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30 BHP Cast Iron Barrel-p1

30 BHP Cast Iron Barrel Blog

The following pages trace the steps to achieve a 30+ BHP Italian barreled Lambretta engine and the hiccups along the way.

Page 1.

The barrel started life as an Italian GP 200 some time between 1969 and 1971, I purchased the barrel from Jason at Classically Italian in Birmingham who is now with Gran Sport, some time during the early 1990's. The barrel was at this time totally standard so it was a good candidate for tuning purposes.
Being from the Birmingham area I remembered a Lambretta that Stuart Owen had owned back in the 80's, I remembered this Lambretta was fast for its time. I asked Stuart if he still had the barrel and as I had never done any porting work at this time I asked him if he could copy the porting from his old barrel to the barrel I had purchased.

So the story begins....

The barrel performed well for many years as a stage 4 225 and ended up at 70.6 bore after a few re-bores.The one problem I always did have with it was cracks on the piston inlet side skirt, one time the skirt broke away level with the gudgeon pin while I was overtaking a car and exited out of the crankcase behind the crank webs, this left a huge hole in the casing just under the bump stop. Every winter following this I changed the Asso piston as a mater of course, seeing the piston as a consumable part. Doing this resulted in the engine being very reliable and in fact becoming a bit boring.

Sprinting at Santa Pod
While it was a stage 4 225 I did a bit of sprinting on it and achieved a best time of 17.03 seconds at Elvington some time around 2001. At this time the gearing was Italian GP 200 with 19 x 47 sprockets giving a final drive of 4.95, Exhaust was a JL KRP2 variant, Amal 30mm Carburetor and static Indian electronic ignition set at 18 degrees. The Lambretta the engine was fitted to was an Italian 125 DL which I bought the day it was imported into the UK also in the early 1990's. The paint work was done by myself using a small compressor with the number 5 added to the panels a few years later. The paint work shown in

these photos was the second colour I had painted it since owning the scooter. Originally the GP was for my wife who wanted it purple!

IoW on the green 2000 or 2001

Then in 2002 the GP was painted again by Jason Frost at Absolutely Scooters in Sheffield. For another 5 or 6 years the engine continued to be reliable, getting me to many rallies here and there. However by 2007 I was getting bored with just riding it so I decided to change the engine spec using the same barrel. I decided to do the tune myself so for a few months I gathered as much information about two stoke tuning as I could find and bought the tools to do the job.

The list of tools needed was something like this:

The list of components needed were:

  • 60 Or 62mm Crank With 115 Or 116 Con rod
  • Head Profiled To Match The Piston Crown
  • Better Clutch
  • Longer Gearing
  • New Carburetor
  • New Exhaust
Then All I needed to do was port the barrel and have the re-bore to 71mm

I Always wanted to have a longer stroke on the engine in the hope it would create more torque due to me always traveling two up with stupid amounts of luggage so I opted to base the tune around the H2 240 tune which was popular with the scooter racers before the invent of the TS1.
I chose the port timings I wanted to aim for from a two stroke tuning book by Graham Bell, I was aiming for between 130 - 135 degrees Transfer, 182 - 186 degrees Exhaust and 155 to 160 degrees Inlet. One thing that was annoying was having to use the complicated mathematical formulas to work out the port position I needed in the bore using a calculator so I decided to create an on-line calculator where I could just enter different port heights and it would give me the durations, you can find the calculators here
When I started playing with the on-line calculator I realised that the info given in the Webster Lambretta Tuning manual couldn't be correct because the durations and port heights given didn't correspond to each other. This made my mind up to just use the info given in the motorbike tuning manuals rather than any scooter related info thats is widely taken as gospel in the scootering fraternity.

Next page, let the hacking and slashing begin!


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