SX150 carb / exhaust / gearing question.

[corrado]

Rebuilding an SX150 engine which I'm going to go 12 volt ignition with GP crankshaft. Using a new Indian GP150 kit and was planning on going 20mm carb with standard exhaust or should I opt for 22mm carb with Scootopia Ancillotti? Looking at probably using Indian GP200 gearbox, 18 x 47 for 5.2 final drive. Original SX gearing would have been 5.65 final drive in 4th so I'm a bit worried that 20mm and peashooter won't pull 5.2, though only carrying 10 stone will work in my favour. A major factor of the build is the sound, so it's a small carb through the airbox, bigger carbs / kits / etc are not under consideration. It's going to be option 1 or option 2, no other options necessary.

[missing lynx]

They only used a 20 mm on the tv/sx 200's

[Adam_Winstone]

I had a wonderfully performing standard Italian GP150 that I used for a number of years and the ease with which it pulled 5.7 made me sure that it would pull 5.2 (LI 15/46), however, it was an error on my part. It went from a great all-rounder that had no issue reaching the 'sweet spot' and staying there but turned into a hard ride that only ever really pulled 4th correctly on a long downhill straight (1-up). 2-up became a real chore and it was no more than 2 weeks before I summoned up the enthusiasm to go back to the original gearing.

FYI - Around the same time a fellow clubmate had an original SX150 and we would regularly ride together to our weekly club meeting. The GP150 and SX150 matched each other stride for stride and the GP had ZERO more top end. Yes, I know the 60s tuning manual suggests a little more rev-on for the GP150 but it also shows the same peak BHP figure. On the road they were equal, regardless of 2mm bigger carb on the GP.

Adam

[corrado]

Thanks Adam, exactly what I suspected but didn't want to hear.

I had similar experience with my Imola, it was spot on with a ScootRS exhaust and 5.4 gearing and would fly up most hills in 4th. When doing Le-Jog I thought it would benefit from taller gearing given that it was going to be about 80% motorway riding, so I fitted a JL3 (less revvy I thought) and opted for 5.00 final drive sprocket set up, surely it would cope with that, alas within a few miles on the motorway I had to drop into 3rd gear because of a mild headwind, and any incline was now 3rd gear half the time. I'd figured that if an SX200 with 9 bhp could pull 4.8 then surely an Imola with 16 bhp could cope with 5.00 ....... wrong.

One of my problems is that I've never actually had a standard engine, even my first scooter was a GP150 with 175 kit. That ran well enough with GP150 box and 16 x 46 but hit a brick wall at 55.

How did the Li150 ever cope with Li150 gearbox? Or didn't it, as Specials / SX150 and GP150s were subsequently fitted with shorter gears.

I'm trying to avoid building an engine that struggles to get much over 40 mph and yet I still want to build it as original as possible. Using a 20mm carb as I can't buy a new 18mm version. Cost isn't a factor either.

[corrado]

They only used a 20 mm on the tv/sx 200's

I'm only planning on using a 20mm because I can buy a new one but I can't buy a new 18mm.

[Adam_Winstone]

Standard LI150 is a plodder and didn't give great performance. When you consider that the same ratio was used for Innocenti GP200 and Stg. IV SIL 200, the GP/SX150 will always struggle to pull it.

[corrado]

I've been playing about with various set-ups on Tony Cassidy's gearbox visualiser and I've come up with a feasible plan. I've got a close ratio g/box that is based on SX200 1st, 2nd & 3rd gears with Li150 4th gear, with 15 x 47 cogs it'll give 5.33 in 4th gear and 52mph at 5475 rpm, I'm hoping that a tall 1st gear won't be an issue but that apart the ratios are close together which should help it maintain the revs in 4th.

With a GP150 kit what is the main factor in it's lack of revs? The barrel porting, the small carb, the small exhaust or more than likely the combination of all 3. I can only summise that a 22mm carb and Scootopia Ancillotti clubman may help slightly with the revs but tuning a barrel isn't within my skill set apart from matching the flow on the inlet manifold and exhaust port.

Any thoughts?

[jonw]

Is a 5 speed box a consideration?
I started a thread a couple of years ago to gauge if anyone was running a 5 speed on an original 150 or 200 to which Nudger replied confirming what I suspected.

Reply below.


Re: Cyclone on a standard engine
Postby Nudger » Sat Jan 02, 2016 6:47 pm

I've got a 'standard' Li 150 Special (18mm carb & standard barrel/piston, GP crank/electronic kit + Clubman).
She's been running with the Cyclone gearbox now for a couple of years+ & I've never had a problem with it yet. On the road she has shown a top speed (GPS) of 59.8 mph & has quite a pull uphill: the torque in this motor showed a clean pair of heels to friends when we hit a few steep sections on the way to the Euro Lambretta in Switzerland.

On the flat she can cruise all day at around 55 mph without feeling as if the engine is really straining or over revving at all. That's what I really want & in due course when a re-bore is required I'll just pop on a 22mm carb & take her out to 175cc.

I know these kits are expensive & not to everyone's taste, but my personnel experience has been a good one & the ride is very nice.

[Scooter Paul]

A few years ago I recommissioned a SX150 for a friend. A genuine 5000 miles from new and unused for 40 years. It was carefully stored it looked like new. I kept it 100% standard. I just replaced all the oil seLs and clutch cork plates. What was such a revelation was how nice it was to ride. Smooth, quiet and by no means slow. There’s a lot to be said for keeping them stock.

[jonw]

My son has an original paint, low mileage S3 Li125 which we fitted GP150 top end, 22 Scootopia carb and AF clubman. It also is an absolute joy to ride and pulls from nothing. He did the C2C on it with our group and it only showed its limitations on the A1.

[Nudger]

An update to my comments above made three years ago (where does the time go?!): a new piston + rings last year and that's it. Everything else is still working nicely and I'm looking forward to riding her to Poland. The Casatronic kit and Cyclone remain faultless. I've been lucky enough to win a Uni casing on the SLUK site & I'll build a new engine; I'm not touching this one.

[jonw]

You lucky boy!

[corrado]

A few years ago I recommissioned a SX150 for a friend. A genuine 5000 miles from new and unused for 40 years. It was carefully stored it looked like new. I kept it 100% standard. I just replaced all the oil seaLs and clutch cork plates. What was such a revelation was how nice it was to ride. Smooth, quiet and by no means slow. There’s a lot to be said for keeping them stock.

That's the dilemma, I want to keep it as stock as possible, but many parts are missing and I'm going to have to use new parts, crank, gearbox and ignition among them, so if I need new ones I may as well future-proof it with 12 volt and GP crank. I've never had a standard engine but recently had a little "car park" ride on an SX150 and I was blown away by the feel and sound of it, but for modern traffic it needs to be capable of doing in excess of 50mph.

I hadn't considered a 5 speed box, so you've thrown me another curve ball into the mix.

[corrado]

An update to my comments above made three years ago (where does the time go?!): a new piston + rings last year and that's it. Everything else is still working nicely and I'm looking forward to riding her to Poland. The Casatronic kit and Cyclone remain faultless. I've been lucky enough to win a Uni casing on the SLUK site & I'll build a new engine; I'm not touching this one.

Any ideas of your gearbox ratios?

[Nudger]

5th gear ratio is the important factor & mine is 4.72:1 if I remember correctly

[Scooterslag]

A few years ago I recommissioned a SX150 for a friend. A genuine 5000 miles from new and unused for 40 years. It was carefully stored it looked like new. I kept it 100% standard. I just replaced all the oil seLs and clutch cork plates. What was such a revelation was how nice it was to ride. Smooth, quiet and by no means slow. There’s a lot to be said for keeping them stock.

+1 on this, been running about on a standard SX150 for the best part of 25 years and despite struggling a bit on busy duel carriageways /short motorway sections - it has always held its own and keeps up with modern traffic fine. Reliability and fuel economy are a bonus as well. Paul