Modern Vespa

Cold engine: catches immediately. Warm engine: no go. Thoughts?

Miles on the scoot? How many miles since the valves were adjusted?

When it's warm and it "won't turn over", what do you hear when pressing the starter? Anything? By that phrase do you mean that it doesn't start or that the engine doesn't even make any sound or ...?

When warm and not starting, can the fuel pump be heard for 2secs after key on? Lift the under seat storage and keep you head in there while you turn the key. If you don't hear it then it's the fuel pump. There was a recall for this, ask a dealer to check your vin.

Also there was also an issue with hot 300hpe engines as detailed in https://static.nhtsa.gov/odi/tsbs/2020/MC-10178216-0001.pdf

What does it take to start again? Complete cool down?

My 2021300 HPE had the above issue. Took my local Vespa dealer and Vespa HQ techs forever to figure out the problem. They finally zeroed in on the problem after about a year of back and forth to the dealer. They fixed the high pressure issue and my bike has been fine ever since. No more hot start issues in over 3 years now.

Your title: "2022 GTS 300 hpe won't turn over when engine is warm"

So the starter doesn't even make a noise?

Thank you, Vespa Team! To give more info, the bike has 5100 miles on it. In November, I bought it used from a motorcycle dealership that does not specialize or do repairs on vespas and I bought it understanding the dealer would not warranty it over 30 days. As a new rider (got my license in October), I have only taken it out for continuous rides (an hour to an hour and a half) and then brought it home. About a month ago, my husband (a Triumph rider) asked to take my bike out. He rode to Sterling and decided to fill up my gas tank. He stopped at the station, filled the tank with low ethanol fuel and then hopped back on to start the bike. The engine would sputter but not catch or fully start. He tried again after 30 minutes — no joy. He left it overnight (I was not pleased) and we both went back the next morning. Engine started immediately. Last week I decided to do my own experiment. I took "Mauricio" out for an hour spin (no trouble starting) and then when I got back home, I parked and turned off the engine. I tried to restart it and it would crank but not start. I tried again every 15 minutes. After an hour, the engine started right up again.

The precious owner kept a bit of a service log; looks like the last service was in July at 4,835 miles. I imagine he probably traded it in in the fall.

Even if SteelBytes has already pointed this out: The fuel pump must whirr quietly whenever you turn on the ignition. Can you also hear the fuel pump whirring when the ignition is switched on during unsuccessful attempts to start the engine when it is hot? If not and starts up when cold -> thermal problem with fuel pump.

Next time you ride it listen for the fuel pump when it's cold so you'll know how it sounds when hot. Also, is it possible your husband overfilled the tank when he filled up? With a Vespa, be careful you don't try to "top off" the gas.

When you first switch on, but before trying to start, do you hear the fuel pump 'whirr'? If not, the impeller in the pump could have expanded enough for it to stick. At one time a whole batch of them were under recall - but that's long gone. However, it can still happen, as posts here on MV have shown.

Update, Vespa Team: went riding yesterday and bike started immediately with cold engine, as usual. I did hear the whirring of the fuel pump when I turn the bike on, before I started the engine.This was my longest ride yet, at about an hour. Thankfully I was on neighborhood roads because at about the hour mark, when I assume the engine was hot, the throttle stopped giving gas to the bike. I could roll the throttle bar toward me, but no juice. I found a nice spot to park and turn off the bike. Tried to turn it back on and restart: no whirring. Waited an hour — bike was fine. I guess it is the fuel pump and I'll need a mechanic. Suggestions? I live in northern
Virginia.

99.9% fuel pump!

Try to find an official dealer, the VIN (or the serial number of the fuel pump) can be used to check whether this fault is covered by the recall.

Not sure about a knowledgeable mechanic in your area but if you are mechanically inclined, you can do it yourself. There are YouTube videos on how to do it and I think there may be one on Scooterwest's YouTube channel.

You don't have to buy a complete Vespa OEM fuel pump ($$$ like $200). The part that failed is the motor in the pump assembly. I have replaced the motors with one made by Kemso (~$40).

Decompression ...have your dealer check it

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i agree with GermanGTSDriver, its the fuel pump.

Wondering...wouldn't the bike stall if the fuel pump bound up? Or, does the pump bind up while getting heat-soaked when sitting?

Hmm ...

Random thought: when the bike is not running there's only about 12v which might not be enough when the pump is hot. Whereas if it's running the approx 14v can keep it running.

In the German forum, there are also some reports in connection with the fuel pump that describe the engine stalling while driving. However, it is much more common that the engine cannot be started after it has been switched off and can only be started after it has cooled down.

In this context, I would like to point out that this is a thermal problem with the fuel pump and that the temperature initially rises after the engine is switched off due to the lack of airflow.

Hi, yes the pump gets hot and binds its a rotary pump with to tight tolerances.

I replaced mine with kemso 13001 on a gts300 2022 HPE after consulting with them. Seem to have low pressure and the engine cranks but won't start. injector is working and cleaned (was working well before the switch).


Any advice?
What kemso model would you suggest?

Thanks:)

Mine didn't stall when riding, but wouldn't restart when warm. Replaced the starter ($32 Amazon) and it's worked ever since.

Good luck.

I had an issue with the start relay was corroded so I replaced that when I fitted the kemso pump well over 12months ago I have ridden over 5000km with no issues.

I used a Kemso 13001 pump. Have no issues

Thanks very much, was that on an HPE model?

Hello,

I have been using that pump as well, majority of the vespa scooters run the same pump regardless of engine size. I am using using the Genuine KEMSO 13001 Fuel Pump(Designed for both gasoline and E85/ethanol) the only thing I replaced was the pump and one terminal connector, I used all the original hardware.

I did so as well, but now the scooter won't start, and injector seem to have weak spray.

So either I broke something else during the replacement process, or I still have a faulty pump as it seems to have low fuel pressure.