17.5nm is spec and I was down at 13.5 before. That could also have been an air ish leak there. Rest of the engine passes the leak test.

Got everything back together. Went for a ride. Still choppy up to 1/4.
Went home and parked the bike and removed the idle jet.

Soldered up a 50/140 jet and am now just waiting for the 1mm drill bit to arrive to redrill that into a 50/100 jet. Will be here tomorrow night so I should be able to get back at it on Sunday.
What a long frustrating trip it's been.

So much for that idea. Drill bit broke off in the jet.
Ordered a set of /100 idle jets. We shall try again when they arrive from Deutschland

While I wait for the jets to come I put in the richest one I have which is a 2.4 (50/120).

Went out to redo everything jetting wise. Started with 120/X234/140 and walked the main jet down. When I get to the 130 the max rpm in 2nd gear at wot is about 7800. A 128 goes to 8900. Polini box exhaust. Anyone know what their rev limit is? I've been searching but haven't located that info yet.

Any how, I have an issue now with the bike stalling at lights. It does not want to idle below 1300 rpm's. Mix screw I'd have to check where that's at. I wanna say around 3 turns out but not 100% sure.

Don't find your main jet by rev limit on a flat road. It will be lean.
Take it to a hill and find the mj that delivers the most power uphill WOT.
That's your safe mj.

Or get it to splutter on a flat road. The next size or two down will be close to the uphill puller.

Splutter:

The Lemarxon atomisers don't work with the richer AC's. Try the same again with a leaner AC. Going to need the special slide and all the stuff that goes with the atomiser to make that work smooth.

Got that and installed it after the ride. One change at a time type of deal. I didn't get the sleeve though. We will see I guess if it's needed.

55/160 or 52/140
160/X234/whichever mj pulls strongest uphill WOT
Drilled/Cosa or no filter.
LM-L or LM-M slide

The sleeve isn't necessary. It's more a tailor how you want to ride idea.
I have one with and one without. They're different animals.

Sleeve = more torque at low rpm, and easier to dial-in jetting for smooth acceleration from a closed throttle stop with a 24 SI at this level of tune.

Getting there I think!

52/140 4 turns out. I started much further in and kept turning it out until the choppy 1/8 throttle went away. Almost there now. Still a touch of it happening but WAY better now.

150/X234/135 for the main stack, Lemarxon low slide.

Once I got the mix screw to 4 I cruised around for a while and took a plug pic. This is just cruising so 1/4 throttle with some up to 1/2 but not much time spent there.

At least it doesn't stall at lights now. Which is nice and will idle pretty okay between 1000-1200 rpm's.

Great.
Reduce the mj for most uphill power.
I've seen a few setups at this level of tune with Lemarxon parts. 122-130 mj.
I'm good with 125 with and without the sleeve

122 here pulled best from a rolling stop to half throttle, with either a 55/160 or 52/140, but it's a bit lean at WOT.

Max CHT down 40F (with a 125 vs 128-130 previous to using the X234 and LM slide).

Reducing the mj will also lean the idle circuit, so you'll need to adjust the mixture screw and idle speed after any mj change.

Swapped idle jets today but didn't have a chance to test the 48/100 yet. Checked the mix screw and it was 4.5 turns out, so set it back to 2.5 turns for the new richer jet.

We'll see tomorrow how she goes.

Got out today for a 20 mile trip or so. Mostly low throttle riding.

Started with the same main stack but with the 48/100 and the Lemarxon L slide.

Revs hung a bit so I swapped back to the 120/BE3/132 set up.
Better but still a little choppy in the early throttle spots. After 1/8 it cleans up. Plug is lean, but maybe at least it's getting close to right. Mix screw is 3 turns out.

Have a look.

120/BE3/132 is the same jetting as I have in my 210. Are you SURE you don't have an air leak in that thing?

I was when I got it back from Mr. Gick. I'll give it another pressure test tomorrow. It's simple enough to do after all.

Wait, why did you go back to the 120 ac?
You were close. Just had to reduce the mj.

55/160
150-160/X234/125 - 128
LM-L slide

The main stack has nothing to to with closed throttle hanging idle, aside from the mj supplying all fuel to the pilot circuit.
Bigger mj = richer pilot circuit.

Jacks suggestion to go back and try that set up. That first set up ran worse than the 120/BE3/xxx. I'm struggling big time with this. Quite obviously.

I can swap back if needs be and see how that goes.

No air leak. Held 6psi for an hour while I went and got the kids from school.

Had another chance to get this running properly today.

Swapped back and forth between the 2 main stacks with a 55/100 idle.
The 140/X234/130 (worked down from 140, still rich though as it only revs to 8400) was better than the 120/BE3 set up. So I'm gonna stick with that and dial it in.

Next chance I get I'll take a run with the 128mj. Might not be till next week since it's gonna storm all weekend.
Idle jet seems pretty close to perfect at 2.5 turns out. May be a little rich still but I have a 52/100 if I need to swap them.

When I did the mj wot test with a new plug I got no color at all. 40 seconds uphill wot. when I got home after cruising from the wot hill I took a pic of the plug and it looks MUCH better now.
Peep it below.

The effect of the ac is inversely proportional to the mj at 1:3.
From a 160ac to 140 (+20) you should find max power uphill WOT with a mj 6-7 smaller.

Take it to your hill without the cowl, filter and cover to find your rich mj.
Keep stepping down the mj (you've gotta be rich) until you find the one that delivers the most power. No need for plug chops with a decent hill.

If you have a tapered needle, mark it with a Sharpie and at least confirm each mj score-marks smaller to the next to try. Stamped #'s can't be relied on, and can lead to frustration unless compared to each other with a needle.

That LM slide affords you more leeway, in terms of smoothing acceleration from closed throttle via the mixture screw. It has to be played with after any jetting change, including when you put the filter and cover back on.

I'm all lost over here, what carb are you tuning again? X234 doesn't sound like an SI but a 120/BE3 does. What is this thing?

It's one of the Lemarxon atomisers. I'll be also testing them soon with the appropriate slide…

This. I have the slide too. The L one anyways. Hoping I'm good to go with a mj of 125-128. Should be somewhere in there I think.

what does that even mean?

ok a bit of sleuthing says that's a brand name of some fancy new variants of carb parts you can buy through SIP. since when has this stuff existed?

Got out for a short shake down with the 128 mj.

Still some splutter between zero and 1/8 throttle. Not much though. Much more pleasant to ride now.

After that I went real quick around the block with the 125mj and I think that may be the one. I'll have more time tomorrow to mess around with it though.

Positive steps. Thanks a bajillion everyone for all the advice and suggestions. I 100% would not have made it through with out you all.