Li150 S3 ignition timing

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Freoway
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Fri Mar 05, 2021 1:21 am

Hi. I understand that my Lambo should run at around 19 or 23deg BTDC for ignition timing, partly depending on whether fuel is unleaded or not. My Lambretta has never been running since I've owned it, but I've spent some time rebuilding the motor, carb, etc. It will fire and run for a few seconds when I kick it over, but it will not run for longer. I thought it may be fuel problems, but then I checked my timing and it's only at about 10BTDC. Is that far enough away from it's right timing that it would cause the engine not to run?

Warkton Tornado No.1
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Fri Mar 05, 2021 11:02 pm

Like most of us continuously involved with Lambrettas from the days of high octane leaded fuel, I have delved into the specific reasoning for retarding ignitions. The most common need is because of the reduction of anti-knock properties that the lead gave to petrol prior to it's abolition. The other requirement for retardation is associated with the efficiancy of the burn as the revs rise, hence active variable retarding ignition systems.

There is no definitive amount by which a fixed ignition should be retarded from the OEM standards of years ago, but some would advocate that more is better. I'm cynical of that & normally set up the static ignitions only retarded a couple of degrees @ 19 DBTDC. However, I am also extremely particular about compression ratios & squish.

Unless you know what the factors just mentioned are, you may as well follow the herd & set it @ 17 DBTDC. Whilst that is safe, it is unlikely to endow the engine with a sparkling, responsive engine.

Only 10 DBTDC is bad news & there could be the risk of the engine even running backwards. I am not joking.

Better to set it & 19 DBTDC & do lots of plug chops. How to do so properly is a subject in itself.

A mate of mine recently built his Lambretta to the old ways. Ignition was 21 DBTDC. Surprisingly, it ran superbly & no signs of pinking. He did use Super Unleaded though.....

Freoway
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Sat Mar 06, 2021 3:15 am

Thanks Warkton Tornado No.1. Much appreciated. On classic cars I usually set it to the prescribed timing and then make minor adjustments from there, based on vacuum and driving tests, etc. I'm aware of all the factors you mention, just no experience on 2 strokes. I'm using as 12V timing light to measure the timing, which works well. Cheers,

Warkton Tornado No.1
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Sat Mar 06, 2021 4:01 pm

You're welcome.

Two strokes are wonderful engines, though few people realise their potential. They are the most efficient 'widely' (or commercially) manufactured engines in the world, dependent upon your perspective. Ships engines use supercharged, diesel two stroke engines.

As for older other vehicles, I bought one once that came to me retarded too much, so I gradually advanced it until it started to just pink then knocked it back a tad. As a consequence, despite cross plies on the front which meant if you farted, you'd change direction, I got her up to 85 mph.

How I now regret selling that Devon Conversions 1500 cc VW split screen camper.....

Warkton Tornado No.1
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Sat Mar 06, 2021 4:36 pm

Forgot to mention in case you are unaware.....

Points based ignitions work better with non suppressed caps & plugs.

In my personal experience, I've had a far greater percentage of duff NGK plugs than any other brand. More so with the standard products than the more expensive race variety. As I have dozens of them, NGK ought to be my automatic choice, but, unfortunately, that is not so.

Champion plugs & caps are now my first choice, just like Ray Kemp used to advocate & to emphasise that fact, Rayspeed sell a good range..

When I can spot a fine wire Champion plug on eBay @ sensible money I bid on it to use with same brand rubberised (Oooer!)unsuppressed plug caps. That said, N3, N4 etc are good enough, but my tuned Rapido (71 x 61) 34 mm PWK tempts me to hammer it from time to time when tw@ts think they can cut me up & get away......

You can also spin up your engine with plug out using a good electric drill (not impact type!) fitted with a 17 mm AF socket & your 12v powered strobe to set timing. Saves a lot of legwork. Ha!

Freoway
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Sun Mar 07, 2021 7:37 am

Thanks for all your advice. I have a friend whose profession is to restore VW's, including many splitties/splitscreens, beetles, Kharman Ghia's etc. Never short on business! I've always had a good run with NGK plugs (mainly in old 1950's, 60's V8s). I use the same technique for timing - advance until it pings then back it off a bit. Alternatively, set it to where it's meant to be, then make minor adjustments to maximise manifold vacuum. Funny about the VW campers, they're so valuable now and there are so many more of them on the road. People have having complete rust buckets brought back to life for big money. As for setting the timing, I use the approach you mentioned above, but found that I'd keep unscrewing the nut (since it has a reverse thread). So I pulled the plug out and earthed it, which worked fine.

Warkton Tornado No.1
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Sun Mar 07, 2021 9:51 pm

Thanks for the response.

Besides the split, I had a Variant Automatic (44 BHP with a power/torque sapping slush box), a 'normal' KG & a 'razor edge' KG.

I've still got loads of bits such as alternators, bright trim, door handles etc.

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