Modern Vespa

Hi guys,
After many many hours of confusion and admittedly too much money spent on parts that haven't fixed the bike, I thought I'd join here and ask if anyone knows the solution.
I have an 01 ET2 50cc that won't start. The electric start hasn't worked for a while now, and I've tried replacing the relay with no luck so I decided to just stick to kick-start.
This worked fine for about 18 months but now my bike won't start at all. It has a new exhaust, throttle, automatic choke, and I've made sure it's full of fuel and oil. I even tried a new carb but that led me nowhere so the original one is back on. I've taken the spark plug out and tested it and it seems to be fine with a good spark, gave it a clean and popped it back in. It's also had a new fuel tap and reed valve recently which previously worked fine.
So, after all this and hours of trying to kick-start the bike, it's not running and I've no clue why. I've even sucked on the vacuum to get plenty of fuel down into the float bowl with again, no luck.
I'd rather not have to sell the bike as it would be much cheaper to keep as I only need a bike for another few months now.
Any suggestions to fix are welcome! Thanks.

I'd bet money you need a new CDI. Mine gave me hell and diagnosis eluded the shop mechanics because it was an intermittent issue for a long time (and yup, worked via kickstarter way longer than electric) - sure liked to spark when I had it pulled. New CDI and bam - cured. Since learned a lot of people had similar issues

Thanks xantufrog - I'll try replacing the CDI next week, as its the last thing I can think of other than a compression issue

Good luck! Hope that's it (easy fix).

It needs spark, fuel and compression to run. With the spark plug installed, can you easily turn it over by pushing down on the kickstarter with your hand?

It also needs a reasonably good condition battery - have you checked that and the regulator?
A dead battery can take out the regulator (and vice versa). Without those the CDI won't get the right inputs to keep it happy.

If those are good I'd recommend asking in the Not so Modern forum, as more 2-stroke experts hang out there.

It has spark and fuel, kickstarter moves freely and I can hear it turning Battery seems fine, it maintained 12v throughout me turning on lights and brakes etc and when starting it dropped to 11v but its a fairly new (about 2 yr old) battery. Not sure about the regulator, haven't thought about that but I've got a CDI on the way

If it's really easy to pump the kickstarter with your hand, it's probably compression. Normally, you would expect to re-ring them in 8-12K miles, but if it's been sitting, the rings and cylinder wall will often join forces, and make things wear out faster when you finally get it sitting again. Also, if you've had an issue with the electric choke, it might be a bit lean, and that can also melt down the top end.

A compression tester will tell you instantly if you have enough compression to run.

I've replaced the CDI and it's still not wanting to start. I've checked the spark works still after changing the HT lead and it does. It's only got 6k miles and the kickstart has always been pretty soft so I don't think I can tell if there's a loss of compression just through the kickstart, and I don't have a compression tester or know anyone that does.. Also is it even possible for it to lose compression so quick that it started fine, I rode for about 15 minutes, went to go home and it wouldn't start at all...?
At this point it's looking like I'll have to sell it for scrap and get a new bike

Selling it for scrap is dramatic. Someone can fix and use it. Doesn't have to be you, but please don't overreact and junk a special bike (et2s are arguably the first modern vespa!).

You can't check the compression with the kickstarter - the 50 turns over ridiculously easily.

Compression tester can be bought at an auto parts store for very cheap.

But here's the long and short: you need compression, spark, air, and gas. If you have them, it will start and run. I had several things fail on my et2 that prevented starting: the fuel tap, autochoke and the cdi. The autochoke and fuel tap are prone to failure due to age alone. The the choke piston sticks with age and/or sitting and tap diaphragm can leak.

If you have spark, I would check your compression, clean the carb jets, confirm your fuel tap is closed when the bike is off and opens (from the engine turnover) when you try to start. You can try a manual choke for cheap. But I'd not order new parts until you go through the diagnosis methodically since you've already replaced a bunch of stuff and swapped things in and out. Did you do the work, or is there a mechanic who has been troubleshooting with you? Compression, fuel, air, spark.

I can try to look later but I had some threads on how to do some of these things on here you could search

Here you go - info on how to check the fuel tap, clean the carb, etc:
"Won't start" diagnosis for beginners
Getting Your 2-Stroke to Run Properly

Also just to be explicit: you have checked the spark - but have you checked the spark *when it won't start*? I know you replaced the CDI so it should be fine, but just...being thorough.

Where are you located? There's a good chance a friendly scooterist can help you too

Hi. I have already put a new choke on and I tested that the cylinder in it was moving freely before fitting it and it felt fine. I've checked spark many times and it is indeed still sparking fine. Fuel tap seems to work fine (when I suck the vacuum, fuel comes out, and stops as soon as I stop). I've been doing all the work myself with the help of a Haynes manual and my dad who was a mechanic for quite a while and we're both confused as to what the problem is. I'm in Lancashire and North Yorkshire area and I'd be willing to sell the bike to anyone who can come collect it for reasonably cheap, about £150 as I'd like to recover most of the cost of the parts put on it recently.

have you tried with startgas??(ether or what you call it over there:)

Yes I've tried some Auto Extreme Engine Start spray that's meant to work with petrol and diesel engines and that also didn't help.

im with the guys above...i bet you have low compression and its not even able to pull fuel from the tank into the bowl ...if the bowl is dry then i bet this is it

if you try to start it and the bowl is full of fuel you might not have low compression...it might be a bad fuel tap...its a very common part...you can test it by disconnnecting the fuel line that comes from the tank to the carb....if fuel pisses out non stop then you need a new petcock...these are super cheap

fuel leaks for a couple seconds and stops, sucking on the vacuum pulls fuel through fine, so I'm quite certain it's not the fuel tap

Not to get grumpy - but I would note that was the point of my post above: that you should test if "opens (from the engine turnover) when you try to start"

If I understand your post correctly, you've now done that? Left the vacuum hose connected to the scoot, and simply disconnected the fuel line to the carb. Crank it over and over and it should just pour out like it does when you suck on it. But it doesn't?

I don't think we can help much more until you test the compression - signs are pointing that way

sounds like a compression test is in order....its actually very simple test once you have the gauge.

if you have low compression, the remedy is much simpler than you might think. There are a few steps but its fairly straight forward and you can probably do the entire job in a couple hours if its your first time.

Basically like was stated above, it really only needs new rings. This are about 10 usd.

You can also decide to spent a bit more money and upgrade the top end to 70cc with a 70cc big bore kit. With the exception of replacing the piston you will be taking all the parts off to do the rings anyway. A 70cc kit will give you much more performance than stock. I have done a top end on an et2 about 5 times and can help you with this install if you need a hand.