Thirsty TV175

[jaco]

Is there anyone who can advise what to do. I have a TV175 2nd series. Standard head and cast iron cylinder, Casa Lambretta electronic ignition and new oil seals.
It was running on a SH1/18 carburettor with Li150 jetting. Top speed 70-90 km/h depending on wind direction and heavy fuel consumption.

Last week I installed a SH1/20 carburettor:
Main jet: 108
Pilot jet: 50
Choke: 50
Diffuser: 5899-1
Slide: 5914-1

No change at all, still average top speed in 4th gear of 80 km/h and a fuel consumption of 13 km/litre.

I didn’t find any petrol leakage that could explain the fuel consumption.
After ½ to 5/8 throttle there is no further acceleration.
The diffuser is not correct for the SH1/20, but could it explain the poor performance and heavy fuel consumption.
I changed the main jet to 112 and 115 but didn’t notice any difference, should I try to change downwards.
Same problem with both carbs, could the problem be something else?

[bristolmod]

TV175 S2 is identical to TV175 S3 apart from the carb

As you have put a S3 carb on, then jet it as follows:-

Slide 5914/1
Atomiser 5899/2
Main 106
Pilot 50
Starter 50

run it and then report back on consumption/ performance.

Is your timing correct??

Chris

[Pepot]

Isn't the casa lambretta ignition like the varitronic? If it is, then the advance at idle must be set at 25º since it retards about eight degrees when reving. As Brystolmod has already said, I'd check the timming.

[jaco]

I don't have the right atomiser, any advise how to get it. I tried at Scooter Centre, they don't sell it because they don't have a supplier.
Does anyone know/can explain if the use of atomiser 5899/1 in stead of 5899/2 could cause the heavy consumption and low performance.

The casa ignition is like the Varitronic. It is set at 23 degrees at tick over, it retards to approx. 15 degrees at full throttle. If it makes sense I can adjust it a little more, could such a minor adjustment have such an impact?

[Pepot]

The casa ignition is like the Varitronic. It is set at 23 degrees at tick over, it retards to approx. 15 degrees at full throttle. If it makes sense I can adjust it a little more, could such a minor adjustment have such an impact?

Yes. Two degrees are not a minor adjustment. In fact is the difference between the original setting and the recommended advance for unleaded petrol.
I had a similar problem with a standard LI 150 and a varitronic. Lack of speed and poor acceleration at a certain regimes. Setting the advance at 25º at tick over solved the problem. I wouldn't spend any money in carb jetting till you try this, since is a costless test.

[wack 63]

You can try as many bigger main jets as you like but the atomiser will only flow what it's bore allows. Allstyles sell a remade 5899-2 and Scooter Restorations have the jetex version. I would definatly change the atomiser but also advance the timing . Your standard cylinder was originally set at 23 degrees and if it is revving out in 4th around 7k then the timing would be at 16 degrees but you would probably be better setting it to a safe figure at your chosen cruising speed

[jaco]

Thanks for all the good advise. I'll keep you informed about the results!!

[jaco]

I made the adjustment of the ignition timing. No improvement on fuel consumption nor top speed yet.
I am still waiting for the supplies of Allstyles. I hope the atomizer will make the difference.

[Pepot]

What is now the timming at idle?

[jaco]

The timing at tick over was changed from 23 to 25 degrees.
Today I installed the 5899-2 atomizer I received from Allstyles. No big improvements yet.
The next thing on my list to change is the exhaust...