classic motorcycle forum

I have measured the bore at 68.5mm and the piston from its very bottom of stroke to very top of stroke travels 75mm. According to the online calculator I used it is a 276cc ? Have i got this right ?

Yes.

With the angled top on the piston does this have any bearing.

No.

its blue box, the exact kit you have kindly shown, the exact same coils etc

You say "coils"? I assume you mean the single dual output coil as shown in the picture and not two separate single output coils?

If you do actually mean two separate single coils then how are they wired?

the modern type regulator/rectifier dosent seem to have a makers name on it, these modern add ons are all a good idea but bypass the makers manual,

Does charging system appear to be working normally? Have you checked the voltage (both battery and charging)?

another thought is could the earth on the coils be maybe not good enough? as they are not earthed direct from the fixing because they had to be cable tied to the frame and couldn't be fixed to it,

According to the Micro-Power instructions (below), only the (+) terminal (of the dual coil) has to be earthed (the coil body is plastic) and only if positive earth.

http://www.boyerbransden.com/pdf/KIT00281.pdf

the bike runs on electronic ignition and is timed bang on, so next try is going to be new 12 volt coils, does anybody agree and advise this?

As it has "electronic ignition" (which make/type?) then it's more likely to require two 6V coils (connected in series or one 12V dual coil) for best performance.

or am I just wasting just more hard earned money?

Possibly.

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.

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.

Judging by the condition of that wiring the best thing to do would be to rip it out and replace it.

or this even , If you are not in a hurry
https://www.ebay.co.uk/itm/KBPC5010-1000-Volt-Bridge-Rectifier-50-Amp-50A-Metal-Case-1000V-Diode-Bridge/291862837146?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20131017132637%26meid%3D5ca3b54b4b66480bb0cfb182320b7463%26pid%3D100033%26rk%3D3%26rkt%3D8%26sd%3D223116553410%26itm%3D291862837146&_trksid=p2045573.c100033.m2042

https://www.ebay.co.uk/itm/British-motorcycle-solid-state-rectifier/223116553410?hash=item33f2c86cc2:g:SGgAAOSwInxXOPCG

"I can buy in the KBPC 50-10 rectifier at 56 pence .I could start selling that type,however,they do not work in the same manner as the correct KBPC 35-04 that i supply.Sharp practice to be selling the wrong rectifiers as suitable on classic bikes."

Pics of old and new attached  but there are so many options for connections on the new one, and I just cant get my head around the directions of the diodes

As standard, your Tiger Cub's electrical system would be positive earth/ground.

That rectifier is not only a nine-diode type for a three-phase excited field (slip-ring) alternator as it appears to be a rectifier for a Lucas "ACR" alternator but it is almost certainly negative earth polarity. 

http://freerollguide.net/probably-fantastic-free-automotive-alternator-wiring-diagram-pictures/images-of-wiring-diagram-lucas-18-acr-alternator-wiring-diagram-image138-that-great/


https://www.ebay.ie/itm/REPLACEMENT-12-VOLT-ALTERNATOR-RECTIFIER-LUCAS-ACR-LRA100-UBB109-83166-130643-/281815311556

A 4-diode rectifier like this is all that's required as it can be used for either positive or negative earth.
http://www.rexs-speedshop.com/Single-Phase-Bridge-Rectifier 

Or:
http://www.classicmotorcyclespares.com/index.php/default/electrical/charging-system/classic-bike-rectifiers-regulators-bsa-triumph-norton/rectifier-replica-lucas-positive-earth.html#Charging_System

The old selenium rectifier needs throwing in the bin, regardless.