Modern Vespa

Hi, I'm new to the world of modern vespas.

I recently picked up an lx50 4t from my wife's cousin with the intention that my wife would start riding it. It had issues starting (only in warm weather).

It seemed to struggle to start and immediately idle poorly, often dying without gas. Once ridden for 10mins, it would idle well and start again easily. The kick start would work after a load of kicks.

Since last week, I replaced the battery but it didn't help. I've cleaned the carb and the idle jet 4 or 5 times now. I completely replaced the e-choke, cleaned the air filters and the spark plug, but still no joy. In fact now it refuses to start at all 😭

There is a clear spark, so I assume the CDI is good. The plug is also wet. I can't see any broken tubing either. The kick start fails to work too now, no matter how many kicks I try.

At a loss as to what to check/swap next.

Any suggestions of what to try are much appreciated.

Thanks, Alan

Hello and welcome! Congrats on the scoot!

You didn't say what year is this bike, or how many miles?

I think you said the bike had starting issues even before you came to own it?

Hard starting and poor running sounds like a dirty carb. I know you said you cleaned it. Are you sure you got every passage? Is there maybe a torn diaphragm, or something like that?

I'm not clear if you replaced the spark plug? Your post reads almost as though you cleaned it, but I'm not sure how that would work.

You said no broken tubing. Do you mean the fuel and vacuum lines are good? Did you also check the inlet manifold for any cracking?

Thanks for your helpful reply, berto.

I finally managed to get the scooter running yesterday using the kick start and with the battery disconnected. Again, once warm it ran fine and would restart (I reconnected the battery and used the e start afterwards). But once cold it was again near on impossible to start.

The bike only has about 7000km on the clock. Not sure of the year as I only officially buy the bike and get the papers today! Guessing around 2006-09!?

I sanded the tip of the plug and tested it against the engine casing. It gives a good spark, so that base is covered. Plus it runs fine when warmed up.

I haven't checked the diaphragm yet. Will do so today. I will also change the vacuum line as it may have a crack that is not visible. I'll also inspect the inlet manifold closely for any faults.

Could the fact that it runs fine once started, imply the vacuum line is the problem? The plug is wet suggesting it gets some fuel, but maybe not enough to initially get it going. I'm only familiar with gravity fed fuel lines in 60s scooters.

Another possible symptom is that the acceleration feels quite slow and until warm it struggles to hit top speed of 47kph. Not sure if this is normally on a 50cc.

Sorry for the long message!

Alan

So I found a small crack (see pic) in the vacuum tubing and replaced that. Fuel hose was fine and is clear.

Can't see any faults with the diaphragm either.

Got it started (I had managed to fire it up earlier so it was still warm) and it still doesn't idle well and will conk out without some gas. I assume it should idle evenly straight away with help from the e-choke and that is on a timer?

Tempted to try a completely new 38 idle jet from scooterwest (and a 78 main as I read that improves acceleration). This would irradiate the possibility of a blocked idle - even though I've cleaned it thoroughly.

I'll let it stand for a couple of hours and see if it starts easily with the e-start...

Well, sounds like some progress!

Another idea: What does the shop manual (it should be in wiki, if needed) say about interval for checking valves clearances? And have yours been checked? Out of tolerance valves can cause start/run issues; especially temperature dependent.

Okay, thanks.

Off the top of your head, do you know if valves easy to access and calibrate? ie is it the kind of job I can do in my garage or does it require special tools at a dealer?

Having let it sit for a few hours, the bike started just now with a bit of perseverance on the e start and playing with the throttle. Will leave it 24hrs and try it again to see how it is.

The idea of getting this bike was that it would be problem free riding for my wife, so ideally I need to get it to start and idle with issues.

Thanks for your helpful suggestions so far 👍

Hi again!

I haven't yet gotten around to checking the valve clearances, but out of curiosity I unplugged the e choke to see what reading I would get with a multimeter.

I found that when I pressed the ignition switch, it read appropriately 2.5v (from the two prongs in the open cable).

Shouldn't this be 12v?

I keep thinking how the symptoms would suggest a problem with the e choke. It runs/idles fine once warmed up and will start again no problem. From cold it is very difficult yo start and doesn't idle...

That is a little strange, as I would also expect 12V at the autochoke. But this is with the bike running. With just the ignition switch, maybe it's not yet getting full voltage so this test could be misleading? Are you able to measure voltage in the rare times you get the bike to run?

My understanding the autochoke works sort of in "reverse" - its rest state is open (extra fuel going into engine). As it heats up, the plunger extends and blocks off that extra fuel. So a malfunctioning autochoke would normally not affect starting, but would cause the bike to run poorly (rich) at temperature.

You could remove the autochoke and test it (there's usually a procedure in the workshop manual, which should have a link in the wiki): typically you start cold and note the plunger extension. Then you apply 12V and confirm that it extends ~5mm over after a few minutes.

Is it possible that the auto choke has failed in the closed state, ie fully extended?

It is very easy to access the valves. Just open the panel in front of the engine by your feet. Disconnect the spark plug boot from plug. Unclamp and remove the air tube to the top of the head and 4 bolts later you are looking right at it. Use the kick start lever to rotate engine to TDC and check and adjust the valves.

No special tools needed but the 8mm mini socket wrench with the flat head screw center is really nice to have. (Valve tappet or adjustment tool)

I see what you mean about the plunger position, but doesn't the e choke also have a heating element?

I will test the e choke to see if it extends when it has a 12v supply. I'll also try to test it with the scooter running - once I manage to start it! 😁

quote="berto"]
That is a little strange, as I would also expect 12V at the autochoke. But this is with the bike running. With just the ignition switch, maybe it's not yet getting full voltage so this test could be misleading? Are you able to measure voltage in the rare times you get the bike to run?

My understanding the autochoke works sort of in "reverse" - its rest state is open (extra fuel going into engine). As it heats up, the plunger extends and blocks off that extra fuel. So a malfunctioning autochoke would normally not affect starting, but would cause the bike to run poorly (rich) at temperature.

You could remove the autochoke and test it (there's usually a procedure in the workshop manual, which should have a link in the wiki): typically you start cold and note the plunger extension. Then you apply 12V and confirm that it extends ~5mm over after a few minutes.
[/quote]

Thanks! I'll do this too so that this base is covered. 👍

I just wanted to let you know that the problem seems to have been the valve tolerances as you suggested.

Having managed to get the scooter started, I was able to test the e choke and rule that out (the needle physically moves out).

I then opened the valve cover and found the gaps were smaller than the 0.10 and 0.15 needed. Reset them and now it starts straight away Will test it again tomorrow, but so far so good!

Many thanks for all your useful help and suggestions.

Happy riding!

Alan

Good job, and happy riding!

Good to hear!

I am about to do this work as well, but how do I find TDC? Doesn't seem my 2017 Primavera 50 has all those markings that service manual shows?

I didn't need to find TDC.

Assuming your primarvera is the same as my LX, just reset the valve clearances to 0.10 for the intake and 0.15 for the discharge.

After reseting these, my lx starts every time no problem.

Good luck!

Actually, now I think twice, I did have markings I lined up to get it to dead centre (which of course is needed - sorry, long day and my brain is on cruise control). The markings were on premade so I didn't need to do any measuring myself.