New 185cc engine won't start or run

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johnny650
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Sun Jul 22, 2018 2:36 pm

ello ..ello...ello wots all dis ere then...?

I would have staked my life on the carb being scrupulously clean ...

I cleaned it thoroughly with carb cleaner and used compressed air to blow all the parts and jets through. its one of 4x Jetex carbs that I have been swopping around with different slides and jets all week long and they are all checked and cleaned every time they were rejetted.

So where has this come from ?? ........it doesn't appear to have come through the inlet filter which is clean. .... Its weird stuff ...almost like burnt paper in that it can block tiny passageways in jets but as soon as you touch it with your finger it vanishes into nothing :shock: :? ???

Whatever it is it must be extremely fine because I have been using a fine inline fuel filter as well as the integral filter.

Anyway its starts and runs ...allbeit rather roughly ........and with some smoke . cought cough .

I think I will take it for a run and see if it is useable as-is . There is clearly a leaky drive side seal and also a leak around the stud at the cylinder base .
I only do about 200 miles a year and so it might last the Summer out without a complete strip down.
ImageLi150S mystery carb debris by John, on Flickr
ImageLi150S Jetex filter clean by John, on Flickr
ImageLi150S fuel oil leak cylinder base at stud by John, on Flickr

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Doom Patrol
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Sun Jul 22, 2018 6:36 pm

Have you got a long range tank fitted? It's possible to get oxidisation from the welds and that produces something very like sand in your carb.

johnny650
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Sun Jul 22, 2018 7:16 pm

Doom Patrol wrote:
Sun Jul 22, 2018 6:36 pm
Have you got a long range tank fitted? It's possible to get oxidisation from the welds and that produces something very like sand in your carb.
no just the original tank but there is some surface rust in there when I cleaned it out the other day although it doesn't appear to be loose.

This residue is like I say burnt paper. it has no thickness that you can feel between your fingers. It just disintegrates completely when you touch it. very strange . :?

johnny650
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Mon Jul 23, 2018 6:48 pm

well here is an update to the intermittent starting and rough running problem .

Its debris in the carb fuel bowl again ?
last night I stripped the carb and cleaned it thoroughly finishing with the compressor blowing every part and jet carefully. You could have eaten your dinner off that carb.

Today after it standing 20 hours I attempted to start the engine again and it was not having it. So I have decided to strip the engine and replace the leaking drive side oil seal and lap the crankcase mouth to cure the leak around the stud base and guess what I found when I stripped the carb !???... more black bits ...

Then it dawned on me where they were coming from .. Its the gasket breaking down and disintegrating presumably due to contact with the fuel. It must have some rubber or something similar in its constituents. No wonder the previous owner couldn't get it to work which is why I got it so cheap on ebay .

Has anybody come across this before ?
ImageLambretta disintegrating fuel bowl gasket bits by John, on Flickr
ImageLambretta fuel bowl gasket disintegrating by John, on Flickr

Chris in Margate
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Tue Jul 24, 2018 3:09 pm

I am surprised you believe an online filter to be "obligatory". My experience of them has not been good. I've just stripped my carb after 1000 miles and not a speck.
I have stripped filters out of Lambretta fuel lines that had starting issues after taking advice from others. You might just be surprised.

johnny650
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Tue Jul 24, 2018 10:00 pm

you're right I would be very surprised . The only times I've had starting and running problems with my Li150S is through fine sediment blocking the carb jets .
Since installing an inline filter I've not had any further problems.

Surely you are not suggesting that the crude inbuilt filter of the 18- 22mm Delorto and Jetex carbs are adequate to filter fine rust particles that our 50+ year old tanks invariably contain.

I think you night be referring to those minute 15 --20mm diameter filters folk fit. I use 45mm dia filters which also function perfectly well on my twin 38mm carb 650cc Yamaha

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HxPaul
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Tue Jul 24, 2018 11:43 pm

Its not the gasket breaking down,it looks like the float bowl leaked at some time so somebody has put sealer on the gasket.

Chris in Margate
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Wed Jul 25, 2018 7:45 am

I.have a long range tank (5 yeara)and.new tap and.the filling area is OCD clean
No rust and.no.muck.

dirtyhandslopez
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Mon Jul 30, 2018 2:03 am

HxPaul wrote:
Tue Jul 24, 2018 11:43 pm
Its not the gasket breaking down,it looks like the float bowl leaked at some time so somebody has put sealer on the gasket.
Absolutely.
That's not going anywhere...

johnny650
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Wed Sep 26, 2018 12:28 pm

apologies for not updating this thread and leaving it without some sort of conclusion.

i am still having issues starting and it seems to be a fuel supply issue. After leaving the scoot all night the fuel pipe fills with air which then causes an airlock preventing fuel getting to the fuel bowl.

Once I empty out the air and refill the pipe it generally starts but occasionally I still cannot seem tom get fuel through to the engine. ?

When it goes it goes like stink which is all the more perplexing .
I need to find out where the air is getting into the fuel pipe and why it is not venting out and the scoot should then start and run properly.

Because of this issue I would now recommend that clear fuel pipe is used so that any air in the fuel pipe is immediately apparent particularly if you are troubleshooting a no start issue like me

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