Scooterotica

So it should. There's definitely something wrong somewhere.

Like I said, I'm new to Lambrettas so hopefully I haven't made some school boy error during the rebuild.

I've written directly to Gori asking for ball park jetting figures, but am waiting on a reply. They were helpful before I bought the kit, so hopefully they give me some after sales advice.

If I can't get anywhere then maybe I try a PHBL?

holty wrote: ↑Wed May 02, 2018 9:27 am

HxPaul wrote: ↑Wed May 02, 2018 9:00 am I set and strobe both of my scooters at 17degrees BTDC,in my opinion 24 is to advanced with the petrol we use nowadays.

i think he said he is using casatronic ignition, so has advance and retard i think, otherwise i would agree with you 17 degees is a safe figure on a fixed ignition.

Oops!Thats the second time I've been caught out by that.(Memo to my self.Must read all of the post).

Just been out and reset the ignition timing to 23* and swapped the 5899-2 for a leaner 5899-1. This seemed to have some effect as it now runs okay with a 118 main (still a slight judder).

Andy from Gori also replied and said not to worry about the settings as long as the plug colour is good. He said he was a bit surprised the BGM pipe doesn't need a bigger main but not to stress as long as the plug readings are fine. He also pointed out that jetting tends to vary from country to country (it's about 5*c here in Helsinki and 30m ASL).

On that advice, I'll leave the ignition timing at 23* and just work on finding the best jet compromise. Will then ride cautiously and do plug chops. Thanks for your suggestions and advice.

Will update later when I've got it running right and tell the set up, just in case it helps someone else in the future.

scandical wrote: ↑Wed May 02, 2018 3:35 pm Interesting to hear that you have the same kit with a stock pipe Grumpy, and yet are still running a bigger main jet. What atomiser do you have fitted?

To be honest, apart from shooting up and down my road to feel how each jet combination works, I haven't done any driving, so the plug colour probably isn't a good reflection yet. I need to ride it a bit more with the 102 main, 50 idle set up before the plug can be read.

I have a BGM Clubman V4 fitted and I had assumed it would also push the main jet up a couple of sizes.

I have the 5899-2 in that carb. It's stock GP 200 jetting across the board.

Now this set up is not as crisp feeling as my RT with a 24 PHBH but it does pull smoothly to WOT and behaves like I'd expect it to. Feels like a fast stock 200.

I think that 50 idle jet is causing you the jetting problem. You're on the right track by leaning out the atomizer and increasing the main.

Did you check your squish (and ring gap) when building the engine........too big a squish may result in similar problems.

I haven't check the squish yet.

Thanks for the suggestion. I'm looking for about 1.5mm, right?

A short update; having bought numerous jets and tested different combinations, I still find that my Gori 200 runs best with a 50 idle jet and a tiny 100 main - when running the BGM filter.

When I remove the air filter completely, it runs smooth and pulls well. Even with no filter but running through the air box, it splutters and is craving for more air. My Italian friend always runs his GP without a filter and suggested I up jet and do the same.

Using a 3D printer I've designed a compact filter that can fit directly onto the carb, underneath the panel. Not the original look I wanted, but needs must. Hopefully this will allow the engine to breath whilst offering some basic protection against grit and other crap.

Watch out that you're not over weakening the main (full throttle) to resolve / restrict the 200 atomiser delivering too much too soon at 1/2-3/4 throttle! If you do then you have a very good chance of it then riding through the previously rich zone and then running VERY weak upwards of 3/4.

This is a well known issue when trying to run standard carbs on tuned motors and is why you will find many (me included) running a weaker atomiser and correctly sized main jet. A typical combination would be a Dellorto (bin the others!) GP150 atomiser (5899-4) and a 120-135 main jet. Obviously, this will be influenced by the combination of cc, air filter and airbox specification (pre III, SIII, GP, modified GP [baffle and or drilled], BGM), spec of porting and pipe.

I have also known one iron 175 that ran very well with LI150 atomiser (5899-1) and something like a 115-118 main jet in 22 Jetex and with clubman.

IMO you're going the wrong way by introducing a restriction my fitting small main... and putting yourself and motor at risk.

Best of luck with it.

Adam