SR 175 kit gearing

[Roey99]

Hi Guys,

Could I ask for your thoughts on this one.... I'm at a bit at a loss.

I recently rebuilt a '76 Spanish Li 125 that had been in bits in boxes for the past 20 years in a dusty shed.
I've restored a few in the past so I'm quite happy with this kind of project.
I've gone for the rat look, but mechanically spot on.
It's back up together and MOT'ed , rides well BUT....

It's topping out at about 40-45 mph.

Let me outline the spec -
I rebuilt the engine from a pile of parts, new bearings seals etc with a SR175 top end, Italian piston with the head. Inlet and exhaust all matched and the ports smoothed and finished nicely by a professional local to me in Notts.
The exhaust is a JL expansion unit dating from the late 80's early 90's in good condition, the carb is a new PHPB 30mm dellorto nicely set up giving me a chocolate brown spark plug across the range.
Electronic ignition fitted, strobe timed it ticks over and revs nicely.

The gearbox that came with the scooter was an Li 125 box with the low first gear.
Initially built this with the 46 x 15 gearing and got a ok response through the gears, but it was done at about 45mph on the clock.

I had a look at the gearbox chart posted up on the CAM LAM website which shows all the different options and set ups.
A 47x18 set up with the Li 125 box should give a ratio set close to that of the TV175 .... tried that - but no it's slower than before !

The old girl runs well and starts first kick - before I start to change things around again - any thoughts on the way to go ?
My next move was to swap the 18 tooth sprocket for a 16 keeping the 47 at the back - anyone done similar and had good results ?

I'm not looking for a rocket ship - 55 - 60 mph and reliable is the aim - any thoughts or suggestions on a route forward ?
I'd like to keep the cost sensible and use the gearbox I have.... but I might have to re think that.

Thanks in advance - jr

[dickie]

Sorting the gearing assumes that the engine is correct.

What's your compression like? Port timings? Is the pipe clean? It could be coked up.

[camel]

Youve overgeard it....16 or 17 max front sprocket...id go 16....i run a 17x46 with that box on a sil200,30 carb and a taffspeed pipe and it just about pulls it so you have no chance with a 175,basically you havnt the power to pull fourth gear into its power range.

[Fast n Furious]

Can you feel a definite power band as you go up through the box? If you're not feeling it in 1st 2nd and 3rd, then it will die in 4th.
Unfortunately it could be due to any number of things to do with your engine tune. Those early JL's never did it for me though.
Measure your speed with a Satnav. The lammby clock knows no accuracy and usually lies better than a fisherman.

[Roey99]

Thanks guys,
Yep, no power band through the gears and yes it's very flat in top.

The top end came from Scooter resto's, so it's a good quality part, not an eBay cheapie.
The piston, head and barrel all went to the old school engine builder to be sorted, he's done these kits for quite a few others and they are cool.
I'm thinking top end is ok.....compression etc all seem fine.
Almost feels like it isn't able to rev out beyond a certain limit to get the speed built up.

I could give the exhaust a de coke - any thoughts on the best way to do this with chemicals from Wilko's ?

Gearing needs a closer look.... so I'll get the 16 tooth sprocket and chain selection out and give that a go I guess and then try it on the road.

Will update as I get a moment to change the gearing. jr

[bluebob]

Before you start changing gearing I would try a clubman type exhaust .as previously said,you haven't got the power that your exhaust needs.you will see a massive difference.

[Phil D]

Reading with interest as I've been reading up on the SR kit 175/185 as I've got a NOS barrel myself.
I run a 46 /16 front sprocket on my cast iron 175 -22mm jettex ,42 clubman.
I went from a standard 15 ,pulls great 1,2,3 but just lacks enough power to really pull 4th .
I think I've reached the end of the road with mine only thing that's putting me off is it's been really reliable.


it's not really been an issue up to press doing local

Ride outs etc ,but I'm wanting to get a bit further afield and I think it's a well worn path most people take.

Interesting that it was no good with TV175 gearing as the reading I've done says the kit was originally based on TV 175 timing.

[Roey99]

Thanks BlueBob, I'll have a look into the clubman exhaust idea ..... I think it's well worth a try.

I'll leave the basic gearing as it is for now because the CAM LAM data suggests that it should work ok with the gearbox i have and the 175 top end.

Time to see which Clubman is the best deal I guess, the tatty old Indian one I have on the GP from Scooter resto's has lasted well, maybe that's my first port of call, anyone had any good / bad experiences with other types of clubman exhaust ?

Cheers guys

[MickYork]

When you say a JL exhaust, that can cover a multitude of variations, a JL4 is a different exhaust to a JL3. etc.

I'd try a different exhaust (as suggested).

[Roey99]

The exhaust - Its a really early one only a date and "Lambretta 125-200".
It's probably a collectors item.... but it's not doing the job for me by all accounts.

I think I'm going to go with a 16 tooth front sprocket with a 47 rear sprocket if I find a chain in the spares collection to match it all together.
I'll probably look at a clubman from AF Rayspeed and give it a try.
Seems sense to drop the gearing slightly before fitting the exhaust, otherwise I pretty sure the exhaust would need to come off again after the first road test to tweak the gearing again...

Let's see where we go with this set up.

Be great to be able to enjoy riding this one, based on it's 20 years sleep in a shed.

Thanks for your help !! - jr

[bluebob]

I misread your original post,and agree it would make sense to change the gearing.that final drive could probably do with raising to 5.2 ish. I ran my old 185 on pacemaker box,46/16 giving final drive of 5.3 and could not fault it.very quick acceleration topping out high 50s.,along with 42mm AF clubman.have read on here somewhere that the scootopia clubman's are very good.Good luck with it.

[Roey99]

Cool - thank you.

If I get the time this weekend I'll make a start.

Need to have a closer look at the exhausts on offer too, be good to put a clubman on the scooter, this JL is very loud.

jr

[Roey99]

Thanks guys..... the scooter is good to go !

I've taken your advice guys and fitted a Scootopia 42mm clubman exhaust and swapped to 16x46 on the gearing.

Totally transformed and feels like a different machine - rides well and it's pulling well in top.
I haven't given it too much of a thrash as I'm running it in, but 50-55 on the clock felt good and the power delivery and torque curve spot on.

Impressed with the exhaust, the split U bend makes all the difference, as expected it's a quality piece of kit.

Good learning curve for me, thanks again for your sage advice.

Roey.