Modern Vespa

Good afternoon!

I have lurked around here for a while and found some great information while I worked to get my wife's '07 LX150 back on the road. This summer I got a 1969 Primavera 125 VMA2T for myself to ride so she didn't have all the fun.

As the summer went on, I struggled with it starting, found a broken choke cable, replaced it and cleaned the 19.19 carburetor, installed and had some more ease in starting but continued to have some difficulty in starting and it died while riding a time or two.

I believe I have it narrowed down to being intake / carburetor leak and have read through the forums recommending orange RTV and possibly an O-Ring to help the seal Vespa 100 Sport small frame carb-to-manifold leak
another thread showing an alternative Polini clamp on carburetor Polini CP21 on a smallie - making a choke cable
which looks similar to this one from Treatland(https://www.treatland.tv/polini-CP-21mm-carburetor-with-pull-choke-p/polini-cp-201.2102.htm),
recieved a reply to an an email to SIP which recommended a Polini 24mm (https://www.sip-scootershop.com/en/product/carburettor-polini-cp-24mm_20124020?q=Carburettor) which I think would require an alternative intake (https://www.sip-scootershop.com/en/product/intake-manifold-polini_21500061).

Currently it has a Faco Banana exhuast, but I am looking at both the Malossi Banana and new Polini exhausts to install this winter as well while I replace the wire harness and cables.
https://www.sip-scootershop.com/en/product/racing-exhaust-malossi-power-exhaust-banana_M3214430?q=exhaust
https://www.sip-scootershop.com/en/product/racing-exhaust-polini-original_20020340

Looking for some recommendations for a reliable carburetor and intake solution.
Will the Polini intake and carburetor combination provide the most reliable scoot?
Or do I just need to give it a better try with the 19.19, felt, some RTV and clamp it down?

Are you sure an air leak is causing hard starting? Does it rev high after starting? Any changes when the choke is pulled? What does the plug look like? That could give you a starting point. Are the electrics up to par like good points or good cdi? Is the idle screw set properly. From the pics it seems your intake or head maybe leaking. Did you tighten those bolts down? An air leak at carb to intake may/may not be the cause of starting problems.

Prob best to tidy everything up and then go with trying to get a good seal on the 19/19.

Good luck!

Definitely RTV anything you can on a smallframe! It's impossible to get to once the motors back in the frame.

As far as hard starting/dying it's either low compression, fuel related (lean/rich/flooded) or electrical (bad wiring, points, fouled spark plug. While the motors out, take a look at your spark plug and report back.

Did you replace the float and needle while you were in there last? What jetting is your carb at?

Wait a minute, if you have it apart and sitting there, it needs a big bore cylinder, long stroke crank and bigger carburetor.

Welcome aboard by the way.

I was leaning fuel/intake carb since when I first got it, it would start hard, but run fine once going. After pulling the carb to replace the choke cable is when it died while going. Before I pulled the carb, it would start hard (5 kicks, maybe more) and then not start at all if I went to coffee or bar and let it sit for an hour. Once pushed/trucked back home it would usually start later in the day.

Intake to head bolts are tight.

Thanks for the replies and welcome!

Hadn't thought as much about points or CDI, assuming spark is was more of working or not; and if running, figured it was working. The electrical does need some work, headlight and switches on handle bars don't work, hence tearing down for replacing that this winter. Is replacing with an electronic system and switching to 12V a good idea? Better to start there? SIP Vape 12V AC or DC system?

Here is a picture of the spark plug, replaced at the beginning of the summer with a few hours of run on it. Compression was around 140psi when I checked. Jets are 76, 60, and couldn't quite read the last one when it was open (42?). I didn't replace the float needle when I had it apart but did try to confirm that it was sealing when reassembled. Seemed to be sealing.

The big bore kit and replacing everything has certainly crossed my mind! Not sure my stocking is large enough for that this Christmas.

Personally I don't care what it is a 1967 VW Bug, 1950 Ford truck, 1979 Suzuki Gs750, lawn mower or scooter, I've never regretted converting to an electronic ignition. I set points precisely using Dwell angle and a digital Fluke meter. On my old Ford with a flathead 6, it started easily, cranked maybe one rotation and was idling. Pull choke out start give it a few seconds push in. After switching to an electronic setup, no choke, push button starts and idles. Plugs look better also, funny part it is still the same Ignition coil just replaced points with a Pertronix setup.

As for wiring, my personal preference is 12 vdc and a small battery. A small battery takes care of low voltage idling issues people complain about. Also most accessories you may want to add use 12 vdc as a source.

That spark plug looks richer then Jeff Bezos. Maybe the source of your starting problems but the next question is why? Maybe the spark plug has never been changed??? Maybe over time the mix screw on the carb backed itself out and now its running too rich???? Mix screw should be 1 to 2 turns out. Maybe your points are too close and retarding the timing?? Cleaning the points or changing them and setting it right may help. May the ignition coil is going bad??? Try to fix the richness of the plug and go from there with a new plug to see if it starts better.

In regards to upgrading heads and electrics, maybe fixing what you have now and riding will work. As more experience and needs are defined, upgrade what you see fit.

BTW, recently I've been going through starting problems on a smallie and thought I had air leak issues until I got some help that sent me in the right direction. My issues was the main jet was wayyy to high. Unrelated to your solution but the key was fixing the rich spark plug.

Good luck!

I'm not sure why that plug is that oily. Its only 2 points richer than stock. With the exhaust, it shouldnt be that black unless of course youve been riding with the choke on?

What color are the ignition wires going to the CDI? Green, white, red? One single red wire? You might already have the electronic ignition swapped. I didnt see a points inspection hole on the flywheel.

First half of the summer, I didn't ride with choke, actually I think the choke was broken most of the summer. End of the season I rode with it partially on, after reinstalling the carb, likely due to bad seal. Spark plug was new shortly after I got the scoot as I was trying to address the hard start.

With this feedback I am thinking that beginning of the summer my hard start was in part (or full) due to choke cable. End of the summer issues, still hard start and died, are likely due to bad seal when I reinstalled the carb.

I will check the mix screw, but I thought I had set it 1-2 turns out based on reading around here.

Electrical is a bit suspect all around. The previous owner installed a kill button (I think grounding out the black wire, but I forgot to take a picture of that). This is why I tore the bike down to install the wire harness this winter.

There are 3 wires going to the CDI, Red, Green and White. Does that mean that this has electronic ignition? Is pulling the flywheel the next step?
Is it worth checking timing to see if that's off? I have a timing light, but haven't used it without a battery.

There is no battery on this bike, if it has electronic ignition, would adding one help with starting as well?

Seems like best next step may be to clean everything up, install wire harness, new coil, new plug, new felt gasket, RTV, new shift and brake cables, confirm mix screw. Anything else which would be good to replace in attempt to eliminating potential issues?

Thanks for all this help. It has been interesting trying to figure out what has been done since 1969 and what to do to get it back to running like it did in 1969.

So your bike already has electronic ignition. It has the old reliable 6 volt AC Ducati style ET3 setup. As long as the 3 wires appear to be in good condition and no cracks/ exposed insulation/ soldered terminal ends, I wouldn't worry about that.

If you understand ignition timing, nows the time to check it with the strobe. If not, leave it alone as it was running before.

The uninsulated yellow wire acting as your kill wire raises my suspicion. The new harness will fix that.

No need to add a battery to that setup. It wasnt meant for one and wont help with ignition, just lighting. Get a line on a supplier of 6V bulbs and an extra 6V regulator.

I would do everything you listed below including filling the slits in the carb and collar with RTV, throwing some RTV on the gaskets at the intake and exhaust manifolds (undo a few nuts, RTV, reinstall and tighten. That should eliminate any exterior engine issues.

MJRally, Thank you for your help with this. I dug in a bit more and it appears that the entire motor is from an ET3, VMB stamping on case. I spent a few hours looking at wiring diagrams between the VNA and ET3. I think I understand what I need to adjust to make the new harness work and how to eliminate the yellow wire / kill button.

http://www.scooterhelp.com/electrics/wiring/VMA2.pdf
http://www.scooterhelp.com/electrics/wiring/VMB1T.pdf

I hope to get some time this weekend pulling the new harness through.

Did you draw that diagram? Looks like it should work.

If you haven't already, buy a regulator and extra 6V bulbs, all sizes. If you wired things up wrong, you'll pay the price and need a replacement.

Yes I drew it up after searching around and not finding an VMA to VMB swap diagram.

I do not have a regulator but did order 2 of most bulbs last week. How would the regulator get wired in?

On my smallie with ET3 electrics, I wired a regular into the yellow circuit. It solved all my bulb problems.

Thanks all for the regulator suggestion; I have a regulator coming in the mail found from SIP
https://www.sip-scootershop.com/en/product/voltage-regulator-sip_85154000

Pulled wire harness through yesterday, going to start landing and fitting it this week.
Exhaust is in, gaskets and shocks coming, looking forward to getting it together for spring.

Updated wiring diagram with regulator and diagram for wiring in regulator:

I made a mistake and didn't take a good picture / document the wires well before I unplugged and removed the wiring harness.

My question is regarding this terminal with fuse and what appears to be a capacitor. From the unclear picture I have it looks like: yellow on upper left connection, green on upper right, red lower right. Not sure if this bike was wired correctly, but looking at wiring diagrams, I don't see a fuse included in a non-battery version.

Do I include this terminal in my wiring? If so, where in the wiring diagram do I include? I have looked for wiring diagrams and builds to try to find this included. Any link of someone's build, or a place or wiring diagram? Or do I just skip that terminal all together?

Thanks!