Modern Vespa

Hi guys,

I have a Liberty with a 50 4t 2v engine (so same as is in the LX from around 2010) and I have been having some weird problems with the starting.

First off, battery is new and is charging nicely, it is at aprox. 13V and while it runs with revs its at 13.8 to 14.5 V so that is not an issue.

I was thinking it might be the relay but, if I bypass it it is still the same. Wires from the battery to the relay and from the relay to the starter dont show any unusual resistance and the terminals on the starter have been cleaned.

It does kinda feel like the bendix is shot, as it helped for a few starts when I leaned the bike over, but after inspecting, the bendix looks good and with the cover off (and spark plug out - we will return to this) the bendix engages and disengages perfectly. It is also only 2 years old.

As bendix is fine I think it might be the starter itself. As mentioned before, when I take the spark plug out, and there is no compression, the starter (and bendix and everything else) engages perfectly and spins the engine fast enough to crank over, but as soon as the plug is back in the sounds are like the starter just cant get it to spin. It spins like 4-5 revolutins and than it gets stuck. After 1 to 3 second pause it spins it again for a few revolutions and stops and so on and on.

Do you think I shoul replace the starter motor itself? It is not an OEM unit anymore (RMS) so I dont think I can rebuilt it, and kinda dont want to just throw money at the problem (I hate it when people just change parts until it eventualy works again).

Other mods include Malossi variator and red filter, SAS and kickstart delete (almost burned down when it cloged the SAS, and the kick start never worked anyway). I suspect the carb might be upjeted but I dont know how much, it does run just slightly rich...

Any thoughts will be enormously apriciated!

And sorry for poor spelling

One thing that worked 100% on our LX150 that wouldn't even start well with a new starter was to install a LiFePO4 (LFP) battery instead of a lead-acid (L-A) one. This has a standard voltage of 13.2V rather than 12V, and holds its voltage even under high current (i.e. starter) conditions. Vroom-vroom! They are now the same price as good L-A batteries.

I tried with the battery booster, but it is not much better, it does eventualy turn it over enough but... And the battery is like brand new, 1 month old...

It really feels like the starter motor is not strong enough.

i wonder if the valves need to be reset? You should probably do that anyways

Head was redone 2 years ago, so it might be time for a check, hope its doable without droping the engine.

very easy to do. Remove the plate near the rider's feet that covers the sparkplug. You can then remove the valve cover.

Make sure you know what you are doing in terms of setting valves and top dead center. And how you will turn the cylinder over by hand. You said you removed the kick starter, so likely you will have to remove the variator cover to get access to the drive shaft to turn by hand

Yeah I have the know how, its the tools and space I lack ATM 🤣 and time of course...

I still think a new starter might help, as bad clearances would not really couse the lack of starting power, for lack of a better word.. 🤔

Before paying for a new starter, do voltage drop tests between -ve battery terminal and starter body and +ve terminal to starter relay and starter relay to starter itself. It might just be that one of those links is slightly high resistance and causing the low power at the starter. You'll need a friend to help unless you have good long meter leads.

So, another symptom, when its worm-ish outside it starts, albait hard, but in the mornings not at all... Again battery is brand new.

Have you tested the voltage drops as jimc suggested, and measured the battery voltage while the starter is trying to turn the engine over (under load)? "New" batteries can be bad sometimes.

I'm liking a valve adjustment.
O.s.

Ok, so tomorow I will do the valves (my dad who rebuilt it last time as I was pressed for time kinda agrees that it could be the coulprit) and check the voltage drop during starting. Will report back, thank you all, Modern Vespa is the best.

Valves done, exhaust was at 0,25 mm and intake was at 0,15/,20 mm, now both are to spec, 0,15 and 0,10 mm. Runs ever so slightly smoother.

The rockers have about 0,30 mm play between them is that OK?

The voltage at the starter is 12,5 ish (at batery 12,51 ish) so 0,01 V of difference, all in normal range I would say (but that was checked previously).

The battery voltage at cranking though is a bit worrying, normal is 12,5 ish and at cranking it starts at 12,5 than falls to 10,0 (saw 9,90 for a sec) ish and later (3 or so sec later) balances at 11,5 V.

The starter on its own does make some weird noises, which I am fairly certain (having replaced some before) is failing brushes.

I think I will replace the starter (dont have the will to source the brushes TBH), and if it wont help the battery too as it is still in warranty.

If that doesnt help it is going over a cliff

So, to close the case, and thank you all for brainstorming and nitpicking with me, much appreciated. Alas, 'twas the starter!

It stopped working completely last week, so I opened it up. The brushes were shot, and the commutator (or "pickup," as you called it) was not much better.

I ordered a new OEM starter (albeit old stock), and it now spins it up and starts on a dime.

I do have some troubles with the carburetor, but that's a story for another day.

Cheers, guys! You're amazing.

If you have questions as to whether the starter works or not, the easiest way to check that I know of is to pull it out of the scooter, hook up a 12 volt battery to it and push the output shaft into a piece of wood. If there's enough friction to make the wood smolder, it's good. If it comes to a stop without much effort, it's not.