Modern Vespa

Hi, sorry another jetting query.

Best I have got is 40 slide, 55P, 1 1/2 mixture, AV266, X13 top clip and 142 Main. Bogging low down which is ok then smooth throughout from 1/4 throttle. But this is lean at 55 mph cruising as I use a CHT and see spikes in temp, then returns at lower revs.

Would 2 or 2 1/2 turns out on the mixture and 2nd clip on the needle be rich enough for cruising?

Tried AV264 and X2 but bogs everywhere apart from WOT.

Spec:
Old 08 210
PM Head
60mm crank 1.5 head gasket
1.3 Squish
9ES plug
Scorpion LH pipe
28 PHBH with bellow
SIP 2 Fast flow + Mikuni pump + 350 FV
BGM stator
BGM coil
16.5 static
PK flywheel

Assuming it's a rotary valve setup?

Assuming the engine is in good condition. First thing to be sure of is the float level. 24mm on a phbh. If this is not within 1mm jetting goes weird.

Next, check 142 main jet is the biggest it will take and still rev out at WOT.

If these two steps are not right anything to do with needles or pilots will not play ball.

Trying to understand your needle setting, if your using top clip position that is as lean as possible. Further needle is into jet in carburetor leaner you will be. As you lift needle up, raising it up and out of jet richer it gets.

Well, I learnt something today!

Do you have other needles to try?
Get one with a fatter end & longer taper... something like that

Here is the info... have fun goin down that rabbithole (or needle pit)
https://www.thisoldtractor.com/dellorto_slide_needle_specifications_for__phbh_motorcycle_carburetors_-x_slides-.html

Just in case that wasn't enough to give you a headache...

https://www.lambrettaspares.com/pages/downloads/TECH%20SITE%20DELLORTO%20NEEDLES.pdf


So, where (which revs) do you want MORE FUEL?


If you are LEAN at WOT, then change to 2nd or 3rd clip... that will RAISE the needle, which will mean there is MORE FUEL earlier & at WOT (as needle is no longer restricting the flow).


My initial comments, without reading issue correctly....
X2
X25
X47 ? Probably too long.

or

Use a SMALLER MAIN jet & go to a 2.48 shaft.



Also, what colour FLOAT does it have;
White or Black? (Different weight, from memory black is heavier)
To you have Black or Clear bowl? (They're different heights.)
Is the seat a 200 or 250? Does it have a SPRING.?


Once you have rammed yourself so far down that needle hole that you can see a tiny circle of daylight....... then PRINT the following, grab a highlighter & a few coloured pens & read it, a few times, it will eventually start to make sense...
http://www.iwt.com.au/private/Dellorto%20manual.pdf

Then, when you have tried a dozen different needles, have every imaginable spare part & are STILL having problems.... check the timing, as most fuel problems are electrical!

And IF you are still bored & decide you want to modify crap even more, grab the needle you kinda liked, except for a certain part of the rev range where it was still too lean... put it in a drill... get some 800grit sandpaper, spin that needle & hand customise that needle to suit your specific needs, finish it off with 2000grit so it's nice n smooth, try that...l then realise it's an issue with the CDI / variable ignition / electrics / loose spark-plug lead etc.


Ohh, i just saw this... "Mikuni pump"

Well, by now you have read up & KNOW the answer... there are 2 main components you need to check........ read up & understand sections 3.2.1 & 3.2.2.

Thanks for your responses, yes it is becoming a headache and an obsession! Its a rotary valve with a white float and black bowl. I run the pump from the back of the carb (not manifold) with a short tube and return pipe with a 400 FV.

Engine rebuilt this year, timing has been tripled checked and CDI/stator/Plug are new.

I have X2 and X7 needles, multiple pilots and mains with AS266/68, AV262/264/266/268.

Tried the X2 with all the AVs and bogged throughout, with the X13 it feels the best of the 3 and the 142 main is the largest with this set up and AV266 before it splutters.

50-55 is where the heat builds ~380f, either side really good temp at ~250f. I had the mixture screw in at 1 1/2 turns, changing this to 2 1/2 out would this help?

You shouldn't be anywhere near 142 for a main…

This should work, because I've had similar setup to yours:

55 1,1/4 turns out
As264
X13 second clip from top
130 main
300 float valve

You shouldn't need any more or less than that… rotary valve is super forgiving with the phbh

You don't need a fuel pump with a phbh and rotary valve… the fuel bowl is large enough.

Only time it's worth using is a TM/TMX carb and a reed valve setup

If it doesn't run well for you, you have other problems and haven't set it up correctly.

Most likely a leaky intake manifold or clutch side seal

A leak down test is the way to go… eliminate the guessing

Thanks 108 for the info.

Just put a reinforced clutch basket on but haven't been back out on it yet so hopefully if there was a leak its now ok and I took the manifold a couple of weeks ago so that looks fine also but will check around. I did have a TM30 but it kept hitting the frame, the PHBH is a bit shorter.

When you say AS, did you mean AV as mine is a 28mm perhaps yours is a 30mm?


After just getting back into scooters its trying to remember what and how I did things and I had forgot how much fiddling we actually did back in the day, a fireblade is so much easier

Nope an AS atomiser… a taller atomiser…

You need the needle to be as rich as possible and to kick in a little later.

Give the needle "width" and slide time to do it's thing.

Yeah the TM will hit the frame and the fuel economy on it sucks ass

If these two steps are not done well, every other adjustment is irrelevant and you'll either be adjusting needles for years or until it blows.

"Would 2 or 2 1/2 turns out on the mixture and 2nd clip on the needle be rich enough for cruising?"
why not trying it out straight away

also try a x2 with different C value

btw
as is for street
av is for race (richer at bottom end)

as simply noted in the dellorto manuals