GTS300 wont start - Flooding?

[Mike Holland]

Scooter started fine this morning, so I put on my gear and rode up to Pie-in-the-Sky, a motorcyclist pie and coffee hangout a little way up the windy old Pacific highway. Met up with friends there and chatted. Then I started the scooter again and rode further north up to the Hawkesbury river, turned around and came home. There was a little hesitation starting it that time.

On the way home I stopped to buy some milk. and then the scooter wouldn't start. Same problem. I walked home, just a short distance, and in a couple of hours I will go back to try again. It is not a proposition to push the scooter home, as there is a hill on the way.

So the ECU was not the answer. I now plan to go through the workshop manual checking all the inputs to the ECU - temperature gauges, oil pressure. I have tried Vespa workshops three times, and they cannot solve the problem. So I have to do it myself, or scrap the scooter.

I think I'll just sit down somewhere and cry.

[ET Oldie]

Very frustrating.

Is this the 300 that you tuned for more power a while back? Or was it only the vari and weights that were changed out?

[Mike Holland]

"Tuned" is putting it mildly. It has a Malossi cylinder and head, larger fuel injector, lambda emulator, Malossi clutch springs, 12.5 gram Dr.Pulley sliders, Bitubo in front and Malossi RS24s rear, Brembo calliper front and Frando rear, Akrapovic exhaust, air filter mod plus many cosmetic changes. Mechanic at the one shop I took it to said it was awesome to ride!

I absolutely love it, and now it seems I have no option except to scrap it. Who wants to ride a scooter that will strand you far from home waiting for road service, as has happened to me three times?

If I get a new GTS I will immediately want to do $3500 worth of mods to it.

[GTS-Peter]

And another example that the ECU itself is a vera reliable part on our scooters that doesn't cause trouble as much as many of the old school two stroke riders talk. It's always the same. If the problem can't be found, blame it on the "Blackbox" or in this case the throttlebody/ECU .

So the starting problem comes up when the engine is on temperature. So the problem got something to do with higher temperatures.

When the engine won't start, does it sound slightly different from the sound when you crank it when the engine is cold? Does it run like free or do you hear the compression blobs?

I am thinking about a compression problem. May you have a problem on the valve shafts and the valve is not closing Completely. This is a uncommon problem but on the malossi head it's not impossible.

Have you done a compression check when it won't start?

I am sure the problem is a little one. Too small to find it.

[ET Oldie]

"Tuned" is putting it mildly. It has a Malossi cylinder and head, larger fuel injector, lambda emulator, Malossi clutch springs, 12.5 gram Dr.Pulley sliders, Bitubo in front and Malossi RS24s rear, Brembo calliper front and Frando rear, Akrapovic exhaust, air filter mod plus many cosmetic changes. Mechanic at the one shop I took it to said it was awesome to ride!

I absolutely love it, and now it seems I have no option except to scrap it. Who wants to ride a scooter that will strand you far from home waiting for road service, as has happened to me three times?

If I get a new GTS I will immediately want to do $3500 worth of mods to it.

Ooh-rah!

Yes, mildly stated, sorry. Now I remember. Mike, but I can't imagine that changing out the electrics will still cause problems. My, how long have you been riding the modified version? This is insane. Software, software. Indeed, this news is saddening. What else is thermally controlled?

[Mike Holland]

And another example that the ECU itself is a vera reliable part on our scooters that doesn't cause trouble as much as many of the old school two stroke riders talk. It's always the same. If the problem can't be found, blame it on the "Blackbox" or in this case the throttlebody/ECU .

So the starting problem comes up when the engine is on temperature. So the problem got something to do with higher temperatures.

Thank you for your insights, Peter, but I had the ECU replaced 6 months ago when I had the problem of mis-firing at 80-100 kph. Five other people had the same problem and all agreed that replacing the ECU was the only solution. It worked in my case. So this very reliable component DOES cause trouble, and I am not just blaming the black box that I know nothing about.

And then this new problem began, slowly getting worse. I have removed all my modifications (except the V4 cyl/head), and looked at everything else, and so have two Vespa workshops, one of them twice. But they did blame "black boxes" that they knew nothing about. The first blamed my larger injector, which had been trouble-free for a couple of years, then the second said I was blipping the throttle when I started the engine, and this was causing flooding (bullshit), and next the first one blamed the second for fiddling with the ECU mapping (they did a TPS reset). Each got my scooter running so I could ride it home, and in each case it would not start the next morning.

The problem does sometimes come up when the engine is up to running temperature, BUT ALSO sometimes first thing in the morning when it is cold. So it is not temperature related.

OK, I have not checked the compression. I don't know how to. But when the scooter is running, the performance is as good as it has ever been. Same top speed up my test hill, same front wheel rise as I take off. Definitely no fall in performance once the engine is running.

[Berny1900]

Does the engine stop suddenly once it is running? Or just not (re-)start?

[GTS-Peter]

Ok, so if it sometimes just won't start (doesn't matter if warm or cold engine) and except of that, the engine runs fine, I assume to find the fault somewhere in the electronics.

Something wrong with the immobiliser or antenna?
Kill switch?
Ignition switch?

What about the Gas tank and it's air breathing vent? May the tube of the air vent is squeezed somewhere and won't allow the gas tank to breathe so that the fuel pump can't work correctly.

[Mike Holland]

Everything checks out perfect until I press the starter button. Even then it does everything it should except the ECU seems to make a wrong decision and pumps too much petrol through, flooding the engine. That is how it seems to me.

But a new ECU made no difference, so maybe it is one of the signals coming into the ECU that is wrong and misleading it - a pressure sensor or temperature sensor or voltage reading or such.

[Berny1900]

Pickup Signal is OK? Maybe wrong ignition timing, which means a spark comes when the piston is down.
Pickups are known to have issues.

[GTS-Peter]

Or the fuel pump with integrated and self regulated pressure adjuster is faulty.

How do you recognise that it's too much fuel injected?

[mikesch]

Die Düse kann klemmen und nicht richtig zu machen, dann hast du auch eine Überflutung.
Wurde die Düse schon getauscht?
Ob ein Ansteuerfehler vorliegt kannst du mit einem Oszilloskop feststellen.
Es sollen im Leerlauf nur kurze Nadelimpulse an der Düse anliegen.
Zur groben Einschätzung schalte eine einfache LED mit 560 Ohm Vorwiderstand parallel zur Düse.
Bei meinem Motor habe ich die blaue LED gleich eingebaut gelassen.
Seit dem weiß ich z.B. das im Schubbetrieb kein Kraftstoff eingespritzt wird.
Ebenso kann die Impulsbreitenänderung beim gasgeben exelent beobachtet werden.
Das ganze geht bei Vollgas und hoher Drehzahl in ein fast Deuerleuchten über.


The nozzle can jam and not do properly, then you have a flooding too.
Has the nozzle already been changed?
If there is a drive error, you can determine with an oscilloscope.
There should be only short needle pulses at idle at the nozzle.
For a rough estimate, switch a simple LED with 560 ohms resistor parallel to the nozzle.
With my engine, I have the blue LED installed the same.
Since then I know, for example that no fuel is injected in overrun mode.
Likewise, the pulse width change when gasing exelent be observed.
The whole goes at full throttle and high speed in a nearly continuous lights ..

[GTS-Peter]

A damaged injector would also cause trouble while the engine is running. It must be something related to the first start impulse. That's why I am thinking about the immobiliser and the antenna.

[Mike Holland]

I have changed the injector a couple of times. No difference.

When I switch the ignition on, the fuel pump primes to the correct 2.5 psi. When I press the starter the starter motor engages and the crankshaft turns over. Would these happen if the immobiliser or antenna was faulty?

I assume it is flooding because two workshops have told me it is flooding and say they can smell the petrol (coming out of the exhaust, I presume), and also because I have cleared the problem on a few occasions by removing the plug and injector and running the starter to clear out the throttle body.

[mikesch]

Die Wegfahrsperre würde bei einem Fehler den Anlasser nicht freigeben.
Dann schau dir mal mit Hilfe der beschriebenen LED an der Einspritzdüse genau an was beim Start passiert.
Die LED mit Widerstand habe ich parallel zum Kabel des Düsensteckers gelötet und isoliert.
Nicht den Stecker öffnen.

The immobilizer would not release the starter in case of an error.
Then take a look at the injector with the help of the described LED exactly what happens at the start.
I soldered and isolated the LED with resistor parallel to the cable of the nozzle connector.
Do not open the plug.