Modern Vespa

Hi All,
Would love some wisdom from the forum.

I have a GTS300 HPE 2022 ABS.

I had the dreaded fuel pump issue and replaced the original with a kemso 13001.

Important to say, pump was working when cold (hot start was the issue) and the vespa was functioning well without any issue.

It required some fiddling, drop the engine, fuel tank etc... and pump went in ok.

When trying to start the engine, it cranks but won't start.

I'd love to hear your thoughts of what to check.

What I've tried so far:
1. Checking fuses + relay + pump is priming ok
2. Disconnecting fuel line, fuel is coming out when pump is making priming noise
3. Spark plug has a spark (checked via the cable to the body, did not take out the spark plug)


Any ideas would be appreciated

Try the other key.

it wouldn't crank if it was an immo problem. he said it cranks.

is the cranking slow or normal speed? ie, could it be the battery a bit too low?

does it sound like it's spluttering and trying to work?

Thanks for the battery advice, I'll check the battery today, although a little strange that battery would be weak after just a few hours.

It cranks normal like it's trying to start but nothing is happening😔.

The only reason i mentioned the battery was incase you hadn't ridden for several months while you were getting the new pump.

Easy to check it but i don't actually expect it to be the problem.

Can you maybe post a video of the sound of it while cranking?

In tugging around on the fuel line while removing/installing thee pump, you may have damaged the injector fitting - they are somewhat fragile, especially the electrical connector.

Thanks, I'll try and record and share.

Thanks I'll have a look at that as well and report back.

Update. Checked the spark plug seems to have a good spark.

Checked the injector as well, it seems to spray very little compared what I see online videos, might need a clean (although it didn't have any issue before the fuel pump change)

Next steps:
1. Clean injector
2. Check if the kemso 13001 pump isn't sending enough pressure, replace it to an oem pump.

So you said you have check fuel flow here and there was flow.

- Remove the injector out of the inlet manifold and see if there is a spray pattern or any fuel coming out of the injector.
- You should be able to feel the injector pulsing when you crank it over.
- you will need to make sure the fuel and electrical are connected to the injector.
- If its blocked, remove the injector basket filter and clean it with brake clean.
- if it doesnt pulse its the injector or power plug to the injector.

If yoou only replaced the pump and it wont start you have missed some thing.

Thanks for the explanation. Injector has very weak spray pattern. I'll clean it and see if results improve. I'll also check if it Pulse.

Before the fuel pump switch I didn't have any issue with the injector, so I'm not a 100% that the replacement pump is working well or that is provides enough pressure.

Removed injector, cleaned it, seems to work just fine. So back at square 1.

It just might be that the kemso 13001 isn't a fit for the new hpe vespa.

I'll order an oem pump and report if this solves the issue.

Thanks for the advice so far everyone 😊

I'm using the same pump in my Vespa HPE.

After getting a fuel pressure gage, it seems the kemso 13001 is faulty and can't generate enough pressure.

I'll be replacing it with an oem pump.

I'll update the thread once the issue is resolved.

Interesting. First I heard of a faulty Kemso pump

So, finally oem pump has been Installed (price is very expensive 😅) and scooter went back to working as usual.

So it seems either I had a broken kemso pump, or that the 13001 isn't a match for the HPE models.

I hope this will be beneficial for someone 😊

Is Kemso reliable? I've only found it and quantum for rebuilding pump assembly.

It appears my Vespa is acting up. It's showing signs like when the Xmax pump went out.

Also have a pump assembly for an Xmax that fits the same 13001 pump. Went down all kinds of rabbit holes before ordering a replacement OEM pump assembly. Been thinking of rebuilding it to keep on the shelf. Obviously the current pump in the Xmax won't fail when I have a spare on the shelf ready to go.