Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board 1970 thunderbolt help

Hi to everyone

I purchased a 70 thunderbolt. The previous owner installed a device to eliminate the battery. After I purchased the bike I removed that devive { capacitor}
and installed a battery. new carb from Lowbrow customs.new plugs and new 6 volt coils. cleaned the points slightly with 400 grit sandpaper. the gap looks to be .38mm.The po had a 2 wire ignition switch, there is a tympanum. After I purchased the bike I could not get it started. bike has great compression and the po said the engine was rebuilt. After I installed all the new items I still cannot get the bike started. I have a new ignition switch I plan to install. I read tht you can bypass everything by running a wire from the neg side of the battery directly to the coils just to get it started. how do you do that.
ps there were no fuses but I installed one from batt positive to ground. there were also no wiring on the ammeter. It looks like the po has a minimium wiring custom on this bike. He even has a toggle switch to turn on lights. I assume since the capacitoe would not be bogged down. how can I get this bike started

Thanks for everyones help

If you are running points, you need 12v coils. If you have electronic ignition, you use 6 volt coils. You could upgrade to a Pazon or Boyer electronic ignition and keep the coils you have. If you run one of those you can run a jumper wire with a switch and fuse from battery negative to the white input wire on the ei box to get you started as a temporary fix til you get the wiring sorted.

If the bike still has breaker point ignition, yes, you can run a wire directly from the battery (-) to either one of your coils. Note, if the engine starts, you will have to stall it to stop. Or, you could put an inline fuse or a switch in that wire.

Ok

Ill switch back to the 12 volt coils. I do have a Boyer ignition system new in the box I will install once I get the bike sorted.

so to recap, to get the bike started I will run a wire from batt negative to coils. where on the coils, neg or pos?

Thank you for all your help

If the 6v coils are already mounted, why not just fit the Boyer? The chances of you starting and running the bike are probably higher providing your battery is good and you can always connect the Boyer directly to the battery initially if you feel you have other electrical gremlins. Trying to time the ignition will also be a pinch with the Boyer and more time consuming with the points.

I'd rather put the 12 volt coils back on and make sure the bike starts, resolve any timing issues, ensure the new carb is working properly. Resolve the wiring problems, i.e. New ignition switch and ammeter wiring Before I install the Boyer. If I put the Boyer on now and the bike doesn't start then I've just created more of an unknown. So, to recap I want to run a wire from the neg side of the Batt to any coil. Where does the wire from the Batt neg go, to pos or neg on the coil?

Thanks for all help. It's appreciated.

Look at the coils, see the white wire, thats the hot feed from the ignition switch, connect the batt neg to the white wire terminal to hot wire.
The coil terminal should be marked negative.
Trying to revive old points, first clean points with a fine abrasive paper drawn through, next replace capacitors, test for spark at plugs by flickin open points.
To check timing, remove the primary cover strobe access plate at the front of the cover, put a fag / rizla paper between points, rotate motor till strobe pointer lines up with rotor mark, advance the points a/r mech/ ( twist cam opposite to normal wheel rotation), the fag paper should just pull free.

For the carbs you need a #78 drill, 0.016" diameter, use this to clean the pilot jets, reset pilot air screws about 1 full turn out from closed, this should be in the ball park to get the motor started.

Something to note regarding timing, the points cam is mounted on the idler pinion, this rotates in the opposite direction to the motor/ wheels.
Something else to note, trying to clean the carbs without a #78 drill is a senseless waste of human effort.
And another thing, capacitors / condensers have a shelf life, finite life span, if the motor runs but the points give big orange sparks, the capacitors are FUBAR.

the negitive side is the switched side . ( any and all switches are on the negative side )
If the switch is defective you jump the switch and part of the harness wire .
( but it's always negative to negative ) for a positive ground bike

a wire is run from the negative battery terminal... to either coil negative terminal .
This is how you hotwire and steal your own bike

( this only works if the two coils already have a jumper wire between them
... which they will , if the bike is still somewhat wired correctly )

before you do the jumper ,
check for battery voltage at both coil negative terminals . ( the proposed jump point )
there should be a mess of white wires around the coils , and more than one wire to each negative terminal .
If you have full battery power here ... when the key switch is operated ... you don't need a jumper .
( if you have no or only partial battery voltage here ... the jumper can help )

If you don't have full power at either coil when the key is Switched ... a jumper will add full power .

For safety reasons the jumper really should have a toggle switch and a fuse
The whole thing can be made out of 2 insulated alligator clips , a small length of wire ... and a 15~20 amp fuse .
place the fuse as close as is practical to one end ... and use this end at the neg batt term.

power at the coils for this year is split and operates more than the coils .
So adding (jumping ) power here may immediately blow the fuse
... at which point all of the white wires at the coils must come off
and only certain ones added back on .

Thank you all for your help and advice, it is very much appreciated.

CBS , sponsors here have an excellent explanation of the Lucas 6 CA points , it should help, just remeber the A65 cam rotation is backwards from the Triumph shown in the images.https://www.classicbritishspares.com/blogs/news/Lucas-6ca-anatomy

The wire would go from battery (-) to negative on either of the coils. If the coils are not marked, it would be the terminal that the white wire is connected to. You should see a jumper between the negative terminals of both coils. You can disconnect the white wire coming from the harness from the coil, in order to free up a blade terminal.

Have you actually looked to see if it is sparking or not?