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1966 Vespa 150 Super engine cuts out after 5 to 10mins

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Stewadan Avatar
Stewadan Dan Stewart
Brisbane, QLD, Australia   AUS
Hi,

I've got a 1966 Vespa 150 Super which was restored back in 2003.

It's my weekend ride and hasn't had a lot of regular running thanks to family life commitments. It started to develop this issue of running rough after about 5-10mins (spluttering) then eventually cutting out. As the bike become spluttery I was give it a little more throttle & revs which could buy you a few more minutes but eventually it would simply stop. Once stopped, it takes about 20mins before it will restart again.

I took it to a local Vespa guru last year (Pete Chmielewski at Silver Star in Wynnum QLD) to get it cleaned up & running sweetly again. Pete suspected the fuel was off and cleaned the tank / fuel system. He also fitted a new carburettor.

Despite this it keeps reoccurring.

I have also tried cleaning the fuel tank cap to ensure it is not creating a vacuum. I even tried running the bike with the cap open and it still cuts-out.

Non-vespa mechanically minded friends think it's an electrical issue however if I pull the plug out and earth it, it sparks beautifully (plug end looks perfect). It simply will not start for about 20mins (cooling down?).

To me it feels like it’s suddenly being starved of fuel.

Any ideas or guidance would be appreciated.

Thanks,
Dan

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itsraininginPDX Avatar
itsraininginPDX Matthew Hamm
Portland, OR, USA   USA
Hi Dan. I've had this happen on a p125. Not sure it's the same deal, but it was the spark plug for me. It would have good spark, but something would happen when it got warmed up. I swapped the plug and it was fine. It can really only be one of a few things though, fuel, air, or spark. If you hadn't changed out the carb, I'd say it was one of the jets. The holes in those are so small, it doesn't take much to clog them. Let me know if you track down the problem.

OlympiaScooterCompany Avatar
OlympiaScooterCompany Matthew Gatlin
Olympia, WA, USA   USA
When was the last time the motor was dropped and the seals were replaced?

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Stewadan Avatar
Stewadan Dan Stewart
Brisbane, QLD, Australia   AUS
2003 the bike was fully restored. It was stored between 2004-2008 (on blocks, fuel drained, motor wrapped etc).

Since 2009 it's had very in frequent riding (less than 500km per year).

Snozzelad-ss180 Craig E
St Austell, Cornwall, UK   GBR
Have you tried replacing the coil.? I had the same problem years ago and put a classic Vespa coil on and that solved it..

itsraininginPDX Avatar
itsraininginPDX Matthew Hamm
Portland, OR, USA   USA
Oh. That does seem the most logical next step.

caki Joe Caran
Sydney, NSW, Australia   AUS
Hi Dan, It sounds that you have an electrical problem.
Thing that can give you this kind of problems like: Points, Condenser, Coil or Spark Plug.
The reason I say that is because the engine stops after 10 minutes with some warning of splattering. To me this is a sign of an electrical component braking down as it worms up and it gets hot enough to completely fail.
When this electrical component or components cool down the component recovers its function and you can start your Vespa again.

Do this to confirm that you have an electrical fault not the fuel fault:
* Remove the engine cover and the air filter
* Have the can of "Start you Bastard". (this is an aerosol spray can with fuel in it)
* Run the engine and wait for the start of splattering
* spray the aerosol directly in the carby as the engine is running
* if the engine regains the normal idling speed or it starts increasing in revs it means you have the fuel starvation problem
* If the engine stops while you're spraying the aerosol, you have the electrical problem

Please let us know of the results so we can guide you further.

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Stewadan Avatar
Stewadan Dan Stewart
Brisbane, QLD, Australia   AUS
I took my vespa out for a 5mn run until I though I could start to feel the sign of roughness. I pulled into my garage, left the bike running and pulled off the carb cover & airfilter. I then pulled the throttle slightly to simulate average running throttle and waited.

After a few mins it started to run rough and each time I would spray a squirt of ‘start ya bastard’ down the main air intake.

There was a momentary drop in revs then it would recover and seem to run like the throttle had been increased.

I kept doing this for roughly 10mins. If I gave it too much spray at once the bike would nearly shut down.

It then stopped after another rough running patch no matter how hard I tried to keep it going with the spray.

I tried to restart it straight away with no luck even with a little spray or two.

I kept trying to restart every few mins then after around 10mins is started up again.

I repeated the process and again managed to kept it running for about 10-15mins before it conked out again.

The spray seems to make some difference it keeping it going a little longer than not.

It was a cooler day today in Brisbane (low 20s) so maybe this helped keep it running a little longer than usual?

Stewadan Avatar
Stewadan Dan Stewart
Brisbane, QLD, Australia   AUS
I tried a third time however my can of start ya bastard stopped working too! (It’s been in the shed for 5yrs)

It does make a slight difference in helping pro-long the running but eventually the motor suddenly stops no matter how much spray I try to give it.

You then cannot start it again for at least 5-10mins

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OlympiaScooterCompany Avatar
OlympiaScooterCompany Matthew Gatlin
Olympia, WA, USA   USA
If it has been since 2003, then it is probably time to replace the seals again especially if it has been sitting for some time. But Points, Condenser, Coil or Spark Plug could also be the culprit so I would start there first.

caki Joe Caran
Sydney, NSW, Australia   AUS
Hi Dan,

You done well to eliminate the fuel problem.
You are having an electrical problem on your Vespa.
There are only 3 components that can cause this problem; Points, Condenser or Coil.
First check the points. You must check the condition of the contacts, opening gap of the points as well as the ignition timing.
If the contacts are oily, burned or pitted, replace the points and re set the gap.
If the points gap is incorrect, reset the gap.
If the points are burned uneven such as one side is eroded more than the other side, replace the condenser and points and reset the gap.
If the timing is incorrectly set you will have lack of power or difficult to start, reset the ignition timing.

If all the above is working fine, you have the intermittent problem with coil. It is very possible that the coil is failing as it gets hotter while the engine is running.
Do this simple test to verify failing coil:
1. Start the engine when cold
2. Keep the engine idling
3. Before engines gets to normal engine temperature or with in first 4 to 5 minutes, use a hair drier on hot air setting.
4. Blow hot air with a hair drier on the coil. Caution!!!!!!! do not over do it. Keep a distance from the coil otherwise you will melt the coil wit to much hot air.
5. Blow dry the coil same as you would blow dry your hair. The aim is to over heat the coil during operation. If the coil is failing internally, engine will stop.
This test simulates the coil brake down without having to take the scooter on the road test.
If engine stops, replace the coil.
Pleas be careful, do not over expose the coil to hot air. Periodically touch the coil with the back of your hand to test the heat. You shouldn't burn your hand on the hot coil.


Please let me know of your findings.

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