Modern Vespa

I can't get my Vespa VBB to start after being stored for the winter. I had no problem starting it last fall and I intentionally ran it out of fuel before storing it.

Just so readers won't ask the scooter has a new LML Stella PX engine in it. It has also been upgraded to 12V with CDI.

The carb is a SPACO SI-20-20 P1805

The scooter won't even cough when I attempt to kick start it. EXCEPT it will start on the first or second kick if I pour a ¼ oz of fuel directly into the carb throat. It stops in a few seconds after the fuel runs out.

It has excellent spark.

Good compression based on what it feels like when I attempt to start it.

If I open the fuel tap with the banjo disconnected fuel runs out of the banjo like a fire hose.

There is fuel in the carb bowl.

At this point I decided the problem had to be in the carb so I dissembled the carb, did a thorough cleaning and inspection of the body and jets – everything looked good. The only part I replaced was the carb fuel filter. (The old one was probably OK.)

I reinstalled the carb and it still will not start.

Fuel is not getting from the bowl into the throat.

I have attached a graphic I found. No fuel is coming out of the "nozzle" marked number 13. Nothing I came across before I rebuilt the carb mentioned anything about nozzle 13. Is there a way to check it for obstructions?

How does fuel get from the bowl down to nozzle 13?

Any other places I should check?

Thanks in advance for you suggestions

Nozzle 13 will only deliver fuel when the air flow through the throat is sufficient, which is not the case when starting or at idle with the throttle closed. Even with the slide open at start there isn't enough flow.
If it runs on fuel added down the throat I'd think it should start with the "choke" knob out.

Is your float height set correctly. If the fuel is too low in the float bowl it will not come out of the main jet. However having said that as pointed out above , engines normally start on the idle circuit , with the main jet only coming in a 30-40% of throttle openings

SI carbs don't really have an adjustable float height, so that's not it. The float might be stuck, but usually it sticks open (or the needle quits sealing) and the bike floods and pisses gas all over the floor while parked.

Are you certain that you don't have bad gas in the system? Is the gas you're pouring in the throat to get it to fire coming from the tank? (If so, never mind this question)

For next steps, I'd take another look at the main jet stack, as that's the step past the float bowl. Make sure the main jet is not blocked, in particular the hole in the tip of the stack.

You can sometimes test this by unscrewing the main jet stack a little bit (1/2 to 1 turn) and trying to start it that way. This lets fuel bypass the main jet.

Also, look down into the hole the main jet sits in and confirm there's fuel there. If there's fuel in it and the main jet is clear, then something may be jamming up the spray bar (aka "nozzle 13"), but that seems pretty unlikely, as the main jet would generally be blocked by anything big enough to block the spray bar.

You can get some carb cleaner, stick the straw down into the main jet hole, then cover it with your thumb and give it a good spray. You should see carb cleaner, gas, whatever, spray out both directions, back into the bowl (if the float is removed) as well as out the spray bar into the carb mouth.

One other outside possibility off the top of my head is that the fuel tank breather is blocked, preventing fuel from getting into the carb, but that would normally be detected when you check for flow at the banjo. This is also easy to check--loosen the fuel cap and try starting.

You've got this. Just keep at it.

So after countless kicks, did you check the plug to see if it's dry or soaked?

Assuming that plug is functional, I would guess the fuel passages in the carburettor have clogged up, especially when left to dry out.

Thanks to all of you for replying. I'm still trying to work my way through all your suggestions.

I'm priming the carb with the same fresh gas that is in the tank.

I tried unscrewing the jet stack a bit, but that didn't seem to make any difference.

I have pulled the spark plug several times. Each time it seems to be black and somewhat oily. I'm sure I'm flooding it after so many attempts to start it.

The Spaco P1805 SI20-20D was on the engine when I purchased it, and it was starting fine when I put it away for the winter.

Full disclosure: I had a difficult time getting the new engine to start when first installed, using the starting procedure in the owner's manual - choke and some throttle. Then I came across a posting on this forum that said to start the engine with choke only and no throttle until after the engine starts. I tried it and the engine started right up. That is the procedure I was using all last fall.

Here is something that has happened a few times since I received your comments while trying to start it. I'll get it to "start" with the choke only, no throttle. It will run for a couple of seconds and then seems like it is going to stall out. The instant I give it some gas with the throttle it stalls.

Does anyone know were I can purchase a set of jets for this carb? I found jet kits on line but none of them reference a Spaco carb?

The jets for a dellorto si carb should work, as the spaco carb is just a licensed copy of the dellorto. I'd try to find what changed before going down the jetting rabbit hole. When you pulled the carb to clean it did you replace the gasket underneath it? When you cleaned the carb did you use an ultrasonic cleaner, liberal amounts of carb cleaner, blow compressed air through the jets?
It sure sound like you have a clog somewhere in the fuel delivery line.
As a long shot I'd check the flywheel Woodruff key just to make sure your timing hasn't changed.
Stick with it, you'll get it figured out!

Jets are often labeled Si Dellorto/Spaco
https://www.scootermercato.com/Scooter-Parts/Jets

I don't think you should be messing with jets at this point. Nothing should have changed that would necessitate a jetting change.

How many turns out is your mixture screw? That's the one on the back of the carb. It should be about 1.5 turns out as a baseline.

Were you able to verify that you have fuel in the main stack and getting through the spray bar with carb cleaner?

Also, I assume you cleaned your idle jet when you cleaned your jets, but please confirm.

Can you share some pictures of your carb and engine (and scoot, if so inclined ), too?

It's pretty normal for the plug to be wet and oily if it's been kicked over, but is not running.

Another thing you might try is push starting it. Push it until you're at running speed, then jump on, shift into second, and pop the clutch. This will give you a more sustained and faster cycling of the motor than kicking it.

The more extreme method, and this is often a two person job, is to put the scoot in first and push it, driving the piston from the wheel instead of the other way around. On a trip this spring, we did this for about a quarter of the starts of the bike I was riding, as it had a bad float needle and would flood nearly instantly if I forgot to turn the tap off or turned it on before I restarted the bike.

I providing pictures of the carb before I disassembled it for cleaning and then back in the scooter. I have also included two photos of the spark plug.

The plug was cleaned yesterday afternoon before I tried starting it several times. It is a NGK BP5EY gapped to 0.76mm

I cleaned the carb and all the jets with carb cleaner, toothbrush, very fine wire, and an air compressor. I did all the carb work over on a clean white cloth and didn't see anything come out of it. The fuel filter was a bit gummed up so I replaced it.

As for the mixture screw I started at 1.5 turns out and then everything between 1 and 3 turns

As for pushing it. I'm well beyond the age of pushing anything to get it started.

Anyone have any thoughts on the following?

Here is something that has happened a few times since I received your comments while trying to start it. I'll get it to "start" with the choke only, no throttle. It will run for a couple of seconds and then when it seems like it is going to stall out I will try to give it some gas with the throttle. The instant I it gas it stalls.

What's your jetting?

Your spray bar doesn't look like one I've seen before, but that doesn't necessarily mean anything.

And have you checked compression? That's taking things in a little different direction, I realize.

These motors only need four things: spark, fuel air, and compression. Let's figure out what's missing, but the only thing you don't seem to have checked at this point is conpression.

I'd still pull the flywheel, to check the keyway. Strong spark at the wrong time, could give these symptoms. I'm pretty cavalier when it comes to starting fluid, so do what you're comfortable with, but a shot in the carb should kick over and run easily , and get enough air past the spray bar to encourage it . Just spit balling, but the plug is wet, so fuel is getting into the combustion chamber, carb is clean, spark is good(timing assumed to be good), all that's left is compression.

If it ran when the OP put it away:

It's not the flywheel.

It's not the woodruff key.

It didn't un-time itself.

The jetting didn't change.

It wouldn't magically lose compression.

90% of the time of the time, no start after sitting is due to (1) a fouled plug, (2) a clogged idle circuit or (3) a corroded or rodent-eaten electrical connection.

If it stalls when you give it gas, there's still some crud in the carburetor, the tap or the tank that needs to be cleaned out.

I agree with socalguy, I was just trying to rule out the other 10% of the time. Let us know when the solution presents itself, I'm curious.

I ordered 3 new spark plugs that are recommended in the Stella manual. Two arrived late today which I will try tomorrow. The 3rd should arrive tomorrow which I plan to try Thursday. If the new plugs don't work I will have another go at cleaning the carb.

I will also check the compression tomorrow.

I'd still check the keyway, while it's true that this problem can't develop when the bike is parked it can happen when you're trying to start it - in fact that's the only time I've experienced it.

It appears I ordered two more spark plugs than I needed. I put the first spark plug in, gave it two kicks and it started. I have started it 6+ times since.

The new engine was always difficult to start and now I'm thinking it was the spark plug all this time. I have been using the plug that came with the engine and had good spark when tested.

The compression was 120 psi when I checked before putting the new plug in.

I still need to fine tune the carb but that is going to have to wait until the temperature moderate a bit.

Thanks all for your feedback.

I just saw you're in Clarksville.

I'm in Nashville and have a clubmate who's also a super-solid Vespa and Lambretta mechanic who lives just over the Kentucky line from you, so we can definitely help you get it sorted if you want.

Also, we have a rally coming up (Year of the Snakes) in Nashville the weekend of September 18th if you're around.