GP200 kitted? And what exhaust?

[DamionHoward.]

Hi, I’ve been away from Lambrettas for the last 10 years or so but just recently got another one. This is a bit of a weird one so bear with me please. The lad I bought it off had no knowledge whatsoever about the scooter (Indian GP200) all he knew was it had a 200 motor with a 28mm dellorto and a 42mm clubman, the scooter is rapid and will sit happily at 65-70 all day (recorded on GPS) my question are without stripping it all apart which I don’t want to do as it runs really well is there anyway of looking and seeing what has been done to it and would an expansion be a better choice than a clubman as it sometimes feels like it needs an extra gear- topping out but feels like there’s loads more to give. Any and all advice is welcome. Thank you!!

[citydaz]

Hi there, what exactly is it that you want the scooter to do?
Not a funny question, but a steady 65 - 70 mph sounds like good performance to me!
you may be opening a can of worms if you take a peek inside.
I would suggest leaving it a while and enjoy what you have!

[Scooterslag]

Hi there, what exactly is it that you want the scooter to do?
Not a funny question, but a steady 65 - 70 mph sounds like good performance to me!
you may be opening a can of worms if you take a peek inside.
I would suggest leaving it a while and enjoy what you have!

+1

[DamionHoward.]

Hi there, what exactly is it that you want the scooter to do?
Not a funny question, but a steady 65 - 70 mph sounds like good performance to me!
you may be opening a can of worms if you take a peek inside.
I would suggest leaving it a while and enjoy what you have!

I’m not really wanting it to do much more than it already does it’s more that it sounds like it’s hitting its limit and was wondering if an expansion would help it sound a little less like it’s screaming its head off.
I’m not really wanting to strip it down as it’s very reliable and starts first kick it’s more just curiosity about what’s inside it more than anything.

[gaz_powell]

I would keep that set up .... Unless you know what the top end and gearing is you could run into problems with a bad expansion choice.

Me being me, i would have to strip that to check it all with it being unknown.

Is the cylinder cast iron or Ali?

If you are able its a days work; side casing off and top off end check.
Fresh G/B oil, maybe rings... Then you have some confidence.

[Warkton Tornado No.1]

The likelihood is that an expansion chamber may increase performance, but on what basis would you select one? There are so many available that without an analysis of the top end, the best choice would be difficult to make. In any case, the increase in performance may be marginal:, but I couldn’t just ‘bolt on’ an item designed to optimise performance without matching the manifold to the cylinder via a proper, solid copper exhaust.

Sorry, but there’s only one way to do the job right, & that will involve the top end being dismantled for a complete analysis of squish, compression ratio, port timings, ignition timing etc, etc.

So, until that time arrives, just enjoy riding it

[LambrettaMarky]

I'm new to all this completely, & have a SIL GP200 that was essentially unused since a standard rebuild a few years back.

Originally it had the 22mm Jetex and a Rayspeed clubman exhaust with iron barrel & I think standard bore, piston etc. Timing is electronic though so that helps. in the bog stock trim I was lucky if it got to 50 and it didn't want to rev at all.

I checked the timing which was @ ~21degrees BTDC and have set that now to 17degrees BTDC & this helped massively. I also changed the carb' to a Scootopia (DelOrto) 22mm & again big improvement. With this set up I can get >60mph at a a push and sit comfortably @ 55+ depending on wind & hills of course.

If you are comfortably getting 65 - 70 mph I'd leave it well alone, but do a plug check to just confirm what the fuelling is like.

I would suggest a reverse pull front brake kit too.

[Warkton Tornado No.1]

Just to add my twopenny worth & as your latest, good advice has touched upon the subject, there is no definitive fixed timing, other than, from what we know about modern fuels & two stroke engine optimisation, a retarded ignition from OEM is a necessity. However, unless somebody can tell me otherwise, the amount to retard by is by no means cast in stone.

My belief is that if an engine is to remain safe yet provide a good performance, there are factors not often taken into consideration.

Nowadays, with two stroke engines in general, it is accepted that HPC (High Primary Compression) is not conducive to increasing power, though it will often increase torque. Great if all the riding is squirting the bike out of corners, but give the bike ‘it’s legs’ & it can start to hit a brick wall, especially when the exhaust ‘bleed’ is only, say, 19 mm. Traditionally the OEM box exhausts utilised such a restrictive tailpipe to function as a noise reduction device working in conjunction with the inbuilt wadding. That’s why the performance box exhausts we see currently have had to incorporate additional silencers because they will have a more sensible bleed of 25 mm.

I would suggest that there is a tendency to over-retard a fixed ignition, based upon not only the theory but experience. If the exhaust has an adequate bleed size & the best fuel (super unleaded) utilised, then I have found that for even a mildly ported cylinder, 19 DBTDC is a reasonable starting point & makes for a better bottom end in the performance. I’ve spoken of this previously, so my apologies, but WT No. 2 built a bike using all the principles based upon his only experiences which was in the 70’s/early 80’s. Consequently, when I checked the timing of the very mildly tweaked 200 with a PWK & expansion chamber, I was quite shocked, but had to say the performance was quite ‘sparkling’ compared to other ‘professionally-built’ engines I’ve been asked to try. Despite my warnings to him, he was adamant that ‘it would be alright’ & to be fair, it was while he owned that machine*

Undoubtedly the ‘J’ weight flywheel fitted to a GP boss contributed to the pep of the engine &, of course, that in itself aids acceleration/deceleration & reduces engine stress & load.

What I’m trying to say is that retarding a fixed ignition system is not an exact science. Whilst I personally apply the rule & recomend it, sometimes ‘less is more’

* for completeness of the tale, the other thing WT No. 2 was warned about was his use of a standard SIL crankshaft. The next owner of his perky machine experienced crankshaft failure…..

[bookertmgs1]

Quit while you are ahead.

If it will sit at those speeds then leave it alone until it doesn't. What benefit would be achived by changing anything - most rides / trips arent going any faster than that.

Appreciate that there is an overwhelming urge to tinker but unless you are doing all your own spannering then I'd leave it. At somepoint you'll have to strip it down and you can find out then.

Until that point - just enjoy having a reliable well performing scooter

[LambrettaMarky]

My flywheel weighs 2.66KG.. Is that about right?

[LambrettaMarky]

Flywheel by KTM Marky, on Flickr

[Rich Oswald]

Hi there, what exactly is it that you want the scooter to do?
Not a funny question, but a steady 65 - 70 mph sounds like good performance to me!
you may be opening a can of worms if you take a peek inside.
I would suggest leaving it a while and enjoy what you have!

+1

+2

[DamionHoward.]

Thanks for all the advice on this, I’ve had it out for a good blast today and it honestly runs like a dream so I’m going to just keep riding and enjoying it until something goes wrong and it needs a rebuild (a long time to come hopefully!) it’s a cast cylinder so it’s not got an ally kit on. It’s just annoying when you know it’s had something done but you can’t pinpoint exactly what’s been done.
Again thanks for all the help and advice!