Modern Vespa

I did see that you recommend going with a 100AC on the previous page. But that was back when i had the 24/24G carb still in place. So a 100AC is still recommend for the 24/24E carb as well? To buy a 100AC it's going to cost me just over $50. Reason being that it isn't sold separately and i have to buy it in a kit.

https://www.sip-scootershop.com/en/product/main-air-correction-jet-set-kmt-100-140_KM110150

Lemme check to see if i have a different 24/24E on my shelf that has the angled outlet bar. Just as a reminder, the 24/24G carb that i previously has installed had the angled outlet bar, and the engine would still rev to the moon (but i didn't drill the fuel inlet hole though).

KMT sell them directly in singles.
https://www.kmtproducts.co.uk/?cat=DELLORTO-TYPE-JETS&subcat=D22-Air-Correction-Jet--Dellorto-Type-5827-&page_id=7&category_id=1&sub_category_id=14&menu_id=

By taking the main jet out it proves it needs to be richer, regardless of carb type, more fuel, less air, same difference at wot.

Thanks for that link. It's still going to cost right about $30 and that's if i don't get pinched with any sort of customs fees.

To get you started just make one out of a 160

Drop some solder in a 160 and drill it 1mm…

I did this, and also made a 55/100 out of a 55/160

Oh, 120 isn't 1.2mm, it's smaller, just fyi…

Well, for what it's worth:
Anything larger than about a 125, and your other carb, in my experience…
Would behave just like you haven't changed to a bigger jet.

So you may not really have been testing anything if it wasn't drilled.
You will get about a 10 point drop when you'd drill out the carb hole. Maybe 12.

Air filter?
If it's drilled out and you replace it with a non-drilled filter it will be close to a 100ac.
I've seen hundreds of setups at this level of tune. Close to none with a 100ac. Sounds nuts to me.
The 120 initiates the circuit before cutout in the slide initiates. Not fun on a stop and go bike.

Take it to a hill.
No cowl, no filter.
Whichever mj pulls the strongest WOT is the rich/safe mj-ac combination.
Helps if you have enough bits to able to put main stacks together and ride with them in your pocket.

160ac undrilled filter.
150ac, one 5mm hole above the main stack. Air hole above the pilot jet doesn't help.
140ac no filter/venturi/new VMC airbox.

+1

Never been on a 120ac or below on any engine.

All malossi 210/221 I jetted are mostly on 160.

Makes me slightly perplex to see anything lower to be honest.

Huh?... little bits in my pocket? Don't spread that rumor around...even if it is true.


OK, i just did some more testing a couple minutes ago hand here are my results-
I did not change any of the jetting from my previous test. What i did do is swap out the 24/24E carb that has the three small holes in the brass fuel bar, over to a different 24/24E carb that has the standard single large brass opening that's cut at an angle. For the sake of having a base line test, i swapped the same exact jets into this second carb. I also drill out the fuel passage to 2.2mm.

FYI, all the air filters that i have on all my scooter have the heart drilled out on them, including on this scooter as well (air filter was installed, but the carb box top was not).


I didn't go on any test rides. I did my testing once again while the scooter was on the centerstand. I used masking tape on my throttle tube to mark out idle, 1/4, 1/2, 3/4, and WOT throttle. Here are my results (with a Sito+ exhaust)-


throttle / RPM
idle / 1800
1/4 / 8100
1/2 / 8200
3/4 / 8300-8500ish
WOT / 8700

It revs up to 8000 pretty quick at 1/4 throttle, but is a but starts to get a little bit gurgly at 8100rpm (1/2 throttle) and stays that way until 3/4 throttle. At WOT the rpm drops to about 7900, but then slowly revs up to around 8700+. There was a spot somewhere mid range (around 1/2 throttle) that it reved all the way up to 10k rpm, but i had to really search for that sweet spot. And i could only find that 10k rpm spot a couple times. There really wasn't much of a change throughout the whole rev range. At WOT it just sounded a bit more blubbery than it did in the mid range.

Whodat!

Congratulations- you've achieved way too rich a main.

Stand has ZERO load, so multiply by 10 and subtract 4 or 5.
It's all science.

This thing should run properly god awful when u take it out.
(Except at 1/4 throttle).

So get out on ur fave stretch and feel the awfulness.
Then start moving down main jet sizes until it starts to run good.
Then move down one more and feel the joy.

Once it starts to improve, u can also use ur cht to decide how lean to go.
One thing to remember.
U r taking head CHT now.
Ur old 315 under plug is now 365.

If the numbers are freaking u out, put an under plug sender on until u get tuned in. Then swap back to head read so u can correlate the two.

I'm now tempted to drill out the fuel passage on the 24/24 T5 carb that i originally had installed and see if i have the same results.

What i find peculiar is that on all my other scooters is that the RPM has a more gradual increase as the throttle opens. Currently when i open up my throttle a 1/4 of the way, the rpm jumps pretty much up to the max 8000rpm. None of my other 200 engines do that.

And i did temporarily install an under the plug CHT sensor for the initial jetting and running in. I might just keep in in place until it breaks, then plug in the other sensor?

Pilot jet is a bit too small. MJ is just a couple of jets too big. If you go back to the T5 carb with the smaller AC it will end up better.

Now I do have a KMT pilot jet kit. Are there ones that you'd recommend me to start out with (on the E carb)?

Take it for a short ride exactly as it is on the E carb. How is it cruising at 1/4 throttle, hot, rough? How high does that main rev in 2nd flat out?
What's in the jet kit?

my jets in no particular order-
68-160
65-160
60-160
58-160
55-160
52-140
50-120
55-100

And as a reminder 52/140 is currently installed.

My vote - throw that 55/160 in there.
It will be in the ball park.
Some ratio around 3.1 - give or take a few points either way - is likely going to be a winner.

You have a pretty lean idle jet in there based on my experiance.

I currently have a 52/140 idle. Isn't a 55/160 leaner?

Sorry - inability to divide...
Somehow got 3.8
¯\_(ツ)_/¯

Wiki [D] Guide: SI Jetting Chart + How to Tune an SI Carb

Did you get a chance to take it for a ride yet?
Until the main jet is near, working on the pilot is not accurate (SI carb only). It will need doing again but to get it near for now, this is the easiest way. Idle screw all the way in at max, mixture 4 turns out. Keep fitting a bigger pilot jet until under 1600 rpm. Set the mixture, reduce the idle.

No test ride just yet. We've had rain, rain, rain, but it's supposed to clear up later this week. So in a couple more days i'll take it for a spin.

I don't quite understand, "idle screw all the way in at max". As in adjust the screw until the rpm is really, really high?

So much rain here too. Have 2 test rides waiting for ages. It was dry here when I was away. Typical.
Really really high means really really lean. Need the mix screw 4 turns out at maximum rich. If this can't keep the rpm down, then the pilot is too lean.

Who Dat!
Just in case what Jack's telling you is a little unclear - don't fret!
I am a certified translator of Jack's insights - honed but not shaped like wizard sleeves...
Trust me - just don't ask me to divide.

Salient points to consider as the rain subsides: 1. Best to work on main first before moving to idle jet
2. That said (British love to use that term before they say the complete opposite. IK, I'm married to one. 🙂 )
A. Turn your idle screw all the way in (makes idle super fast) and your mixture screw 4 full turns out (makes idle mix super rich).
B. Open the barn door cause it's gonna smoke like Cheech and Chong (I added that bit 🙂 ).
If your idle remains above 1600RPM - then fit a richer pilot jet.

Background - the idea here is that you are making your idle pig rich.
If your idle remains above 1600 RPM with the mixture screw turned a full 4 turns out - then its more like you are just regular old cat rich, and it might be a hairless cat - so that's no good.

You just keep trading up to the next richer idle jet until your idle (with mixture screw out 4 turns and idle screw wound all the way in) refuses to go above 1600 RPM no matter how far you turned the idle screw in. Bob's your uncle!

Caveat Emptor - which I think is Latin - but it sounds like something a British person would say - this is a decent way to get in the ballpark football pitch - until you get really close with your main - then you can revisit the idle afterwards and tweak, or twerk. What ever suits your fancy my good man.

Bonus round: allow me to add some highlighting verbiage .
IF IT IDLES Really really high, WHEN ITS $ TURNS OUT, AND THE IDLE SCREW IS SET TO MAX IDLE, IT means ITS really really lean[/u]

Thank you for the interpretation Ned. And regarding the 4 turns on the mixer screw...is that for the fine or course thread version? I'll have to double check, but i think i might have a fine TPI on my screw.

Ah that's one for me; technical not anglophile interpretation. Thread pitch - doesn't matter, either. Once 4 turns out on a fine thread, it's max rich. 4 turns out on a course thread, is open more but was already max by 3 turns. This max situation continues until the screw falls out. At which point it's not max anymore.

If it's not Max, it could be Chuck?

If it's a KMT that would be my vote too.

The 52/140 is richer in the equation, but it isn't richer past closed throttle to mid rpm.

Fuel hole size, the same as the main stack:
Find the one that can pull from a rolling 2nd smoothly uphill with the mixture screw adjusted anywhere between 1 and 5 turns out -- takes a long time
That will be rich enough for gear breaking, from my anecdotal experiences of many.

I have both a Dellorto and KMT 55/160. I can only assume that they have a slightly different jetting from each other (since they're from different manufacturers). Isn't 1/4 throttle still considered mid rpm? Because my rpm is up around 8k at that point.

Is there any chance some of your jets aren't what they say they are? I've been checking mine and found some are off. I had this problem when working on VWs. Before I realized the jets lied the death blade got close to being put into service.

KMT 55/160 would be like a Dellorto 58/160 if they made one.

1/4 is mid rpm on my Allstate. It's an important area to check, since the main stack hasn't initiated and the mixture screw influence has tapered off.
I plug chop there and WOT.
When you connect the new CHT sensor get ready for more clues. I jet the pilot to hold or cool while gear braking/rolling off a run to closed throttle. This can't be seen with an under plug sensor. Also expect your CHT to spike in the cold (runs leaner) vs an under plug that's exposed to cooler air.

No-load jetting on the stand is confusing me. I can see the clues provided(!) but that's not the road. Caveat, I couldn't try this anyway. Neighbors hate me just enough to not throw rocks yet.

For example, I'm jetting for two-up 300lbs. Runs rich riding alone. Runs great alone in the winter. So many on-road your ride variables, on top of all the other variables

What I'd try:
140/BE3/135 mj down (drilled-out heart). If 135 isn't too rich something else is going on.
58/160 first. If that isn't too rich something else is going on.
Good luck!

Absolutely, to the point they all need to checked -- at least to each other with a tapered needle.

Btw pretty much everything that applies to the Weber carb applies to the SI.

Weather has been beautiful, but i haven't made the time for any test rides just yet. Yes i'm still trying to sort out my jetting, BUT i just finally noticed that the idle jet numbers coincide with the air corrector numbers (yes, after all these years). Such as AC100 and 55/100, AC120 and 50/120, AC140 and 52/140, and AC160 and 55/160. SO what's up with that? Is the idle jet # supposed to match up with a particular AC#? Such as a 55/100 with an AC100?

Still trying to wrap my head around the 190/BE4, 50/120 on the 10hp P200's

Not sure about supposed to, but it's less frustrating to have the ac's close to each other.
140ac/drilled out heart is close enough to a 160 for your 55-58/160's.

Have you compared your brand-mixed mj's and ac's to each other with a needle?

I only had a couple of the mixed brand MJ's. The holes were visually a different size so i double checked them with a needle to confirm. That was many years ago when that happened and i threw those jets in the garage so that they wouldn't ever get mixed up with my dellorto brand.

I haven't checked how the KMT idle jets with the same number as the dellorto idle jets compare.

I currently only have dellorto brand AC's.

I just rode with both to find out. There's an afr graph comparison out there I can't find.

Took two weeks to go through my bits with $$ reamer and cheapo micro drill bit sets. Pretty wild. My IDK 140 AC was a 150. A 128mj can be 122.

The atomizer and idle jets are more complicated, but the others can be corrected/modified/re-labeled fairly easily.

Btw you're in the range for the Lemarxon sleeve along with his other bits.
Night and day.

I finally made some time this evening to mess around with the jetting some more. The engine sounds rich throughout the whole rev range while it's on the centerstand. I went for broke and tossed in the richest idle jet that i had. Current jetting is-

AC140/BE3/130MJ
idle 50/120
Sito+ exhaust

I did a shorter 8 mile test ride though the hills (and wouldn't you know it, there were more deer out near the shoulder of the road). The temp sensor is currently located under the plug and my temps stayed below 265F. I'm guessing that it needs to be more lean, but as is i don't foresee it seizing on me. I'm kinda wondering if i can get away with reinstalling the JL Right pipe that i have, but i think i want to get the engine broken in first with the Sito+ (just to have an extra safety buffer).

Good sign it didn't seize up. I would be happier if that was 55/120 or bigger. What main jet size was unridable, spluttering so much it won't rev out?