Modern Vespa

Hi all, long time no speak. I'm hoping you won't hold that against me though, as I could really do with some advice.

I have a 2016 registered 70th Anniversary GTS300.

Had issues with random cutouts a couple of years ago which turned out to be the battery (the scooter had been standing for some time before I bought it.

Since then I have had the occasional stall, but I also had those on both of my previous GTS.

However in the last two weeks it's become progressively worse. The scooter starts fine, but idling speed seems too low and there's a bit of a knock. Also while under power the scooter pulls like a train, when I roll off the throttle it will stall. Sometimes it starts again on the first go, sometimes the 6th.


I did wonder if it was the battery again as I had a non-scooter related accident last summer and couldn't ride again until late last year just as the weather turned bad. I replaced the battery. It ain't that.

Today a mate came round and spent all day doing the necessary to drop the engine and check the valves.


It ain't the valves.


We put a multimeter on the battery and it seemed to be behaving as expected.

I'm wondering if it's a fuel issue, but I don't think the symptoms are typical of a fuel pump failure… Or are they?

Would welcome some hive mind input into possible issues and solutions

Fuel system not venting properly?

Good luck.

You might want to tell how many miles on the bike, when you do this type of post. Check your spark plug cap.

If the check engine light comes on is propably a faulty ecu

Between 9 & 10 thousand miles. Cap and lead changed 2 years ago and looked good today when the engine was dropped. Plug was in good shape..


No ECU light, but the fuel light doesn't show when the pre-ignition sequence starts although the pump can be heard priming.

Installing an NGK Iridium sparkplug strengthened my idle at stoplights.
O.zs.

Check the air filter and exhaust gasket. Pull the injector and check the spray pattern.

Filters and gasket are good. Injector check is one of the next things. What should I be looking for?

I have no idea on that one. Check some utube vids, or swap in a good one if you have one available. I'd definitely be checking for air leaks on intake manifold and at airbox pipe.

No 🤦‍♂️

Clean the throttle body, especially the idle bypass.
https://cheekythoma3.wixsite.com/itsme/idle

Maybe the valves?

they said they checked them

Thanks to all who've replied.
I decided that before I do something expensive I should do something cheap, so I siphoned out the fuel tank and added fresh fuel (shell V-power)

This appears to have done the trick.

The scooter was laid up from August to November last year and then ridden infrequently until the UK weather started to improve.

I did run the tank quite low a couple of weeks back and it was after filling up that the issues started and got progressively worse.

I'm wondering if the fuel that was in the tank last year had gone off and that when I ran the tank low the assorted drek that can accumulate ended up in the system

Also wondering if I may have just got bad fuel?

Wouldn't be the first time. I had major issues a couple of years ago immediately after filling up.

Anyway, I took the scooter for a spin and despite trying extremely hard it wouldn't stall. 😂 hopefully I'm out of the woods with this

Well done. Fingers crossed!

Just as an update. Scooter is running fine now. I've only been using e5 fuel (super unleaded) since I drained the tank and have had zero issues with stalling at junctions or poor tickover.

I'm looking at trading in for a HPE now and will probably only use higher octane fuel in that. Lesson learned: if it's your pride and joy then it's worth the extra pennies at the pump

95 RON is fine. There should be no need for any fuel with a higher octane rating, no point in that at all.