Li150 Strange Starting Issue - Vaccuum Fuel Seal? Compression Seal?

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wrecklessrobbie
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I had similar problems, after doing all the usual checks and changes, cdi, spark plug, ht lead. Was going to look at ring gap next but
I was advised by chiselspeed to change my carb.
Got them to fit and dyno a new Polini 23mm carb.
Transformed starting the scooter.
Starts all the time between 1 or 3 kicks from cold.
3% mixture.
Not as fast as the 26mm jetex i had on it, but lots, lots better.
kurtminus
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Hey folks,

A little update. My plug looks really good after a ride. When I go to start the engine I’m careful not to flood it, so I turn the fuel On for about 10 seconds then shut it off. It more or less starts on 2nd or 3rd kick now.

It does take a minute or so to warm up where you kinda gotta baby it, throttle will bog it out. Could be choke adjustment maybe or lean choke jet.

Anyways starts much better when I don’t kick it over a million times with the fuel on.

I’ve been running with a lot of oil. Guy I bought it from recommended between 33:1 and 24:1 which I settled on 4.5oz per gallon. You’re saying I should use 3% max? That would be closer to just shy of 4oz per gallon. I’ll try it. Need to fuel up today.

On plugs and caps. I have an Ngk cap and plugs I bought from reputable local shops. I doubt they are counterfeit. Can you provide some links or search terms for preferable caps or plugs?

Thank you!
kurtminus
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bump :-)
Warkton Tornado No.1
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Apart from SH2/22 & some internals being mentioned, we have no assurance of the capability of the carburettor to supply fuel efficiently. The OEM Dell'Orto SH range functioned extremely well on the engines they were intended for & in latter years, many Lambretta owners have 'reverted' to them as a means of achieving a more 'civilised' state of tune. As a consequence, OEM Dell'Orto SH2/22 is regarded as something worth having, even if not in use. Personally, I have three "& a half" that I'm hanging on to, with no real plan to their use.

No doubt, I'm not the only hoarder! However, there are remade copies. My understanding is that they can be made to function well, so they, too, have their fans, no doubt experts in how to make them emulate the originals well. Because Forums (such as this) are a good way of information exchange, even I am aware that there can be issues with the float as well as other internals. Apparently, the OEM Dell'Orto components fit the copies, which is a good way of achieving parity.

With respect, to go forward & get this Lambretta functioning as it should, you should strip the carburettor down & check every component to ensure it all functions as it should.

That done, Innocenti dropped the petroil mix to a leaner 2% (50:1) with the revised crankshaft introduced in the 1960's. Two stroke oil has advanced since those days, so that ratio should be even more than safe now, dependent upon state of tune.

As explained previously, I no longer have the allegiance to NGK that I once had. Regardless of the fact that NGK are targets for counterfeiting,I have found their genuine plugs to be 'fussy' so my first choice is Champion. In your engine, an N4 should be recommended, but an N3 will cope with even a highly tuned engine.

I suggest you look @ AF Rayspeed's website for details of the relevant Champion products.

I hope that helps, but please let us know how it goes :D
kurtminus
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I’m noting now that I’m running less oil, 32:1 it starts much easier and seems to run smoother. I think I’ve been oil fouling the plugs a bit trying to get it started maybe. I’ll keep at it and let you know.

I run about 3oz oil to a gallon in my Vespa, like 2.3% or 42:1 or so. Mopeds ive always run around 50:1 and those are highly tuned with huge chambers.

Maybe I’ll mess with a little less oil even. Curious. Less oil makes you rich “richer” right?
Warkton Tornado No.1
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kurtminus wrote: Wed Jun 23, 2021 6:04 am Curious. Less oil makes you rich “richer” right?
The ideal air to fuel (stoiciometric) ratio is about 14.7:1, although we tend to be richer with our two strokes. Extra oil equates to less pure fuel in the mix. The consequences are a leaner mix.

Many seasoned scooterists that have rebuilt their top ends think that adding extra oil will help running in. It doesn't as it leans the mixture!

Furthermore, they then plod around, labouring the engine @ low revs. Low revs equates to low fan speed & therefore less cooling!

Then, to make things worse, they roll off the throttle whilst in gear, usually downhill. You can do that if there is a freewheel fitted, like Saab had with their two stroke cars.....

I always say that if you have no idea of how to run in a fan cooled two stroke top end, you are better off caning it. "Use all of the gears & all of the revs" means frequent gear changes & varying the engine speed up & down the scale

However, you have no need to worry about running in @ the moment.

I would still 'blueprint' that carburettor you have! Every carburettor that comes through my hands is stripped to the bones of it, notes made, then reassembled correctly. It pays off because a better understanding of the functions is gained.

BTW. Nitrile float needles. Usually, people say they are always red. That is not the case with all nitrile float needles for Dell''Orto SH's which are common to VHB's. They can also be genuine Dell'Orto black nitrile.
kurtminus
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Thanks for the info. I’ve already pulled my carb totally apart. Everything looks fine to me and functions as it should. Jetex carbs are so simple to begin with. I have no float issues and there’s no holes or jets clogged. Seems to be working fine.

I do know from tuned mopeds how to treat 2T bikes. But those have no gears! So I am curious what’s the best thing to do when going down a steep long hill (which we have lots of in San Francisco)? Is it best to leave it in gear with the throttle closed? Pull the clutch so it returns to idle while you speed down the hill? Speed down the hill with as much throttle as possible to keep the engine cool whilst trying not to die? ;-)

Thanks!
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coaster
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kurtminus wrote: Wed Jun 23, 2021 5:01 pm So I am curious what’s the best thing to do when going down a steep long hill (which we have lots of in San Francisco)? Is it best to leave it in gear with the throttle closed? Pull the clutch so it returns to idle while you speed down the hill? Speed down the hill with as much throttle as possible to keep the engine cool whilst trying not to die? ;-)
I tend to switch between a slightly backed off throttle position to fully closed on down hill stretches or decelerating from a fast run. It difficult to explain but if you back of to the point where it 4 strokes then it is rich and safe but you don't need to keep it there all the way down the hill, just keep giving it the rich mix every now and then, you'll get the hang of it 8-)
kurtminus
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Hey Folks,

Arggg, I had issues again starting it this morning. So frustrating. Yesterday it fired up 2nd kick, NO PROBLEMS at all. This morning, I kicked a bunch of times and nothing. I pulled the plug, put it back (the usual immediate fix) and it STILL would not start. Yet it has strong bright spark! I replaced the spark plug and it fired up immediately. So weird. Anyways, it's got a new plug now and we'll see how it goes...

This is such a f**ing weird problem.
Warkton Tornado No.1
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kurtminus wrote: Thu Jun 24, 2021 4:30 pm Hey Folks,

Arggg, I had issues again starting it this morning. So frustrating. Yesterday it fired up 2nd kick, NO PROBLEMS at all. This morning, I kicked a bunch of times and nothing. I pulled the plug, put it back (the usual immediate fix) and it STILL would not start. Yet it has strong bright spark! I replaced the spark plug and it fired up immediately. So weird. Anyways, it's got a new plug now and we'll see how it goes...

This is such a f**ing weird problem.
Pretty much the reason I say NGK plugs have been fickle for me. Substitution with another make has worked for me & as my road scoot has points, Champion fine wire have been a revelation with non suppressed cap & a J flywheel.
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