Li150 starting troubles - fuel related?

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kurtminus
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Joined: Sat May 08, 2021 4:51 pm
Main scooter: Lambretta Li150
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Mon Oct 18, 2021 1:18 am

Hello,

I’ve got a 65’ Li150 S3 with a Jetex sh2/22. Runs fantastic, super strong spark, etc. problem is sometimes it’s really hard to start, and the only thing you can do is push it down a hill and pop the clutch. 

There is fuel in the bowl when this happens but it seems (to me) like a lot of fuel. Like the fuel is up to the top of the bowl. Also the spark plug is wet. 

It seems like maybe it’s flooding? Thing is, there is no float adjustment on this carb. Could it be something else?

Is there something tuning wise that perhaps is very sensitive on these bikes? Spark plug gap maybe? Idle jet size? Timing? Like I said it runs great once it’s started up. 

I’m pretty stumped on this at this point. 

Daggs
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Location: Addington Kent
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Mon Oct 18, 2021 9:40 am

Choke operating correctly?
What size pilot jet?
If you think the float bowl is overfilling. You may need a replacement needle valve (Red-tip) Check to see if it shuts off by holding the float up with the fuel turned on.

kurtminus
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Posts: 28
Joined: Sat May 08, 2021 4:51 pm
Main scooter: Lambretta Li150
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Mon Oct 18, 2021 4:06 pm

Daggs wrote:
Mon Oct 18, 2021 9:40 am
Choke operating correctly?
What size pilot jet?
If you think the float bowl is overfilling. You may need a replacement needle valve (Red-tip) Check to see if it shuts off by holding the float up with the fuel turned on.
Daggs wrote:
Mon Oct 18, 2021 9:40 am
Choke operating correctly?
What size pilot jet?
If you think the float bowl is overfilling. You may need a replacement needle valve (Red-tip) Check to see if it shuts off by holding the float up with the fuel turned on.
Choke operates correctly, when it does start the choke keeps it running till it’s warm enough to run without. Do you need to fine tune the choke adjustment for cold starting? Could there be too much or not enough choke? This isn’t something I’ve run into on other bikes but are lambrettas sensitive to this?

Pilot jet is 50.

Float needle tip is very clean and looks good. I’ve tested it with the bowl off just holding the needle closed with the gas on… but I haven’t tried it lately so perhaps I’ll give another try.

I’ve not been able to find a replacement JETEX float needle for this carb online, only dellorto, which do not fit.

Lambretta67
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Main scooter: Lambretta L.I. 200 special
Location: Newbury
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Mon Oct 18, 2021 5:02 pm

Try turning the petrol off before you stop the scooter. let it run a while with the petrol off. Next time you start it don't turn the petrol on till it fires up

Daggs
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Joined: Wed Jan 07, 2009 1:23 pm
Location: Addington Kent
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Mon Oct 18, 2021 8:52 pm

It sounds like the choke is operating correctly. A 50 Pilot jet is quite big. I would put a 45 in it and see how that works, also reset the mixture screw.

http://www.scooterrestorations.com/lamb ... dle-jetex/

They also have 45 and 48 pilot jets.

http://www.scooterrestorations.com/lamb ... -45-jetex/

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