LCGB Forums

I've got a Rapido 225 race with a jet 200 gear box and 16/46 sprockets. 30mil Delly carb. I have a JL3 exhaust fitted. Tops out at 60mph and has nothing left. Should I refit the 48mm clubman? Or are there better exhausts to get the power out of the kit?

49 mm carb?. I ran a rapido 225 classic will a 26mm delli and sterling exhaust with std indian gp gearbox and front and back cog it had bags of torque and would top out just over 70

I have ran several Rapido cylinders in my time & in full race tune with only a 66 mm bore, they are capable of over 90 mph.

On the road, my opinion is that the 'race' cylinder (I have never seen a 'road' version) is best fitted with a longer stroke so that the tuning can be tamed. A 60 mm stroke crankshaft is going to be less money than yet another exhaust, but 61 or 62 mm would be even better. My SX 71 mm x 61 mm home tuned set up with a DIY 38 mm 'Clubman' pulls TV200 equivalent gearing fuss free from town speeds in top. I have no tachometer or GPS fitted but I reckon more than 80 mph is available. I'm sure there are better set ups than mine, but 'optimising' is what it's all about.

I cannot comment about n the options of exhaust you state, other than a Clubman exhaust needs a bleed (tailpipe) diameter of @ least 25 mm for that capacity.

Something doesn't sound right, gearing wise sx200-46x16@4.5 @ 60mph would mean it's only only revving to around 5800rpm, with that pipe and the high duration of the exhaust port on rapido race, should hit around 7500, it's more likely over geared if anything and possibly struggling to hit peak power.

missing lynx wrote:49 mm carb?. I ran a rapido 225 classic will a 26mm delli and sterling exhaust with std indian gp gearbox and front and back cog it had bags of torque and would top out just over 70

Just read my post should've said 30mil Delly not 49mil. Guess I should read before posting.

dscscotty wrote:Something doesn't sound right, gearing wise sx200-46x16@4.5 @ 60mph would mean it's only only revving to around 5800rpm, with that pipe and the high duration of the exhaust port on rapido race, should hit around 7500, it's more likely over geared if anything and possibly struggling to hit peak power.

I read the Scooter help gearing chart and according to that with the gearing I have 6000 rpm should equate to approx 67mph.Getting nowhere near that.
Before I had an Indian gp 150 box and same sprockets with a 48mm Af clubman and it pulled 64mph and had bags more grunt lower down. Think I wasted time and money on the gearbox

I ran mine at 4.8 ( different exhaust) was a bit gutless up hills and into the wind but great when you got it up and held it in the revs.
You could try the SX box at 15x46 which will give you 4.8, which was the same as I ran mine Gp200 19x46
Mine topped out around 70 did well in 3rd

I ran mine at 4.8 with a BGM clubman and it pulled rearly well but topped out mid/late 60’s and wasnt a lot of fun around town.
I ran it with a PM pipe - and it freed it up on the top end but was gutless if you didn’t have it zinging along.

I bought a motor with a rapido on it and a Gori 50 Sport clubman. It rode as you describe so looked into to the gearing and it was a Indian GP200 with 20/47 (4.7) swapped to a 19 front (4.95) and it transformed the ride to what you would expect. Sat nice at around 65 and topped out at about 70.

Warkton Tornado No.1 wrote:I have ran several Rapido cylinders in my time & in full race tune with only a 66 mm bore, they are capable of over 90 mph.

On the road, my opinion is that the 'race' cylinder (I have never seen a 'road' version) is best fitted with a longer stroke so that the tuning can be tamed. A 60 mm stroke crankshaft is going to be less money than yet another exhaust, but 61 or 62 mm would be even better. My SX 71 mm x 61 mm home tuned set up with a DIY 38 mm 'Clubman' pulls TV200 equivalent gearing fuss free from town speeds in top. I have no tachometer or GPS fitted but I reckon more than 80 mph is available. I'm sure there are better set ups than mine, but 'optimising' is what it's all about.

I cannot comment about n the options of exhaust you state, other than a Clubman exhaust needs a bleed (tailpipe) diameter of @ least 25 mm for that capacity.

When I bought mine they were offered in classic or race version the classic in std trim offered more torque with a more civilised performance. I use to travel 2's up a lot of the time and could comfortably keep up with my mates mainly solo on P2's

My feelings are that for any kit to respond well, there has to be a methodical approach taken in respect of all the variables.

As a result & by keeping records of each tune that I nave done, I am comfortable with the 'constants' that I apply, such as ignition timing, squish, compression ratio & (of course ) exhaust bleed size. In many instances, such as the Rapido, you have little choice other than to try & achieve better port timings via stroking to 60 mm or more. That's not so bad if a build requires a fresh crankshaft anyway, especially if an OEM design is available, which I would prefer (see HPC below)

In all the years that I have had Lambrettas, commencing early 70's, I have gone from the doctrine of high compression, high primary compression & small(er) tailpipe in the interests of torque, to the complete opposite in many ways.

I know that there is currently a school of thought that suggests that crankcase transfer porting yields no measurable benefit, but I continue to do so because any means of reducing primary compression is to the good IMO.

Pumping losses simply because there is a HPC should be borne in mind, though I don't have the luxury of any equipment to prove what I say. However, @ the risk of repeating myself, it is a fact that two stroke engines are likely to yield gains by just adding a longer conrod with barrel packing. The other benefits of lowering primary compression & having an exhaust that doesn't gas up is that the engine is more likely to be able to over-rev without 'hitting a brick wall' & thus be safer @ WOT downhill. Just don't roll off the throttle as one MQ kitted rider learnt the hard way.......