bsa lightning

[marty 31]

my 1969 lightning has been professionally rebuilt and now on the road, it starts fine, and runs fine, but when its fully hot, stopped then re started its a pig to get going, it has brand new consentric  carbs, the correct jets set to the makers settings, but the plugs always look sooty and damp, one thing that has been pointed out is there is no heat spacers between the carbs and manifold, just a gasket, could this be the problem? or would dropping the needle in the carbs one (last) notch help? thanks in advance for any advice and help.

[L.A.B.]

one thing that has been pointed out is there is no heat spacers between the carbs and manifold, just a gasket, could this be the problem?

Yes, it could be, or at least the lack of heat spacers won't be helping matters so I suggest you fit them because they should be there (70-7821 according to the parts list).

https://www.draganfly.co.uk/index.php/bsa/bsa/a50-a-a65/1969/category/313-69-cylinder-barrel-valves

or would dropping the needle in the carbs one (last) notch help?

The Lightning needles should be at the No.1 weakest position (clip in the top groove) according to the '69 - '70 factory manual.

[marty 31]

my needle settings are set second last setting(2nd weakest) so I will try dropping them, also look at my parts list and try and get spacers, as the carbs seem very hot, after fully warmed up, thanks for the advice

[L.A.B.]

also look at my parts list and try and get spacers,

There should also be an O-ring (622/101) on the carb side of each spacer.
https://www.draganfly.co.uk/index.php/bsa/bsa/a50-a-a65/concentric-carburetter

[marty 31]

after looking at the parts list, the heat spacer looks more like a thick gasket, would that be right? or as I was expecting would it be a proper spacer? ie maybe 10-15mm thick or so?

[L.A.B.]

after looking at the parts list, the heat spacer looks more like a thick gasket, would that be right?

I'm not sure but if they were then the originals could have been an asbestos composite material which you wouldn't necessarily want and probably aren't available now.

or as I was expecting would it be a proper spacer? ie maybe 10-15mm thick or so?

The thicker the better but I don't think the studs would be long enough for ones 10-15mm thick and the 70-7821 spacers available are thinner.

[TGR90B]

It depends on the insulation properties of the material. I think a material called tufnol (?) is effective at about 3mm thick. It's only to stop conducted heat between the flanges and minimise fuel evaporation.

[iansoady]

Hitchcocks among others stock Tufnol spacers.

[marty 31]

think I have the 3mm ones from a srm gasket set, good job for sunday, tank off, fiddly carbs adjusted, and gaskets fitted, then if dry go go go, thanks for the much appreciated advice and I will update the outcome

[33d6]

You describe the classic symptoms of a dying ignition system, that is, starts well when cold but a pig when hot. This is something that is nigh impossible to pick up beforehand and only starts to show after a good run when the engine is well and truly hot. Your professional rebuilder would have had little chance of picking it up given the limited miles they are able to put on a bike before it is returned to it's owner.

By all means do everything that has been suggested above. They will all help ease the burden on the ignition a little and are sensible suggestions anyway but they won't effect a permanent cure. The approaching cooler weather will also help as the engine will take longer to get really hot. The real test will come on the first hot day of next summer and you do your first long ride of the season.

If you can find an ancient old time mechanic ask him how often are carburettor problems cured by sorting out the ignition. He will have entertaining stories to tell you.

Best of luck with the beastie.

[iansoady]

I'd agree if it was a magneto setup but would be less sure it was ignition on a coil job, especially as you effectively have 2 completely separate systems for the 2 cylinders.

Having said that, new HT leads and plug caps are cheap enough and always worth changing. I would not suspect capacitors as they usually cause bad starting in all conditions.

The above assumes it still has the standard points / coil arrangement.

[marty 31]

it has been changed to electronic ignition (before I bought it) and the engine hadn't been run by the engine builder, I set it up with all settings by the book, my manual stated the carb needle setting was second from the top (2nd weakest ) but is has been pointed out that another book states top notch so as the plugs always seem sooty and damp it might be worth a try, thanks for any advice

[33d6]

Not so Ian, heat failure occurs in all variety of spark ignition systems regardless of how the spark is generated. In fact the last time I experienced it was on a Triumph TR7 fitted with an aftermarket electronic system displaying exactly the symptoms Marty 31 complains of.

Electronic ignition is an improvement but it is subject to the same woes as all the previous systems-just not as often.

Whatever the case, I'm sure Marty 31 will learn a lot sorting it out.

[iansoady]

True, but with 2 coils how likely is it that both will have the same problem?

But I wouldn't rule it out.

[33d6]

I just hope we finally get to hear the end of the story. With so many of these queries they trail away to nothing. We're left guessing.

A happy ending always goes down well.