SIL GP 200 - 'Stage 4' Barrel Tuning

[LambrettaMarky]

I plan before going for a complete kit, to look at 'carefully' porting my own barrel & checking/adjusting squish, spark plug length etc. Reading Sticky's kit book, there is plenty of opportunity to better the standard SIL barrel/head/piston set up & it doesn't look overly tricky.

I'll get myself a set of good quality burrs & already have a high speed air drill that I think will be OK to get into the ports with.

I have a few questions if anyone can help me with please & I already have the JL3 pipe & PHBH30mm carb':

• Is this the best piston to use & if necessary I can hone the barrel & go up a size or two: https://www.lambretta.co.uk/product_inf ... ts_id=3283
• What is the optimum squish to set the barrel height to?
• Is there a drawing somewhere with port dimensions internal & external that I can use as a guide?
• Can I get the top end off if I raise the scooted on the stand and remove the engine mount to drop the motor pivoting forward?
• Any words of wisdom or tips in general?

I am quite happy with the progress so far from what I started with, so maybe a mild tune and port clean up will give me just another few mph. I'll upgrade the ignition system with a Vape unit too while I'm at it.

Thanks folks.

[Adam_Winstone]

And so it begins.... (the Lambretta tuning journey).

From my own experience, yes, the World is your oyster, with lots of potential for more power but not without risk of compromising reliability and swapping a wide RPM range of torque for more HP at higher revs. Typically, you can easily make higher BHP but pushing power higher up the rev range may require a lower top gear ratio to stay in the powerband, ofter resulting in a similar top speed.

If you want to see a very well presented tuning feature for your current SIL 200, get hold of Darrell Taylor's 'Bang for Buck' series that was published a few years ago in Scootering magazine. This will give you all of the detail that you're looking for.

Adam

[Adam_Winstone]

... but are you sure that you don't want to keep it as it is for a season, for you to better understand the capabilities of your starting point, enjoy the reliability that your current arrangement should return, get to know the demands of the bike, etc?

PS - This comes from someone who has been down this route and still struggles to leave a top end alone (lol). I mention this as I have seen so many people write off perfectly good / fast top ends by following published advice on widening exhaust ports and breaking rings. Also note that much of today's Lambretta tuning advice (and spec of kits) has been developed hand in hand with the production of 5-speed gearboxes, where narrow powerbands can span the loss of power across a wider RPM range. Many modern kits and tuning advice falls pretty flat with factory 4-speed boxes.

You really are at the thin end of the wedge.

[LambrettaMarky]

Good points well made Adam, thank you.

I am collating ideas & information at the moment, but you are absolutely right in that now is not the right time to disassemble a perfectly good running scooter. I'm not yet attending rallies regularly or putting many mile on the scooter at all really, but I hope that will change now that at least I do have some mild performance over the initial starting point.

If it's a quick win over a weekend's work in the garage then I'm happy to do that sooner rather than later.

[Adam_Winstone]

Do get hold of a copy of Darrell Taylor's 'Bang for Buck' series though as it has all of the info that you are looking for.

Even then, read it in full and keep an open mind to other opinions. Not everything that increases power will do so in a manner that suits all rider preferences.

Easy wins are few and far between (there are some though) and you'll typically find that there are 'trade offs', rather than outright wins.

Enjoy the journey and learning process. I still love it and every day is a school day

[LambrettaMarky]

Do get hold of a copy of Darrell Taylor's 'Bang for Buck' series though as it has all of the info that you are looking for.

Even then, read it in full and keep an open mind to other opinions. Not everything that increases power will do so in a manner that suits all rider preferences.

Easy wins are few and far between (there are some though) and you'll typically find that there are 'trade offs', rather than outright wins.

Enjoy the journey and learning process. I still love it and every day is a school day

Thanks & Yes, I'll have a read first.