Modern Vespa

Hello,
I had a working ET4 150cc for around 1 year that I did some upgrades to:
Polini 190cc kit, Polini variator, clutch, belt, bitubo suspension etc. (I will post in the other section about the modifications).
After the upgrades it was working almost perfect. There was little sputter from time to time but nothing special.
Slowly but the scooter started to have problems with the fuel mixture (as far as I can think). When cold it was working relatively OK but after it gets warmer it started cutting off when on stable throttle. If you keep twisting ON/OFF it was working OK but on steady lets say 1/2 or 3/4 it was sputtering badly. I used to drive it around 1 month before the situation became very bad.
I had previously cleaned the carburetor 1 or 2 times prior the upgrades (I have been riding dirt bike since 2004 when I was 14) so I have done that more than 20 times already to different bikes.
Before the winter came (in Bulgaria it means November until March) it was getting even worse. Actually you cant ride it because of poor behaviour. I tried different main jets from 82, 85, 88, 92 and 97 and I couldn't get it to work OK. Also the fuel/mixture screw was adjusted many many times and it just wasn't OK. The main problem is that each day was different and it seemed that no matter what I changed nothing was working better.
As the carb is 20+ years old I noticed some issues with flakes (deterioration) on the slider, I cleaned it with fine sandpaper but it didnt change anything.
So only option was to buy new carburetor. I couldnt find new Walbro (stock) so my option was a Keihin replacement that came with other ET4 150. It was pricey and still stock. I found a very good priced Naruko 30mm (VS 24mm stock) and now I am trying to make it work. It fits OK (impossible to adjust the fuel mixture screw while installed) but anyway it is decent fit.
I have minor issue - it doesnt start and I am pretty sure that I have not connected it properly because it has extra vacuum hoses that I have no idea how to connect. I wrote emails both to manufacturer and to seller in Germany and both said to turn to repair shops. Honestly, there are none local ones that are interested in working with Vespa tuned bike with aftermarket carburetor so I have to fix it myself. I have been working so much latelty that I have barely got time for the Vespa unfortunately.
If I cant get the bike to start with that carb I will try to borrow another one from a Vespa club member to test and see if the carburetor is the only problem. As far as running - the 190cc is a beast, pulls hard and while it was working OK it was perfect but the condition of the fuel mixture was getting worse and worse.
I am attaching 2 videos about the carburetor - I will be extremely happy if you can help me with some suggestions. I would like to run that Vespa again this year (still cold for scooters so I have around 20-30 days to fix it )
Thank you in advance.
Best regards,
Nikola
Carb issue:
https://www.youtube.com/watch?v=eJmfIV844Zg
https://www.youtube.com/watch?v=2vXBkzpNz5A
Working before the condition became worse:
https://www.youtube.com/watch?v=GSZ0fCDsDPw
Carb installed:
https://www.ebay.com/itm/Vergaser-Naraku-30mm-Racing-membrangesteuert-Vespa-Modern-ET4-LX-GTS-LXV-GTV-G/173103262465?hash=item284dc22b01:g:i4UAAOSwZ11aXiz-:rk:1:pf:1&frcectupt=true

What does your sparkplug look like? First question is, is it running lean or rich, and usually the sparkplug will tell you. Too lean, figure out why it isn't getting enough gas (air leak. plugged jet or filter, fuel supply). Too rich, why (leaking needle jet, wrong jets, float level high, etc.).

I'd be tempted to squirt just a little gas into the intake while cranking it, to see if it starts. If it doesn't, you need more gas. Have a fire extinguisher handy, though.

Outside the box, check all the electrical connections on your ignition. Have seen more than a few cases of target fixation. The carb was the last change, therefore it must be the carb. Only to find that an ignition connector was knocked loose while installing the carb. Swapping the carb with a known good one is an excellent idea, to isolate the problem.

Nikola, the 30mm Naraku is too big for the regular 125 intake tubes. How did you get the much larger mouth attached to the intake manifold? The carb may be getting false air sucked in because the carb doesn't fit properly.

Also, I don't see any fuel moving in the fuel line, first two videos.

Last videos, you loosened the intake tube at the box, then used starter spray, but didn't reattach the intake tube. False air mixture!

Also remember, the 187 needs a stronger electrical hookup. The battery seems to act OK, perhaps the starter relay, a plug in part right next to the battery, should be replaced. Maybe EUR15 at the most. Make sure it 80Amp.

The 30mm carb may be jetted too low from the factory. But I feel a problem is with your installation. The vacuum tubes seem a little suspect to me, although I cannot give any advice with this vacuum tube issue.

I have the 187 kit. I needed a stronger battery, and I replaced the starter relay. All is good now.

Hello,
thanks for the replies.
That spark plug is put in the most awful place so checking that is necessary but PITA (comparing to the dirt bikes I ride and love). I will try to do that before installing the new carb.
Actually the Naruko 30mm fits quite decent. The inlet manifold (I bought new one for this carb only) fits after you put some force to it. I think that when tighten the ring it is perfect fit. The tube to air filter needs just few seconds with the heat gun and again perfect fit (I bought used one again just for the Naruko).
The throttle cable needed small adjustment to fit. Only 2 downsides - the air/fuel mixture screw is at the bottom and there is no way to adjust it when installed and 2nd one is - no idea how these vacuum lines work and why it was stated "Fits vespa et4" while you need phD in carburetors to know how to connect that
I was wondering if I should order brand new Walbro ($550) or Keihin CVK 2600 ($195). I have invested a lot in that Vespa so the price is not the most important thing BUT Keihin is something I love. From Walbo (not heard it before the Vespa) has given me only troubles so I will try the Keihin this time. ALso I read few comments here that people like that Keihin for their vespas.
I will have the option to return it in case it doesn't fit or work OK so next step will be the Walbro. Hope I won't have to do that.
I will keep you updated about the progress.
Best regards!

hi nikola...i write only left now, hand operation right hand.

i have no idea what all of these vacuum connections are supposed to mean. perhaps you could ask an older mechanic that has carb experience?

forget the walbro. no more parts available, factory support has long since ended.

the keihin cvek 26 works perfect for the 187 kit.

the stock main jet is #82, add no more than 10 percent, you will be fine. nakaru has sets of ten, from 80 to 90. a #86 would be a good start. #88 will work as well. the keihin carb has the m5 size. the nakaru jets fit. 10 jet kit costs around 12-15 euro.

i added just last week a keihin 26, with #86 jet, minor adjustments to mixture and idle...much better performance than walbro.

amazing, now the front wheel lifts for a moment at the traffic light.

top speed. with polini longer primary gear is 118 kmh, tacho.

195 euro is a fair price. the keihin performs better, my opinion.

greetings, michael

Hello,
thank you all for the replies.
It turns out that the cables that go to the ignition coil (one of them) was loose. So while driving it was bouncing On/Off and this is the cause of the sputter and bad throttle.
So I just squeezed tight the metal part and now I have amazing running scooter.
I bought brand new Keihin CVK and now the bike just rips! It is going crazy.
I am using stock jets. I will post a separate thread for all the parts installed.
BTW I sent emails to Naruko official to ask about the way to connect it. They replied that I should contact local repair shop for assistance.
I also wrote to the Naruke European dealer and he responded with the same.
So the guys that manufactured the carb have no idea of the product - which is crazy....
So I left it on the storage and stick with the Keihin.
Thank you again and very simple issue I haven't noticed could be annoying me for 3-4 months....
Best regards,
Nikola

Ask the guys at Naraku if they know how to stick their carburetor on a stock Piaggio 200 Liberty. That's the same cylinder kit as Polini sells as a big bore kit. I think 30mm is going to be way too much for that setup. You lowered the compression to about 9.5 to 1, so the stock carburetor for an ET4 150 should be jetted about right, and if you give it much more gas, it's likely to choke. Any time you get stumped when you are trying to tune it, you can usually use information about the stock Liberty 200 engine to get a baseline.

Here is a lot of information about the differences between the Leader 150 and the Leader 200.

https://de.wikipedia.org/wiki/LEADER_%28Motor%29