A lesson learned.

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EddieStone
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Joined: Mon Aug 17, 2015 4:13 pm
Main scooter: Lambretta Li 150
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Mon Oct 11, 2021 1:04 pm

This is a bit of a saga, but worth telling I think to show how problems can arise with a Lambretta. I've posted this here just in case it's helpful to someone that may have the same problem without realising it.

My Li150 hasn't been used much over lockdown, but a while ago I noticed a pool of fuel under it. Checked and tightened the hoses, checked it the next day - another pool. Turns out the 60 year old fuel tap has finally give up. No problem, I am a well prepared scooter rider and I have a spare....somewhere.

Tap found, fitted (eventually) and no more fuel leaks. It sat there for a few more months, not leaking.

Out for a ride with Ms Eddie Stone and on a fast bit of road it seized briefly. More than a bit puzzled I yanked the SH2/22 carb off and checked the jets. Blew them out, refitted everything and off we go. It's not the same as it was, but pootling around it's sort of OK.

After some checking, it seems to be getting hot with another very light seize. Puzzled I check the only thing that's changed recently - the fuel tap. Barely a dribble. Well, a bit of a dribble. There's the problem, poor fuel supply. Scooterotica tap ordered and fitted. Fuel gushes out of this puppy. All back together and more riding. It's still not right - it won't come off the chock properly and hot at high speed. So off I go down the re-jetting road figuring the extra fuel supply has upset the jetting somehow (?!). What a pita on SH2. Re-jetted, change of atomiser and idle jet and it's working, but not really ticking over at all well and won't seem to adjust. I strip the carb off it to check and clean the airways. This is where I see the line where the manifold sits in the carb, in the nylon bush. It looks like it hasn't been in far enough to cover the two slots cut in the nylon sleeve. . . It's been leaking air through it.

I rejetted the carb to as it was originally, then tapped the carb home fully, and there you go. One nicely running scoot that starts, ticks over and runs fine. And has a new fuel tap.

So, lesson learned when considering jetting the carb - make sure it's fitted properly.

Fuel or fool, you be the judge...

Warkton Tornado No.1
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Main scooter: Lambretta SX200
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Mon Oct 11, 2021 7:35 pm

Well done! Being methodical is what solved the problem.

However, despite fitting Scootopia's excellent taps to two machines, I believe in stripping them first. There was no big issues with either, but one had a slightly kinked sealing face gasket - sorted with boiling water - but both had slight burrs on the port holes.

Of course, it's a sensible thing to tune the amount of reserve to individual taste, so I tend to fit a slightly larger diameter tube, usually made from broken radio telescopic antennas, which also have bigger bores than the standard tubes..

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EddieStone
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Posts: 428
Joined: Mon Aug 17, 2015 4:13 pm
Main scooter: Lambretta Li 150
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Thu Oct 14, 2021 11:23 am

I'm more than happy with the fuel tap, it's a significant improvement on the first replacement one.

Most of the problem was not pushing the carb fully home on the manifold, and air leaking in through the slots in the nylon sleeve. Obviously rubber mounted carbs don't have this problem.

I think when you're sorting out jetting on these carbs there may be a tendency to not push them home fully so it can be removed easily in case the jets needs changing (again). But if air is leaking in, it'll throw your jetting out, and give you a different result each time.

I posted this in case someone is having trouble setting up their SH2 carbs and may be doing the same thing as I was. I now tap the carb fully home using a block of wood, and remove it by drifting it off with a length of wood from the other side. I know the manifold is then sealed properly.

Having said that - it bloody conked out yesterday evening in heavy traffic and would not restart. The plug was heavily sooted and a new one got it going, but I need to lean the mix quite a bit now the carb is seated properly.

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