LCGB Forums

I have a series 2 125 motor to rebuild.

I'm in 2 minds about keeping it completely original and giving it a little bit extra.

Would fitting one of those 175 cast iron barrels work with the original MA18 carburettor or am I just wasting my time?

They can be made to work but the porting is a bit suspect on some so will need some tidying up. Dont know about the carb though, it will need up jetting for sure so availability of suitable jets is key

i rode one a few years ago back to back with my 186 Mugello and was very impressed with how well it ran, not as quick as the mugello but not that far off. That had a 30mm PHBG and a clubman and had been put together by someone that knew what he was doing (Captain Caos)

Yes, my home tuned 175 with 28mm dellorto and gori pipe went very well. I'm not looking for anything like that though.

It's mostly whether the tiny old carb can work with it properly. If I do it, I'll be keeping the ports very low, closer to standard.

I had one back in the day, originally a 150 barrel bored out and slightly tickled by Mr Barlow( pro port) 22 jetex and 48 clubman, went very well indeed. Also tried the ally/ iron sleeved eBay rubbish on my S2, again 22 jetex n clubman. Although it went well until I pushed it over 50 and would lock up.stop and let it cool down and carried on. Must have happened about 15 times or more. Still started and ran but don’t know why when I took off the barrel for a RT replacement it was a sorry looking barrel n piston. Now used as a door stop

If it was mine I'd go for a kit that is designed to work with a SH2/22 such as a Casa 185, Scootopia 185 or Gori Sport 200 (Gori has more low-end power than the other two). I'd then use a TV/2 inlet manifold with a SH2/22--they work if you change the carb bushing--that way the carb will be positioned in the right spot under the airbox and you won't have to trim the cylinder cowl. Add a Casa S2 Clubman, change the final drive ratio and keep everything else factory.

If this is too wild of a tune, the alternative would be fit a GP150 cylinder.

I have fitted several of the Scootopia 185 kits and the owners are very pleased with them.

I have built this engine to go on an SX150. I am not going to run an airbox but it does have a Scootopia remake of the standard exhaust. Keeping the standard exhaust was deliberate as they make very good power between 3500 to 4500 revs.

It’s an old original SX150 or GP150 barrel, 175 rebore and Stage 3 (very modest) tune by Chiselspeed. This was cheaper than a kit and I was pleased to be able to use an old barrel. MB inlet manifold and Mikuni TM24. AF Close ratio 4 speed gearbox with a final drive ratio around 4.9 or 5, if memory serves me right.

I have been recently running around on a standard TV175. This has good power too and has made me think that the SX150 engine I have built should work very well through the airbox with an SH1/20.

I'm becoming a bit of a fan of this kind of low-spec, easy to pootle about on stuff. However, as the bike is so original, I've decided that I'm going to leave it completely standard; 125 s2, standard exhaust, 6v, points etc.

But I'm building a 62 stroke x 65 bore with clubman and 25PHBL through a drilled airbox for when I get bored.

The Indian Alloy/chilled Iron barrel that I reworked yielded results that are potentially available to anybody, but the time involved would stop me doing one ever again. The item that I tuned sounds fairly typical that in order to align just the transfers inside (sleeve to cylinder) will result in wide ports that will flow extremely well.

The consequences of having little choice (if the transfers are 'corrected') is to improve the inlet & exhaust porting but that does not equate to 'wild' tuning, though in the engine I built there was a filtered 28 mm carburettor with an expansion chamber. I feel certain that it would have run with an SH22 but I'm not convinced there is an OEM type filter available to be unrestrictive. If I were a betting man, I would make claims via the 'seat-of-my-pants-dyno' but I will say the opinion of other testers coincided with mine.

If you can find an OEM Innocenti GP150 cylinder fitted with a good, two thin rings piston, 22 mm minimum carburettor with adequate filter & a free flowing exhaust (a gutted OEM type box with adequate tailpipe will do - no need for a large 'U' pipe), optimise the porting, squish, head volume etc with very little retardation of ignition, the result can be a sparkling engine with good economy & the capability to over-rev. A 'J' range flywheel weight would be ideal for those seeking the reassurance of reliability that points ignition offer..... Now, that's one bet i would make! Comparing ignition system reliabilities.

dickie wrote:I'm becoming a bit of a fan of this kind of low-spec, easy to pootle about on stuff. However, as the bike is so original, I've decided that I'm going to leave it completely standard; 125 s2, standard exhaust, 6v, points etc.

But I'm building a 62 stroke x 65 bore with clubman and 25PHBL through a drilled airbox for when I get bored.

You'd got my interest up to:

"But I'm building a 62 stroke x 65 bore"

It all went downhill after that.....

Warkton Tornado No.1 wrote:
You'd got my interest up to:

"But I'm building a 62 stroke x 65 bore"

It all went downhill after that.....

I know why you don't like it, but I've got the parts on the shelf so.......

Good replies given so far.
I also like low end tunes. Any combination with a 60x115 crank, 22 Dellorto with drilled Airbox, standard exhaust. I do like using Suzuki TS185 pistons. Cheap SR Indian barrels can be reworked with porting, honing and a reprofiled head. Standard ignition set to 20 degree.

GExS wrote:Good replies given so far.
I also like low end tunes. Any combination with a 60x115 crank, 22 Dellorto with drilled Airbox, standard exhaust. I do like using Suzuki TS185 pistons. Cheap SR Indian barrels can be reworked with porting, honing and a reprofiled head. Standard ignition set to 20 degree.

I have a TS185 new piston on a shelf and the 150 barrel off my winter model, three fins below the exhaust port.
Do you know where I might get it bored out to take the 185 piston ?
Have the RT195 kit on the winter model and this spare cylinder is for another project if it's a viable option.

I had this done a few months ago Duncan. Any decent rebore place should be able to do the job but it takes quite a few passes to get the bore up to size, luckily I was able to get a good price thanks to my mate trading work time, otherwise it would have cost quite a bit more.

Mark

I've got an sr175 barrel that had been bored to take a mitaka suzuki ts185 piston. I'm pretty sure I have a head top match too. If anyone wants them, they're for sale cheap.

No porting done.

Solid Air wrote:I had this done a few months ago Duncan. Any decent rebore place should be able to do the job but it takes quite a few passes to get the bore up to size, luckily I was able to get a good price thanks to my mate trading work time, otherwise it would have cost quite a bit more.

Mark

This is what I have found out.
I am in Spain and took the piston and cylinder to two engineering shops and both of them were not interested in the job for the very reasons you mentioned.
Lot of time making many passes to open up the bore.
Even pushing for any idea of cost didn't get me anywhere.
It would appear that I have a nice new piston on the shelf and it's going to be staying there.
Work out cheaper and better in the long run to get a 175/186 cylinder kit .
Shame as I was looking forward to playing around with the short cylinder .

duncan1958 wrote:

Solid Air wrote:I had this done a few months ago Duncan. Any decent rebore place should be able to do the job but it takes quite a few passes to get the bore up to size, luckily I was able to get a good price thanks to my mate trading work time, otherwise it would have cost quite a bit more.

Mark

This is what I have found out.
I am in Spain and took the piston and cylinder to two engineering shops and both of them were not interested in the job for the very reasons you mentioned.
Lot of time making many passes to open up the bore.
Even pushing for any idea of cost didn't get me anywhere.
It would appear that I have a nice new piston on the shelf and it's going to be staying there.
Work out cheaper and better in the long run to get a 175/186 cylinder kit .
Shame as I was looking forward to playing around with the short cylinder .

The majority of material removal could be done on a lathe, leaving a safety margin for boring/honing. I wouldn't recommend attempting the whole job on a lathe, though it has been done.

I suppose P&P costs would be prohibitive in sending it here, but there will be somewhere in Europe making it a more viable option. The likes of Jim Lomas might be able to help you with some suggestions, or the German Forums are very active.

.[/quote]

The majority of material removal could be done on a lathe, leaving a safety margin for boring/honing. I wouldn't recommend attempting the whole job on a lathe, though it has been done.

I suppose P&P costs would be prohibitive in sending it here, but there will be somewhere in Europe making it a more viable option. The likes of Jim Lomas might be able to help you with some suggestions, or the German Forums are very active.[/quote]
I have flights booked for November and could bring the cylinder and piston with me and post it to someone who is capable of doing this in the UK.
Not in any major rush to build the engine.
Next visit due March of 2022.
Recommendations as to who would be best to contact about this type of thing will be greatly appreciated,perhaps a separate post on the forum asking for help might be better.