HELP. Piaggio 50cc doesn't start

[xiaodoupi]

Hi there, when I was doing research about the problem, I found this forum.
I have a Piaggio Fly50 4stroke scooter. After sitting for over half year, it refuses to start again. It turns, has compression.

The things I did:
Recharge the battery.
tested the fuel line. I sucked the vacuum line, gas flow out from fuel line.
Drained the bowl of carburator, since the gas inside is too old.
I pulled the spark plug, and tested spark with a spark tester. Also cleaned the spark plug with vinegar and small rotating brass brush.
I can see spark in the tube on the tester. But if I put the spark plug tip against the metal valve cover (ground it), the spark between the gap is not constant, looks weak. So I suspect it's spark issue. Am I right?

I just ordered another spark plug, will arrive this afternoon.
It's my first time dealing with such issue. Is the spark plug a quite common issue on 50cc scooter?

How about the ignition coil? Does it turn bad slowly too?

Thanks guys

[90GTVert]

If the spark is jumping a large gap in a tester consistently then I would consider replacing the plug if it won't jump that small gap regularly assuming the gap is correct (usually 0.024"-0.028" for most 50s).

I would clean the carb after having it sit so long. I'm guessing you drained the fuel in the rest of the system already, but if not drain that too and put in fresh fuel.

[niz76]

You'd be surprised how nasty the inside of a carb bowl looks after sitting for long. I've seen lots of "flakes" that end up getting in all the little orificeseceses and clog them up...

[scooterpimp]

yea. What they said. Old gas gets nasty.

[xiaodoupi]

UPDATE:
Just picked up the new spark plug from Oreilly, and tried with new one.
But still doenst not work. I can not see spark on the plug tip when I put it against metal frame.
I don't know what the good spark should looks like on spark tester. The spark in the tester is tiny and flashing.
Ignition coil?

Any idea? guys?

[xiaodoupi]

UPDATE:
I just hooked the spark tester on a car, for comparision. It seems brighter and stronger, can jump across for longer distance.
I also tried the method I found on internet: Spray some carb cleaner into the spark plug hole as booster, then try to start. Nothing changes.

Does it mean something wrong with ignition coil? It sparks, but too weak to generate arc on the plug tip?
Btw, where do you guys buy scooter part normally?

[90GTVert]

Check the output of the stator. I'm not sure what it should be for a Piaggio 4T, but usually you'll have a trigger wire that produces about 0.5VAC and a power wire that should be 50VAC or more. Both heading to the CDI. I just unplug the connectors and kick/crank the engine over to check each wire with a multimeter with the other probe on a good ground.

You need a special device to test a CDI that basically no one has.

You can check primary and secondary resistance of the ignition coil with a multimeter as well. If you can find a manual for your scoot it should tell you how and what the specs are.

Make sure the plug wire and cap are secure.

[xiaodoupi]

Jan 24, 2015 23:06:04 GMT -5 90GTVert said:

Check the output of the stator. I'm not sure what it should be for a Piaggio 4T, but usually you'll have a trigger wire that produces about 0.5VAC and a power wire that should be 50VAC or more. Both heading to the CDI. I just unplug the connectors and kick/crank the engine over to check each wire with a multimeter with the other probe on a good ground.

You need a special device to test a CDI that basically no one has.

You can check primary and secondary resistance of the ignition coil with a multimeter as well. If you can find a manual for your scoot it should tell you how and what the specs are.

Make sure the plug wire and cap are secure.

Thank you so much.
I just tested with multimeter. There are 4 pins on the connector. One pin has 3.3vac, One pin has 0.1 very low voltage, the other two are 0.
I don't know how to upload picture. I have a diagram from service manual, also the picture of CDI pack and connector.

Based on the diagram, if it's accurate, the wire linked with stator is 3.3vac, the wire linked with pickup coil is very low voltage, the other two are zero.

[xiaodoupi]

I dont know too much about electrical things. From the diagram, the pickup coil is passive receiver of the stator ele/mag field. So I guess the output voltage of stator and pickup coil should be porpotional. Am I right?
Can you figure out something from those readings?
If the stator is the cause, what's the common case should be? The voltage lowered significantly like this, or totally nothing?
Service manual also tells the right resistance value of both coils, and how to test. I will check tomorrow.

[90GTVert]

Pic posting info :
49ccscoot.proboards.com/post/7984

Those are very low, at least from what I'm used to with my scoots. Is it cranking over quickly? If the engine isn't turning over kinda fast when you check the output will be low.

[xiaodoupi]

Jan 25, 2015 8:14:31 GMT -5 90GTVert said:

Pic posting info :
49ccscoot.proboards.com/post/7984

Those are very low, at least from what I'm used to with my scoots. Is it cranking over quickly? If the engine isn't turning over kinda fast when you check the output will be low.

Morning,

With different grounding, I got different readings. If ground to crank case, they are 575ohm and 435ohm (pretty stable between several times tesing). Ground to negative pole of battery, they are 143-144ohm and 3-4ohm. That is not too far to specification, 170ohm and 1ohm.

I will check the cranking voltage reading with ground to negative pole after battery charged. The battery is flat after long testing.

[xiaodoupi]

I took the flywheel cover off. Now I am stuck on how to pull the flywheel off. I have removed the big 15mm nut with impactwrench, but without special flywheel puller.
So far, the connector of stator is accessible. I tested, the stator resistance reading is ~1.4ohm (specification is ~1ohm), considering the internal resistance of multimeter, it's not too far. The pickup coil is over 140ohm, lower than 170ohm that specificed, I think it's not the culprit.
When crank it, stator wire output voltage is less than 7vac. I tested on both CDI connector and stator connector, so we can rule out voltage regulator does nothing on it. Compared to the value you told me, it's too low.
I didn't see the stator output voltage value from service manual. It only tells the resistance value.
Is it possible that 7vac is the expected voltage, and the problem is the CDI unit? Just curious, I don't know too much about motorcycle electric before, have learnt a lot during these days.

The diagram: 
www.49ccscoot.com/manuals/Piaggio_Tech_Manual.pdf
PAGE 137

It says '25 - 35 v ac @ 2000 rpm' at the bottom. Is it normal that 6.8-7vac @ crank speed?
If so, the problem could be CDI unit.

[niz76]

Seems like you're being very thorough checking the electrical system and that's great, but have you checked the compression? Often overlooked but it's like kicking a dead horse trying to start a scoot with low compression..

[xiaodoupi]

Jan 26, 2015 1:02:42 GMT -5 niz76 said:

Seems like you're being very thorough checking the electrical system and that's great, but have you checked the compression? Often overlooked but it's like kicking a dead horse trying to start a scoot with low compression..

I can feel pressure resistance when I kick crank it, can feel the pulse from muffler too.
But no spark, I ground the spark plug then crank it with battery, no spark on the tip.
Initially, I can see flash on inline spark tester. So I was misleaded, ignored spark issue at first.
That probably means the spark plug got some voltage, but not high enough to create arc on the tip.

[stepthrutuner]

After a scoot sets upfor a while electric connections can become laden with resistence for various reasons. Sometimes merely disconnecting and reconnecting the connectors can restore sufficient current flow for proper operation. I have personally encountered this.