Scooterotica

Personally I would upgrade the carb too either a phbl or phbh, and you will certainly notice a difference. IMHO it would be money well spent.

Good luck with it, hope you get the desired solution.

I am curious as to why it had an 18mm carb on.

What else might be different?

Brakes binding ?

Front drive sprocket not tightened down correctly and rubbing on chaincase?

What colour is the spark plug?

Is the choke sticking on?

Are the air filter and airbox clear ?

In my opinion I do not beileve spending hard earned money at this point on a non standard carb will improve your mpg or kmpg.

What is the state of the cylinder bore and rings?

If you are not leaking petrol then you are burning it.

90 kph is about right but you.should get at least 20 km per litre
A few more basics that I would be checking

BTW you don't happen to weigh over 25 stone (260kg), do you?
Good luck

I bought it about 10 years ago from a man who did a cosmetic restoration. He had several Lambretta's and never ran it because it was not registered yet. The scooter was not running. At the time I bought an old barge to build a houseboat so the scooter was left like it was until last year.
I got it running by cleaning the points and carburettor, but had problems starting when hot.

So i decided to change the oil seals. After opening the engine it turned out that the cylinder was completely worn and the clutch plates were almost flat. So the cylinder was bored up and an oversize piston installed and new clutch plates installed. Since the engine was open I decided to upgrade to the Casa electronic ignition as well.

I tried to contact the seller again to inform about the carb, but he was not living at the same address anymore. Maybe he put the original carb on one of his other scooters and installed an 18 mm on this one. I am told that the 18 mm carb was not uncommon on the TV175 in the Netherlands, maybe because we don't have hills?

The exhaust is not original. It is stainless steel and seems to be a custom made. Because the change of ignition and carb didn't do much I suspect (hope) that exhaust is the problem. Maybe the exhaust pressure is too low, causing some of the fuel leafing the exhaust unburned?
I can get a used 3rd series exhaust keeping the costs involved to try limited. Although I am in doubt to spend more and buy a new exhaust straight away.

Stuck rings would be my guess. When running-in we all tend to be over cautious and add a bit more oil in the mix (to be on the safe side !!). The problem is the excess oil doesn't get burnt as the running in doesn't generate the heat and power to get rid of the very oily residue left in the barrel. This gets into the rings and then they start sticking.....symptoms: loss of power and higher fuel consumption..........on the other hand i may be wrong !!