Timing

[Danbretta]

I know this has been asked numerous times and the more I delve into the web and forum to forum the answers slightly differ. I have a big standard Li150S still running 6volt (that I'm happy to do so). My question is, what BTDC should I be going for these days, I know the original was 23° and at some stage due to the quality of fuel was recommended to go to 21°. I see a few recommendations online with 19° being the new standard.
I just want some confirmation as to whether this was aimed at tuned engines or does it cover standard too.
I found having it set nearer to 23° the bike was so easy to start. It wasnt until I retarded the ignition that it started taking longer to kick over. So if I was to advance the timing back would it become detrimental to the piston and firing or should I persist with getting it running better retarded.
I use shell V power over the standard at the pumps on the assumption its the better fuel with a higher RON but with the extra additives and detergents they advertise would this work against the oil to fuel mix, would the detergents really affect the oil and lubrication in the cylinder or is tgus another online myth?

Thanks in advance should anyone be able to give me some guidance.

[Adam_Winstone]

Bit of a can of worms this topic as people often respond to fight their corner, however, if you want a well explained review of the relationship of ignition timing for Lambretta today, touching on standard and tuned requirements, see Dan Clare's (Scootering Editor) video that he has posted on social media. This vid will gives you some recommendations but will also explain why.

Personally, I'd not set any motor to mote than 19 degrees btdc but the vid does give you an understanding as to why some motors may cope with more advance.

[Danbretta]

Thanks Adam, I'll take a look

[Warkton Tornado No.1]

Good advice from Adam, though I was unaware of the video. I will watch that too, soon....

It is an interesting question you're raised, because there are two main reasons for retarding ignition:

When an engine's power efficiency has been raised, the carburettor delivers it's charge in the form of a much finer 'mist' of the mixture of petroil & air. A finer mist has a larger surface area comprising, therefore, more oxygen. More oxygen needs less advance, therefore the logic to a retarding ignition on a two stroke.

The other reason is the fuel that we use which no longer has lead in it. When lead was no longer available in fuel, in particular, older four strokes required retarding to cope.


Personally, I retard ignitions on any engines that I build, but that is principally because they are invariably tuned.

However, an old mate still living in a time warp, re-acquainted himself with Lambretta, by building from scratch based upon his knowledge of points ignition. It had negligible tuning, just a matched manifold & filtered 34 mm PWK with an expansion.
It ran superbly well. He used super unleaded with 21 BTDC.

I personally opt for Tesco Ultima in my scoots but my 240,000 diesel runs on Shell V power & I can tell how smoother it is as a consequence.

If I were you, I'd just keep doing as you are/were @ 23 BTDC but keep an eye on things. The spark plug is a good indicator. BTW.....points ignitions are better for a non suppressed cap.

Ideally, the top end would benefit from a good check over to judge combustion area.

[Danbretta]

Thanks for your reply, it's much appreciated. This has been my first engine build and theres always doubt everything is set up and working right inside the engine. Theres a part of me fearing a bearing failure or a holed piston..

At the moment it's set up at 21° I'll see how I get on with it and monitor the top end as you suggest. If I need to retard further I'll have to open up the stator holes as I'm on the limit now I cant rotate the plate much further

Here's the link if anyone is interested to view Dan's youtube video.

https://youtu.be/rWHoAb0xPMk

Interesting viewing.