Carb and exhaust advice please?

[Hughieboy]

Hello out there.

I'm new on the forum and wonder if anyone might be able to help me with ideas to get a bit more performance from my engine. I have an S2 Li with a S3 150 motor. Prior to my ownership it was rebuilt by Harry Barlow and is now 190cc apparently. The barrel is iron and there is a packer at the base about 2 or 3mm thick. It is fitted with a 22mm Jetex carb that runs through the air box and when I bought it it had an Indian big bore exhaust which I have since swapped for an old under kickstart Fresco (I just loved the look of them back in the 80's!). I can see that work has been done as the inlet manifold has been opened up a bit and polished where the carb fits on. It has Pacemaker gears apparently and also has electronic ignition.

I spoke to Harry once and described it but he couldn't remember the build specifically so other than sending me some jets to make it run better he couldn't offer much advice on making it quicker. He told me it should be good for 70mph he thought but the fact is it tops out at 55mph, flat to the boards.


It is reliable and runs well but performance seems a bit thwarted somehow like its holding back a bit and I want to get it to be a bit quicker all round, acceleration and top end if poss.

Does this set up sound familiar to anyone? Thing is, I don't know exactly what it is! I'm wondering if adding a bigger carb and better expansion would help, I like the look of the Gori exhausts and the fact the rear foot boards wouldn't need cutting. I believe they are more of an expansion whilst looking like a clubman, is that right? I don't need a touring type set up as I use it more for blasting about on than going on rally's.

So that's where I am. Would adding a better pipe and correctly matched bigger carb improve things or is it down to the type of tuning done to the engine.... There's no point shelling out a few hundred quid and not making any gains. And as I don't know what crank is fitted (does the packer mean it has a longer stroke?) I don't think I should just buy a kit (GT186 or Imola would be my choice, probably GT) and bolt it on either.

Sorry for the long post, it's a good runner just a bit slower than I'd like and I don't really know enough to decide which direction to head in. Any ideas anyone?

Thanks for reading,

Hugh.

[rosscla]

I'd be guessing but if there's a packer I'd expect it to have longer conrod, for 190 cc you'd probably have a 60x110 on a 65 bore.

You could stick a bigger carb on and an expansion and maybe wring another few mph out of it and less mpg.

The UKS fresco is quite a low revving pipe if I remember, long and narrowish so makes its power lower down so you don't want too peaky a tune.

Whether it's got the potential will be dependant very much on the state of tune.

[Muppet]

what he said +1

[Hughieboy]

Thanks for the advice..... The bloke I bought it from said he had paid over a grand to have the engine rebuilt and tuned, but again couldn't really tell me much about what had been done. I guess trying the bigger carb/exhaust route is the only option with this one.... If I was starting with a standard motor it would be a blank canvas for a new kit and rebuild but as money has been spent on the 'do 55mph all day' tuning it would probably be a waste to undo all the work that's been done as it would probably suit someone as a complete unit and I should start again if I want something quicker maybe...

[olliewtf]

If harry has said its a 190, then it means its probably a suzuki conversion. suzuki pistons are cheap and good quality. however the compression height is shorter than a standard lammy piston, so to compensate, it will have a longer rod. 3mm packer sounds a bit big to me though, as it will probably have a conrod at least 115mm up to 117. It could be that the barrel has been shortened top or bottom or both...
As this is all speculative, the best thing you an do is take off the barrel. measure the port timings, see what piston you have, and see what crank you have. stick it in a calculator and let us know the info. this will help massively. I run a suzuki conversion that i built and tuned myself, and it will be the opposite end of the spectrum to a barlow tune. I know this because he built my crank (60x117) and we discussed my plans. He said no no no dont do that, no no no dont do that either. I did it anyway. Harry Barlow is a brilliant tuner, and im not, but i could tell from the port timings he was quoting me, which i ignored, he's a fan of a torquey set up, which suits lambrettas and their riders very well. I wanted a screamer, and thats what i built. It worked very well, and i feel that you may be after the same thing.
Its not a case of me thinking im better than harry, he is a legend and far, far more experienced than i am. I simply wanted something different, I had a different taste shall we say.
The point here is that once we have established how your top end is running, what spec it is, we can offer advice about how to achieve what you want to achieve. it could just be that the previous owner was told on a forum, you need a 3mm packer, and in reality its thrown the port timings way off. so a 2 quid gasket could improve things drastically. it could also warrant a re-tune and new exhust / carb combo to suit.

[Hughieboy]

If harry has said its a 190, then it means its probably a suzuki conversion. suzuki pistons are cheap and good quality. however the compression height is shorter than a standard lammy piston, so to compensate, it will have a longer rod. 3mm packer sounds a bit big to me though, as it will probably have a conrod at least 115mm up to 117. It could be that the barrel has been shortened top or bottom or both...
As this is all speculative, the best thing you an do is take off the barrel. measure the port timings, see what piston you have, and see what crank you have. stick it in a calculator and let us know the info. this will help massively. I run a suzuki conversion that i built and tuned myself, and it will be the opposite end of the spectrum to a barlow tune. I know this because he built my crank (60x117) and we discussed my plans. He said no no no dont do that, no no no dont do that either. I did it anyway. Harry Barlow is a brilliant tuner, and im not, but i could tell from the port timings he was quoting me, which i ignored, he's a fan of a torquey set up, which suits lambrettas and their riders very well. I wanted a screamer, and thats what i built. It worked very well, and i feel that you may be after the same thing.
Its not a case of me thinking im better than harry, he is a legend and far, far more experienced than i am. I simply wanted something different, I had a different taste shall we say.
The point here is that once we have established how your top end is running, what spec it is, we can offer advice about how to achieve what you want to achieve. it could just be that the previous owner was told on a forum, you need a 3mm packer, and in reality its thrown the port timings way off. so a 2 quid gasket could improve things drastically. it could also warrant a re-tune and new exhust / carb combo to suit.

Thanks, that's really informative and helps me to get a better understanding of what I have.... I've just tried to better measure the packer and in reality it appears to be nearer 1 1/2 or poss 2mm but no thicker as best as I can ascertain, it's not as thick as I first thought. And you're dead right, when I also spoke to Harry although he didn't offer any specific information on what he had used he did say no, don't change the carb and no, don't change the big bore exhaust and it should be good for 70mph..... It's nowhere near that and although reasonably torquey it's not particularly free revving.... And yes, I would prefer it to be a bit more of a screamer (preferably one that doesn't go bang though!).

Regarding crank identification and port timings, having not got involved in engine work much before I don't know how to do this so will hunt around for info on here, I totally understand that nobody can specifically advise without the correct info but I would need to be sure about what I'm looking at..... After all, all though it's not how I want it to be it is good and reliable and I'd like to avoid messing it up....

Would it be worth trying a bigger carb and a better expansion first to see what happens or it that putting the cart before the horse?

I appreciate your help,

Cheers.

[olliewtf]

i think that would be putting the cart before the horse as it means shelling out a few hundred quid, far better off looking at what you have first. for example, if you have a standard piston, say indian pattern 175 piston, i wouldnt trust it to stay intact if you build something that revs higher. the problem is is that it also depends on how skilled you are at sussing what is an isnt working. youre lack of power could be coming from elsewhere, but as long as you have covered all your bases then you should be fine, ie jetting being spot on, air filter system being unrestrictive, proper gearing set up and so on. it may be worth blue printing your engine, particularly if someone else built it who you dont know or have not complete faith in, on order to ascertain if it is just the set up thats holding you back and not other contributing factors.
i think 70mph on a s2 with 175 clubman and 22mm jetex is mighty ambitious. lambretta speedo maybe, but not gps. thats the reserve of high bhp kits. how are you measuring your shortfall? because if your going by your speedo, then the good news is you dont have far to go. if, however, you go by gps speed, and you are in fact touching 60, then your doing pretty well. consider that to completely re-tune your setup including attention to engine plus carb and exhaust, based on you tuning and porting the barrel yourself, youre still going to spend a pretty penny.
If you do choose to immerse yourself in all of this, I am happy to help you every step of the way as i have been through it all myself. what i will say is it will cost alot more than you plan for, and will require fairly advanced knowledge, even if you have the work done by someone else, as factors such as ignition set up, jetting, compression etc etc become far more critical when you move away from standard, and failure to get this right in a concise and intelligent way will not only destroy expensive parts, but could also endanger you life and your pillions life. may sound dramatic but its all worth thinking about before taking the plunge!

[Hughieboy]

Thanks for your reply..... Lots to think about there! The engine was actually built by Harry, not just the parts supplied so I'm sure it's a proper job. I've had it five years and apart from nipping up once when I was running it in ( the bloke I bought it from never actually got it on the road so it was practically a new build), since getting the jetting right after speaking to Harry it hasn't missed a beat...... I just don't want keep being the bloke who rides at the front because everyone's standard Gp200/P200 or whatever is faster and I wouldn't keep up! I think if I'd actually shelled the £1000 ish that was apparently spent having the work done I'd be gutted!

But that said, I'm a tinkerer not an engineer and I'm not sure I want to get bogged down in doing my own tuning ( ie barrel alteration etc), I don't know if I have the patience to be honest and wouldn't want to cock it up. After all, it may not be how I want it but it is a solid motor.

Maybe I'd be better off getting hold of a standard engine and a suitable kit and then putting it together as recommended to take the guess work out and leave this one as it is....

Cheers.

[fastfrog]

From what i read it seems that your fresco pipe nice and sweat is killing your top power. Begin by swaping it for a big box or a gori one . Got myself this last one and ghee it pulls like a decent expansion pipe.
70 mph seems a bit tricky for a small block. 65 sounds reasonnable and reachable.

[Hughieboy]

Hmmm.... I like the idea of a Gori pipe. Maybe I could just try that and a free flowing air filter for starters and see how that goes. It wouldn't be a waste, my Fresco's a bit of a beat up old thing anyway.....