Modern Vespa

That is the exact opposite of what you should be seeing. For now, walk the main jet down so there is no more splutter at WOT in 3rd. That will put you pretty close to where you want to be.

I will also repeat my suggestion that you keep track of your speed (gps only, Stella speedo is just for decoration) as a cross-check. With your setup, you should be doing at least 60 mph on the gps if you're revving alll the way out in 3rd.

Thank you. I will check with GPS. Yes, the stock speedo is crap. It reads about 7mph fast. 60 gps is still a bit scary on this thing. The fastest I have had it is 57mph gps. But I get your point. I have also been taking it easy for break in. But I think that's done by now.

I will make a list of the suggestions I have been given and tick them off. It's not that I ignore them…I sometimes lose track.

You're going to kick yourself when you find the issue.
Take out the main jet or loosen it a turn to make a gap. Then ride. 2nd gear should flood so bad at WOT. This would be a start. Then need to work out why.

Yeah, I'm hoping it's something that jumps right out at me.

I had a closer look at the float bowl cover I took out of the 26/26. I can't tell if the bore is larger, but it has additional holes drilled near the needle hole. The 20/20 and 24/24 only have one. The 26/26 has 3. I replaced the needle on the 26/26 cover and put it back on. Not sure if it makes a difference. I shoulda measured. Anyway, it's back on the carb.

Drill out a small main jet with a large bit. Make it a stupid size that'll be obvious when you pull it out of your jet stash. Scratch out whatever size it is now. I have one I use, when I need a place holder but want to verify I can go to rich.

That's a good idea.

I haven't had a chance to try any new jet combos as the bike just wouldn't start.

Figured out that the plugs I had been using were both carbon tracked on the insulator and were arcing inside. Something I've read about, but never actually seen before. Likely the result of frequent fouling as I fiddled with jets. That kind of abuse takes more thorough cleaning, or even better, a handful of fresh plugs. Started right up with an old plug that was merely old and sooty.

Could have been fighting this awhile, which I'm sure has thrown off jetting and has probably caused some of the problems I was having.

Some things:

My suggestion to tape over the air channel that feeds the slide cutout was to simulate a flat slide. Haven't tried this, but I can imagine punching a hole in it to simulate a different slide.

Did this carb come in a Spaco box?
BGM and Pinasco go through them.
#1 is deburr the needle seat.

Like I mentioned, that 26 is too big for how you ride. Maybe you could shelf that for the P and get a reworked in Europe 24/24?

One of my bikes has an older Spaco. I have three others in the garage. Two are forever needle seats (spring-loaded Viton, BGM carbs) and the other is a two day before flooding. The Spaco out of a Spaco box is a two hour to flood, unless I turn off the tap and let it run, half draining the bowl before killing the engine.

Broke the fuel lever on the two hour last week. Three days and 8 kicks later there was fuel on the floor like yours (no filter, no plug over the mixture screw). Massive flood!

The 140 ac is the ac Whiteone Racing recommended for your setup.

Something like this:

https://www.scooter-center.com/en/carburettor-bgm-pro-faster-flow-dellorto/spaco-si24/24e-vespa-px200-type-with-autolube-bgm8570

The 26/26 has still been a huge improvement over the 20/20. I'm fine with trying a different carb. In the meantime, I think I can make the 26/26 rideable even if it's not perfect.

A question about how I ride…I'm trying to set up an engine that will do a reliable 55mph for long rides. The Si carbs seem require compromise when used on a tuned engine. I would expect that a carb set up for distance riding might be a little rougher for city driving. And a setup that works great between stop lights would not do well for long distance riding. I'm not sure if that's what you mean.

One thing I noticed when I switched to the 50/100 idle jet and be3 was that I tended to be at half throttle or more most of the time. With a leaner idle jet and a be4, I would be at not much beyond 1/4 throttle when cruising.The power would come in as soon as I cracked the throttle.

Since it was pouring buckets again yesterday, I did some arts and crafts. One of the things I hate most about jetting is getting the airbox screw out, where no screwdriver really fits.

Setting aside your apparent fuel flow issues for a moment - I think you can get this thing tuned really nicely for your purposes.

Ray8 seams to be on to something with the smaller throat and modified slide - but I think you can get excellent results with the path your on as well.

I run around on a 28mm carb laden with a sidecar with steel frame. Scoot is fun and easy to ride around town - hill starts and all. Plenty of torque.

On the open road - it makes this joyous angry wasp sound when cruising at 65 - that is pure dopamine joy. More on that in a moment.

I think you may find other variables equally determinative for ride-ability, while still getting benefit of larger carb for open road.
Following based on my experience:

1. Ex port timing. If you are at 180 or below - you can avoid a level of peak-iness that makes in town a constant gear shifting motor screaming uncomfortable mess
2. Same for inlet duration.
3. A good box exhaust or a pipe designed to come in by 5k rpm.

Even with the larger throated carb, these remain powerful levers for adjusting where your power is.

Now - about that cruising dopamine and angry wasp sound.

If you have a target min cruising speed, like say 55mph, I suggest:
Set up gearing to have you about 1000rpm into your power band.

Example - if you use a box exhaust, and the power band is 4K- 6500, and you wanna cruise at 55, gear it so you are around 5500 at 55mph.

This will leave some throttle in your hand for hills, passing, and the inevitable realization that you want to cruise at 60mph (or 65…)

looks like you have a fair amount of open road where u r.
Think you can get a superb result with existing hardware - though hearing may come into play at some point.

Edit: set up for 5000 if box comes in at 4000…

Because, math

That makes sense. I can't remember my timings off hand, but they are tame. I think I am close to 55mph at under 5500 rpm with a lot more to go. I have been so focused on CHT's.

Today I tried a bunch of tried and true jetting combos that ran great but wouldn't keep CHT's down. Ended up with: 50/100, 120AC/BE2/130. It was damn near perfect. Nice in town. Dreamy out on the road. Just a little splutter with the throttle cracked which I don't care about.

Unfortunately, my CHT gauge stopped working and just flashes error, so I have no idea what they were after the last jetting change (from a 125 to a 130).

Other things on the list to try, but the WOT test, making it splutter and flood. I really have to get that done…definitively.

My CHT readings might well be bullshit. Would be nice, because otherwise the way it is now is a keeper.

Here's another video:

The Runleader connector in the tunnel may have disconnected. I had to trim off some of the rubber to get that connection to click-lock. It'll snug and connect, but if it's under any tension it will disconnect from vibration.
The Malossi CHT reads r unless I use a resistor plug.
Has to be either of those two.

Thank you. I will check that out. Probably time for a better gauge.

The issue with the gauge is the wire running to the sensor aft of the connector. I actually had a new gauge that I hooked up to it and got the same error. I'm wondering if I can rewire the sensor while I wait for a new one, which will be the screw in type.

One thing I noticed about the mixer. It changed the throttle position relative to where the power comes in. With the BE3, it comes in at half throttle. With the BE2, it comes in right away. I think this is because the 50/100 pilot was too rich with the BE3, the BE2 leaned it out and the mixture improved low down. BE3=cruising at 1/2 throttle and above. BE2=cruising speeds at low throttle.

I like to think of the mixer as fine tuning after I have established main and pilot, in that order.

Most recent vid has you gurgling rich down low.
Normally, if that far off, I would lean the idle now, at least a few notches, and then focus on my main to dial it in.

Do mean mixture screw adjustments or changing the pilot?

Yes, it's still rich down low when I first open the throttle, but made me happy because it's so much better than with the 20/20 carb. Even with the gurgle noise, what's different is that it actually pulls from down low and clears quickly. With the 20/20, no matter what I did, it was gutless down low and would pull suddenly at 1/2 throttle.

While I'm waiting for a new CHT gauge, I might check temps with an infrared thermometer I have to see how CHT's are doing.

Meant pilot jet.
I think you are at about a 2.0 ratio.
Sounds well beyond any turns of the screw.

As a simple rule, if you turn the screw in and it doesn't respond by picking up idle - you are likely not in range with your pilot jet.

If u like it now - wait til you get closer to right pilot jet.
Gonna feel great.

I believe you. Once I get CHT's down, I will do some fine tuning. I'm hoping to do longer, open road rides without worrying as much about overheating. I would like to ride it to work a couple times this summer; 28 miles of 2 lane state routes with 50-55 speed limit and not much traffic.

At Jack's suggestion, I ordered a 110 AC from SIP via Scooter Mercato. Btw, does anyone know where I could find a 110 air corrector in the states?

In the meantime, I tried to make my own by soldering up a 160 and drilling a new hole by hand. Took me a couple tries. It's hard to be that precise, but by measuring drill bits and welding tip reamers with a micrometer, I was able to drill a hole that was at least 1 mm, but definitely smaller than 1.2.

New CHT sensor ring should arrive today and another CHT gauge with a tap in sensor tomorrow…as well as some loctite 603 for finishing up the 200 engine.

I will also run through the other suggestions, weather permitting.

Trying the 2nd gear WOT test again with a homemade 110 AC 50/100, BE3, 135. Temps got up to 306F but it was a fairly short ride.

https://youtube.com/shorts/eqZSNR40_AE?feature=share

If I look at your numbers - you should be fine.
But…
When I listen I hear rich down low, lean up top.

Not a lot to go on - so I wouldn't bank on that read - but I'm curious - what happens when you go richer with the main.

Just feels like we have never gotten the fuel flow desired somehow.

That's what I'm hearing too. Haven't been able to get it rich enough on top, which was the reason Jack suggested the smaller air corrector. I have a 138 and 140 I could try, but as you mentioned before, the jet size might not be the restriction.

I'm left with testing it with no main jet, or one drilled out impossibly large. I could do a flow rate test, but it seems like the carb is getting enough fuel. I can also try putting on a filter, or taping above the slide.

Beyond that, I'm not sure what else I could do to make the top end richer.

Otherwise, it seems to have more power than I have had the nerve to use. I had it on a state highway yesterday and it seemed to have a lot more than the 55mph I was riding. I was still under 6000 rpm in 4th.

I'm less worried about the rich down low. That should be fairly easy to tune out, once I get the main jet figured out.

I finally got it to splutter. I drilled out an old jet with a 1/16" drill bit which works out to something like a 158 main jet. It absolutely drowned at WOT in second and first and pretty much all the time. I guess that's progress as it's at least getting enough fuel. The biggest jet I have is a 140. I would be surprised if that was not big enough.

That suggestion to tape over the air channel that feeds the cutout under the slide was to provide clues as to why your mid-throttle temps were getting so high.
That cutout has no effect at WOT.

Do you have a moderately steep hill* you can take it to?
A good 100 yard climb would be ideal, so you can reference that with future jetting.
*Free dyno.

Lots of hills here. I will try it.

Ok, so:
- Internal restriction is not an issue. Check.
- Bigger jets will work in this carb.
- Smaller AC would seam a smart move - to keep jets within purchasable range...

When does the 110 AC come in?
How is your collection of jets in the 130's look?

This larger jetting - due to 26mm carb - is new territory for me.
Interesting to watch.

CM:

I guess I assumed that this carb couldn't possible use such big jets.
AC 110 should arrive soon. The one I drilled is pretty close. I have jets; 130, 132, 135, 138, 140. Hoping that will do it. I have gone up to 140 before, but not with the 110 AC. I can always drill some to test using some old jets that are too small to ever use. It's easier than I thought.

Ray8:

Thanks for explaining your suggestion. I get it now. Makes perfect sense.
I'm definitely going to try taping the area above the slide. Currently running the cutout slide that came with the carb. I have a flat slide I can use. Pretty sure it leans out mid range…which is where the the throttle is most of the time when doing long rides on the flats along the lake…or even 1/4 throttle. These rides really bring up the CHT's.

CHT's are a lot better when I ride into the mountains. Lots of high throttle in 3rd gets onto the main and spins up the fan.

Feels like I'm inching closer.

It's been hard to squeeze in rides between the Vermont monsoons.

I tried a 140 and 138 main jet which both sputtered. 135 did not, but feels like it's on the edge, so 135 it is.

Really rich and boggy down low to half throttle until rpm's pick up since switching from a BE2 to BE3.

I tried taping the opening above the slide which didn't seem to have any effects on CHT's. They got to 345* after about 15 minutes of sustained 52mph (indicated 60). Even a stock 150 should be able to hold that speed without getting hot.

Pretty sure I'm rich enough, so I have no idea what's going on with CHT's. The only thing that comes to mind is that they are not accurate. Not sure how else I could measure them to double check. I'm wondering how high I can let them go. The only other things I can think of to try is to retard the timing, increase squish or lower the timings.

test your CHT - get a cast iron skillet in the oven at 350

it holds heat so well you should be able to remove it and touch your sensor to it and get a read

my first thoughts on how to test. the easy ones are freezing and boiling water but you need accurate at higher temp, so this seems like a good idea.

of course you'll need an accurate oven thermometer to check your 350

Thanks, I will try that.

let us know how it goes, I've never tried it but my cast iron holds heat forever after I pull my pork chop out of the oven (sear then bake).

It's a brilliant suggestion honestly. It'll work, I have no doubt.

It is brilliant. Wouldn't have thought of it. I can also double check the pan with my IR gun.

I also have a screw in type sensor that I will install at some point, but I have heard that they read hotter. This surprises me because usually the plug is the hottest point.

The CHT numbers have really been bringing me down. It's what is keeping me from using the bike for it's intended purpose. I don't think a sustained 55 mph is an unreasonable goal for a scooter of this displacement.

I'm tempted to just ride it until CHT's level off…maybe giving myself a cutoff point of 375F. If it pops, it pops. Then I would throw a stock LML top end in it and ride it like I stole it.

Also tempted to shelve this engine, finish up the 200 and throw it in. The old stock top end on it owes me nothing, so whatever happens to it, it's not like blowing up a new kit.

I will test the sensor and retard the timing a couple degrees for now. Sorry for the rant.

CHT isn't very linear. Don't ride over 300F until the jetting is better.
Once the mid splutter has gone the CHT will suddenly read lower.

Yeah, CHT's are a little tough to deal with. Type of sensor, location of the sensor, posted max CHT's that are all over the place...

Oopsclunkthud rides with insane CHT's, but he uses an EGT sensor and relies on that more.
Unfortunately I've lost all my notes regarding the readings (playing with squish/ignition timings) on known rides with an under-plug sensor on the VMC, but the temps were higher with that being above the center of the bowl.

If you want to throw more money into useful gadgets, a $30 endoscope will let you see the piston crown. Stick it down the plug hole and look at the piston wash. Lots of other uses for that tool as well.

Rumor has it the screw type runs 50°F hotter than under the plug type. Makes sense since you install it into the head below the plug so closer to the exhaust. I have tested mine yet, I didn't swap over all the SIP speedo wires when I put the VMC into the 62 Allstate. Once I get a Vespa fork for the 59 Allstate I can swap the engine back over and use the speedo. Stinks having only one fork! Attn: greasy, hit me back about that fork hombre!

I checked the sensor by putting an old cylinder head in the oven at 350 for 15 minutes. It only got to about 250, but both the sensor and IR gun showed the same temps within a few degrees.

I do have an endoscope so I will post a couple of pics of the piston crown.

Photos of the piston: