LCGB Forums

I have a 225cc iron cylinder kit for my mostly standard SX200. Yet to be fitted.
The kit includes a new 70mm piston, a 225 squish head and a Jerex 22mm carb. The petrol tap is a fast flow type and I intend to use the standard air filter with a de restricted air scoop. A new clubman exhaust is fitted.
What, if any change in performance can I expect? The scooter is intended for normal road use.
Advise please for jet sizes, plug and ignition timing, thickness of gasket or compression ratio.
Trevor S

hi bud, presuming you're using an electronic ignition? then I'd go for 17deg BTDC
Thickness of gaskets depends on engine case, barrel, head, piston to transfer/exhaust port heights, & piston to head squish.
jetex:- I'd open up the float hinge hole & add a red tipped plunger, start with gp200 jets but mabes go up to 48/50 on pilot, use a delly atomisor, & main jet from 125 to 132-ish
scrap the std air filter & get a breathe sweet & drill some more holes in airbox, get rid of air box internals & get an armadilo airhose (or equivalant)
that should keep you going for now

Thanks for the information. As the scooter is so original I want to be able to fully reverse back to 200cc at some point.
The Jetex is 22mm up from 20mm so, I don't think heroic modes to the air box is nessesary. Fitting a 30mm carb certainly would.
So, fitting what I have what can I expect: more pulling power, higher rev's or no measurable change?
Having followed all the 2 stroke tuning advice of the 60's on a series 1 Li 150. I asked a engine race tuner for his advise "fit OHV" he said!
Trevor S

I did something similar with my SX200. I replaced the top end with a SIL200 which I had lightly tuned as the article Bang for Buck a few years ago in scootering. Followed by a scootopia 22 carb, with a ram air filter and their 42mm clubman. I used the ram air filter rather than butchering the SX airbox. I started off with GP200 settings, ie 45 pilot, 50 choke, standard slide and atomiser ( 7895-1 & 5899-2) and 125 MJ. But on first run, it was way too weak. After a few plug chops, settled at 140MJ, but after running in, I'm down to a 135MJ.

New SIL 200 top end with paper base gasket and 0.75mm head gasket, squish 1.2mm

I've got a variable ignition on this (Kytronik), which in reality is not necessary, but it was spare. But if going for static, I'd stick at 18 degrees

But this set up, with carb, top end and exhaust has made a big difference to performance. Saying that, the previous set up was poor and I could only get 6000rpm or 60MPH flat out with no wind. In this new set up, I've not really pushed it yet, but I bet I can get nearer to 70 mph, with a lot more torque and acceleration.

So I guess with your 225, I'd go for 140MJ as a starter and ram air filter.

Hi Paul,
Thats a nice bit of insight. I'm hoping for a bit more grunt rather than speed. It would be nice to climb hills in
top that would normally taken in third while two up.
I think I would follow your lead on jet sizes. Does anyone bother to raise crankcase compression any more?
Trevor S

cos we dont have 4* anymore & we have to be mindful of the heat in the combustion area due to this sh*t fuel, nowadays we work to our ignition timings & piston to head squish bud

The 60's "regular" we ran on, and indifferent 2 stroke oil or Castrol R has thankfully long gone. E may well improve performance, it just screws up everything it comes in contact with.
I'm happy to play with plug heat rang and the massively improved 2 stoke oil. I have taken note of the suggested jet sizes - sound good.
My friend had a 150 Li bored out to 200. it went like a rocket but it would locked up. It was so predictable, once the clutch was pulled in for a few moments off it would go again. I'm pretty sure it was fuel starvation, weak at full throttle (standard fuel tap) and a heated up cylinder head.
Trevor S

Trevor S wrote:The 60's "regular" we ran on, and indifferent 2 stroke oil or Castrol R has thankfully long gone. E may well improve performance, it just screws up everything it comes in contact with.
I'm happy to play with plug heat rang and the massively improved 2 stoke oil. I have taken note of the suggested jet sizes - sound good.
My friend had a 150 Li bored out to 200. it went like a rocket but it would locked up. It was so predictable, once the clutch was pulled in for a few moments off it would go again. I'm pretty sure it was fuel starvation, weak at full throttle (standard fuel tap) and a heated up cylinder head.
Trevor S

Wonder how thin the spigot was

probs why it kept seizing it'll being wharped to f**k

Hello hullygully,
Back in those day's we were destitute students (no loans in those days). If they ran we continued to use em.
No money to fix anything. For example, I often rode to college with a broken clutch cable - no problem.
A broken clutch cable and broken throttle cable was a bit more of a challenge - not to be recommended.

Back to jet sizes: What is it I want to achieve from my bog standard SX200? It would be nice climb a third gear hill in top rather than up the MPH.
Before I fit the 225cc barrel and head and 22mm carb. Its clear I need to go back to basic principles and measure compression ratios, piston/head clearance etc. Next summer project now.
Trevor S

I really wouldn’t bother with the jetex carb more trouble than they are worth imho.

Back to jet sizes: What is it I want to achieve from my bog standard SX200? It would be nice climb a third gear hill in top rather than up the MPH.


I’d be looking at your gearing if you want too achieve bill climbs in top gear

is your gearbox a std SX200 bud?
try a 47T clutch sprocket first to see if that improves your 4th gear.

Hello hullygully,
I will take your advice and look at front sprockets.
The scooter is still not on the road.
I applied for the registration back in March last year. after 5 months sent the DVLA a (gentle) reminder asking
if the documentation may arrive before summer was over. It took another month for them to turn down my
application. I re applied. A letter was also sent by the Lambretta Achieve chap who pointed out they were not
following their own rules. The original registration came back in the return post.
So, to continue!
Trevor S