Modern Vespa

Hi every one.
As some of you already know, i am in the beginning of rebuilding a 1969 Super.
The original carb is 20-15.
My fear is that it won't be good enough, i intend to add a sidecar.
Any one think i need to put a better/bigger carb?
If yes, which should I put?
Thanks!

Generally, on any older bike that came with a 20/15 or a 20/17 i replace with a 20/20.

If it's a 125, i usually minimum bolt on a 150 top end.


While this isn't stock, it is more along the lines of 'later spec stock', essentually building it into the equivement of a later model.

thanks Rob.

so you say just to put a PX150 carb and it would be better fuel flow?

can it do something bad to the motor beside drinking more fuel? like a high wear to some parts?
thanks again.

In theory, hyes. But no more than a px 150 would

Youj'll pick up a little performance, you're gaining a bit under double the mixtgure into the bike.

I replaced the carb on my Super with a 20/20. I installed a 55/160 idle, 160/BE3/100 stack and I think the starter jet is 60. Noticeable improvement over the 20/15, but I also milled in a third port and it has a three port cylinder, 150cc. Also installed a P150 stock pipe. So, it's worth the upgrade, but I don't think it is going to be enough to pull a sidecar very well. Do the upgrade first before putting on the hack, you may have to change some gearing to pull it well enough.

Was hoping you'd weigh in T. Did you ever apples-to-apples the 20/15 and the 20/20 to see how much difference the carb alone made?

It looks like I am about to test it...

But if any one did try to change only the carb and can give his opinion I would like to hear about it....

Beside that, do you suggest any other modification?
Thanks.

No, I got the scoot running, then pulled the engine to rebuild. While apart I milled the third port, which I know your '76 already has. The stock exhaust was crusty and I tried the "drano" method before without much luck, so I opted to get a "econo" P150 pipe from Scooter Mercato ($39). A donor 20/20 came along, so I used that. Overall, very pleased, but I don't know what just changing the carb would do.

i have one more question, if i change to the 20/20 carb do i need to do modification to the carb itself? like change the carb jets or something?
thanks.

It should come jetted fairly close to what you need, probably a hair on the rich side.

Yes, you should replace the jets. On my original 20/15 the jets were as follows: AC 160, E1 mixer, 88 main, idle 42. My 20/20 jets: AC 160, BE3 mixer, 100 main, idle 55/160. This is on an autolube engine. If yours is premix, you may want to run a 102 main. Good luck.

you mean that i should put the jets from the 15/20 in the 20/20?
thanks...

No, looks like he's saying: Same AC - 160, E1 mixer to BE3, 88 main to 100(maybe 102 w/ premix) and 42 idle to 55/160.

well, i got the carb...
know i need to know which jets i need...

as i said, yo uphold probably bolt it on and see where it lands with what is in it.

if it is new, it came jetted for either a P125 or P150, or a Bajaj or LML 150. these will all require close, but slightly richer jetting to what you'll end up using on your super.

looking at yours, it looks about 80's era, and probably is off of a P125. fundamentally, it's the same engine as your super, but it has slightly smaller displacem,net, but better ports.

let me put it this way- there's no 20/20 that will ship with leaner jets than you need for a 150 super. if you're in the 160/be3/96 neighborhood, (P125 stock) i'd throw it on and start from there.

thank you Rob.
i will try with the jets that on it, and see...
it comes of a px150.
any way, i have my original jets from the 15/20 carb and maybe i will try with them as well. that way it will be less rich.

You've probably already noticed all this, but the slide pull on the 20/20 looks mangled and may need to be swapped to use the end on the throttle cable.

The old carb draws mixing air through a hole above and to the left that is plugged on the 20/20. The 20/20 has the hole in the top of the idle jet for air mixing. So don't put your old idle jet in the new carb. It has no air hole.

The 20/20 seems to have the Spaco type long, fine threaded, hex ended idle mixture screw. It takes more turns to make idle mix changes. Some owners shorten it by cutting off at the closest to the carb hex and make a slot for a screwdriver. The long protruding screw also is more aggravating for carb removal/replacement. Fine threads make it easier to cross-thread and damage.

Hopefully, you'll luck out and the needle/seat won't leak.

At a given rpm, the engine will flow a specific amount of air. The carb's job is to add the correct amount of fuel. As long as the carb is adding the fuel correctly (same mixture), a bigger carb size does not make the engine use more fuel. It will allow it to reach a higher rpm if the engine is designed to do so.

Good luck on the rebuild and have fun.

when i remove the jets i sew that that are not the same... thanks!

well friends, i still need your help.
i couldn't stop myself from buying small set ups for my vespa.

bought a Malossi exhaust, a pollini air filter and a BGM fast fow fuel tap.

as i was saying, my engine is stock.
i have a 20/20 carb instead of the 15/20.

now, witch jets do i need?
thank you all

Well at least you know what hardware upgrade youll be using.

Rob and others have suggested the correct tuning advice for you.
It still stands. Rather than dump a whole lot of cool parts on and hope to get the performance you want. You will still need to dial in one performance part at a time. this saves a whole lot of hassle at the next step.

Best code of practice is to follow the advice and dial in your carb for your stock setup, theres already mention of the jet sizes that could work.
THEN look at upjetting 1 or 2 sizes for your venturi and then see if the ???exhaust will work with your sidecar??? (AND UPJET FURTHER FOR THAT) I think those are little rev monsters. You may have need for a touring exhaust instead, (i am not exactly sure on this but the combo doesnt seem right).

But again, upjet for the carb first before deciding how to proceed with future performance gains, you might find theyre actually not be there if your pulling a car no matter what you throw at it.

*EDIT* Sorry just realised this is a 6 month old thread

first of all, the thread is 6 month old but i just bought the set ups yesterday.
i dont intend to make it a vespa for racing and i dont drive it to hard.
i had a good deal to buy it from a freind that it didn't fit him. i payed not much and it worth maybe double then what i payed.

he told me to start with:
main jet 160-BE3-115
ldle jet 40-120

what do you guy's think of it?

about the sidecar, it make the vespa drive much slower so i do think thet it could make a big difference. Especially in a high RPM

thanks for the help.

Oh okay cool. just thought i was doing a partanen and digging around defunct threads.

Nothing wrong with scoring cheap bits.
Im sorry mate, i dont have any 150's (at all) that will be pulling load, so i cant advise on your particular setup.

Usual jetting for tune is go rich on the main and back it off from there.
The guys that are replying are in the know. If they say start with a stock 150 setup. start from there. get yourself a jet kit, theyre cheap and itll help with your choices. But at the end of the day 115 isnt going to blow your engine, worst case is a fouled a plug or 2. Getting hold of a couple of mixer and idles are a good idea too. you can always sell the ones you no longer need once your sorted.

Bang it in, back them down if 4 stroking and see what comes of it. that way you can go back up once youve put your pipe on and see if that works pulling load with the side car.

As ive not got real specifics im going to end my goodwill rant here and let others that actually work on 150's tell you (and me) if im wrong or not.

Cheers

Liran,
Thanks heaps for letting me have a blat on the SS180, & we enjoyed the day.
I hope to get hold of one of those cool stand lock brackets. It would be good to invest in a simple (cheap, & glue to heads back on when they fall off) panel beating kit (3 hammers, 4 dollys),& smack that guard back into shape& have a go at the rest of th scoot, they seem like good painters, so let them do that bit.

Definitely use th 20/20 carb, others will know jetting better than me.
Once I get home I'll see what I can dig up to help out, I'll keep an eye on this post to see what you need.

Callum i will fix the front fender...
I am trying to get the stand lock for you... Don't worry, I will get one.

The Pollini ventori kit is for the 20/20 dellorto carb so I will use it...

I am waiting to see the other picture you took here and I hope you enjoy Israel.

I think this week maybe I will finish the engine..

Hope to see you again before you leave.

Know, back to my curb... 8)