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"Won't start" diagnosis for beginners
There seems to be no shortage of "my scooter won't start" posts here on Modern Vespa. I think there is no way to write a cover-all guide on this, because there are a lot of funky things which can go wrong, so every "won't start" instance has the potential to be different.

But there are a few logical starting points which apply to most modern vespa models. If your scooter won't start, there are some things you can check without forking out the big bucks to a mechanic. Not comfortable with wrenching? It's ok! The steps I walk through below are within almost anyone's capabilities and you'll feel better having tried these first, even if it ultimately winds up in a shop anyway.

**Besides my introduction to basic diagnosis here, see this set of links in the WIKI: Troubleshooting**

I'll also request that Fuel-injected gurus post some tips below... I don't know my way around such machines

SO, if you have a Piaggio-manufactured scooter of the modern era (thinking CVT scoots of late 90's onward), particularly a carbureted model, here are things you can start with:

1) are you holding a brake lever on when trying to start? If you are not, you should. The brake switch is tied to the starter circuit. If the engine simply clicks and doesn't turn over, despite your holding the brake lever down, try the other brake lever instead! The switch may be finicky, disconnected, or broken on the lever you were first trying to use.

2) is the kill switch set to on? Even if it is, flip it on and off 5 times or so, then try again. Switches get corroded. By using them, you scrub some of the corrosion away and might re-establish a connection which had been disrupted.

3) is your battery charged? You should read at or OVER 12V on a 12V battery. If it says 10V, it's toast. Doesn't matter that 10V is "not much less than 12V" - you can try charging it from this point, but almost surely you will need a new battery.

4) is your fuse (or fuses) ok? Different scoots might have them in different places. I don't know. On the ET2, there is one under the battery cover next to the battery. To check: within the clear body of the fuse you can see the metal - looks kind of like the guts of an incandescent lightbulb. There should be a bridge of thin metal in the middle between the two prongs. If this bridge is broken or burnt looking, just like the filament burning out on a lightbulb, in means getting a new fuse. The things can be bought for next to nothing, so that's good news.

Ok, now for the meat of the issue. If you are almost sure your scoot is all hooked up and ready to start based on the above, and still flumoxed because it won't, we need to consider the following: a scooter will not run without 3 things - fuel, air, and a spark. Ok, so the problem probably lies in one or more of those categories. Let's be calm and logical here and check some basic things.

5) Checking for spark
Under the pet carrier, at the front of your engine, there is at least one spark plug. It will be hidden at first, covered by a "spark plug cap" which has an "HT Wire" (just a thick wire, usually black) running off of it.

We want to remove the spark plug. This requires pulling the cap off the plug. It kind of clips on to the end of the plug - just pull it off (can take some effort sometimes before *pop* it comes off).

With the cap off, take your handy spark plug wrench (scooters usually come with one in their tool baggy, but you can get such tools at hardware or auto stores if yours is lost) and unscrew the spark plug. *UNSCREW COUNTER CLOCKWISE*. When the plug is unscrewed, lift it out of the engine.

First thing's first - look at the end of it (the part which was in the engine). Check the color of the ceramic - shining a flashlight down into the groove to look at the base of the ceramic in particular. It should be a coffee-and-cream color on a 2-stroke, and closer to a light tan on a 4-stroke. If it is dark, and/or oily, and/or sooty, your scooter is running too rich and possibly has oil issues (too much in the mix on a 2T, or any oil at all on a 4T is bad). If it is white white, and/or flaky, you're too lean which is dangerous. If you are totally not a mechanical person, let a mechanic know about this and show them the plug. If you are a mechanical person, get a Haynes manual or something and have a blast troubleshooting.

But... back to testing the spark. EVERYONE can do this.
So the plug is out of the scooter - plug the cap back onto the plug while the plug is removed from the engine. Now, put on some gloves if possible. Hold the spark plug by the cap so that the metal threaded part of the spark plug is firmly against exposed metal (frame or the head of the cylinder are good spots). Now turn over, or have someone else turn over, your engine (as if you were trying to start the scooter). Watch the gap at the tip of the spark plug. You should see a spark, preferably blueish-white, as the scooter turns over. If you do not, make sure you're doing this correctly and try again.

If you still do not see a spark, a couple of things could be wrong. The spark plug cap could be bad, the spark plug wire could be bad, the CDI could be bad. I would start by unscrewing the cap from the wire and the wire from the CDI. Inspect the cap and the wire - the wire has a copper core which literally gets a screw tightened into it on each end (one from the cap, one from the CDI). The copper wiring can get pretty corroded with age, and chewed up from the screw. So: does anything look iffy with the cap? Does the wire look ok? If the wire looks corroded or chewed up on either end, clip 1/4" of it off. This will cut the wire down to fresher unmolested copper and might fix iffy connections. Then screw it back together and try again. The CDI is hard to diagnose - if it doesn't work, you simply need to replace it (~$100 unfortunately). You might try seeing if power is getting TO the CDI before concluding the CDI is bad (assuming the cap wiring and fuse all check out).

All of this "no spark" testing assumes you have a good battery (unless you are kickstarting, then the battery doesn't matter), you have good fuses, the killswitch is on, a brake lever is depressed, your immobilizer, if you have one, is a happy camper (see info here: Immobilizer LED codes) ... don't go buying a new CDI if you forgot to turn the key to the "on" position

And, indeed, if you are not a mechanical person, I say you've done a great job trying these things out at this point. All you needed was a spark plug wrench and a screwdriver, and you collected valuable information. If it comes down to thinking you need something pricey like a new CDI... probably have a mechanic double check if you're a rookie. At least you have some idea of where your scoot is failing.

*note* when putting the spark plug back in the engine, turn clockwise. Do NOT overtighten. Your cylinder head is aluminum, and you will strip the threads out by overtightening the spark plug. Don't be scared by this - simply screw the plug in with your bare hands (obviously you have to pull the cap back off of the spark plug before reinstalling). Once it is "tight" by hand, do maybe 1/4 turn clockwise to gently cinch it up with the spark plug wrench. No more.

6) Checking for fuel

First, let's check that gas is getting to the carburetor correctly.
We do this by checking the fuel tap. The fuel tap is located at the right of the scooter under the gas tank. It has two hoses coming out of the bottom. One is a small hose on the very bottom. This is the vacuum hose. The vacuum hose opens the tap and allows gas to flow to the carburetor when the scooter is running. The other hose is just above the vacuum hose. This is a fuel hose. This hose carries fuel from the tap to the carburetor. Before doing any tests, make sure both the vacuum hose and fuel hoses are crack free. If they have cracks (which does happen with use and age) then stuff won't work right. You need to replace these hoses, and can do so yourself with nothing more than a screwdriver to loosen their clamps. Take the hoses to an auto store and have them cut replacements of the correct inner diameter and length.

Now, to check the fuel tap, which starts and stops flow of gas from the tank to the engine:
a) pull the fuel hose off the fuel tap while the scooter is off and see if no gas runs out of the hole in the tap. If nothing comes out, that is good. If gas comes out, you need a new fuel tap - could be flooding your carburetor and making it hard to start.

b) if nothing comes out of the tap while the scooter is off (a good thing), you should now make sure the tap is OPENING correctly when the scooter is "running". Leaving the fuel line off of the tap, crank the engine over as if you were trying to start the machine. Now gas SHOULD come out of the hole where the fuel line connects. If it doesn't, your vacuum hose could be cracked, failing to open the fuel tap (so your engine is getting no gas). If no gas comes out when you turn the engine over, check the vacuum hose and replace if necessary as described above. If the vacuum hose is ok, you probably need a new fuel tap. Could have a ruptured diaphragm or something inside preventing it from opening.

Enough of the fuel tap. If it is all working correctly and you know gas is getting down the carburetor, you can check the carburetor is clean. This takes a little more mechanical confidence, but is actually, in truth quite easy. See these threads to learn about the insides of your carb (2-stroke and 4-stroke carbs are different!).
Getting Your 2-Stroke to Run Properly
2-Stroke Carburetor Set-up Technique
How a Carb Works

In particular, you want to clean all of the jets. If these get clogged, your scooter will not run well, if at all.

For fuel injected engines: the injectors, like carburetor jets, can and do need cleaning. I'll ask FI model experts to chime in with their own tips on how to work with injectors.


7) to check for air
The biggest thing here is your air filter. If it is soaked from oil, or gasoline overflow, a mouse has made a nest in there, or just so darn dirty from use... your scooter will drown in its fuel without enough air.
Check and clean the air filter. It's easy, you don't need a mechanic to do it
Air Filter Cleaning

A couple of notes to help you wrap your heads around your starting issues:
1) if you are turning the engine over and over and over and it is not starting (say you've tried 30 revolutions of the engine), and you pull the plug, it should be kind of damp looking from unburnt fuel. If it isn't, and/or you smell no gas in the cylinder, you are probably looking for a fuel delivery issue. Sure, you might not have a spark EITHER, but you've probably got a fuel delivery problem to deal with.
2) deal with one thing at a time. Don't try to fix a ton of "maybe the problems" at once. It will probably lead to more effort and money spent than necessary


I know this post is very long, and long posts make things look daunting. But the things I suggested require almost nothing more than a screwdriver. They may well not lead to the solution, but ANYONE can check for spark, check the fuel tap, and clean the air filter. And it doesn't take much more confidence to clean a carb or injectors. Follow the order written above if you are daunted by this but want to try... it's a logical progression. By jumping around to different components you'll give yourself headaches and get lost. And when done checking one thing, put it back together before taking another thing apart! You can't test multiple variables at once... you won't be able to pin down the cause.

Good luck novice trouble-shooters
Last Updated Thu Sep 01, 2011 7:30 am
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