Fuel starvation?

[rosscla]

What are the symptoms of fuel starvation with low fuel level in the tank?

I did about 70 miles on the pig today. It was full when I started. Below half , last 10 miles or so, when I started to get issues. I'm running in a new piston so never had it much above 50 the whole way.

As I rolled off it felt like it was dying and conked out once when I pulled up at a junction. I kicked it a couple of times, nothing. Pulled the choke out starts first kick.

When I got home it will tickover but unless I snapped it open it would die as you opened the throttle.

I had similar symptoms prior to the rebuild towards the end of a longish run.

Malossi 166
Mazz crank
Si24
Mikeck
LML reed block, polini carbon reeds

Any ideas?

[Muttley McLadd]

How big is your main?
With a standard carb on, my coop will run to dry at those speeds without fuel starvation. Above 105/110ks, it'll starve and the temp goes up.
132 main in mine, but it needs bigger.

[rosscla]

I think the jetting is - 55/160 slow running and 140/ BE6 / 122 - from an old post about mixer tubes. I'll check it tomorrow.

It runs OK from 1/4 up and is fine on tickover. The issue seems to be at 1/8 - 1/4.

I did push it up well over 60 once just to give it a go and it just wanted to go and go. It was absolutely p!$$ing down on the run up and I was soaked and frozen when I got home. Weather was the same last time and it always seems to happen when the tank is low, below 1/2.

[bazman]

Sounds more like your pilot jet blocked mate.
At them low speeds the vespa fuel tap is fine , it's only when you're above half throttle and below half a tank of fuel you'll get issues with starvation. Usually it will be pinking its head off!!

[Nerdy Norm]

I had exactly the same symptoms on my LML curry-burner (PX copy). I replaced the fuel pipe (making sure it was as short as possible, and not kinked or pinched by the tank) and fitted a BGM fast-flow tap - problems are now gone.

[rosscla]

Will give it a look today report back.

I was kind of discounting the jetting though as the motor has been completely rebuilt following the drive seal going walk about and the carb has been changed from a 20 to a 24 and I had the same problem with it before.

[coaster]

I had some problems with the newly built LML engine in my son's PX recently, not quite the same as yours but it did feel like a carb/fuelling problem. Led me a merry dance but turned out to be a faulty (new) spark plug

[GLscoot]

My thoughts are the plug, fuel line too long or kinked.

I have similar problems on my set up and just putting it down to the fuel pressure in the tank at low levels and the fact my fuel feed to carb is nearly parallel. I have thought about a fuel pump, but at the moment I am just accepting the fact I have to watch my fuel levels.

I have found a dyno shop in Hillington and this year I am definitely taking it there to see what they can do & if they have done a Vespa before.

http://www.dynotechecosse.co.uk

[rosscla]

Ok jetting is as above.

This morning it will start every time with the choke on, choke in and it hunts up and then dies. Have screwed the air screw all the way in and out and that doesn't seem to help either.

I've blown though the pilot and the stack, no different. Tried a difference plug, no better.

[rosscla]

Been winding out and in the airscrew, nearly got it to tickover off the choke at 6.5 turns out.

Dies quite quickly if you put your hand over the end of the exhaust.