Carbs have a few sections of operation over the throttle range.
You've established the the beginning , starting bit is fine.
Have you or did you - before fitting it - check that the inner needles and jets were correct to specification in the C15 book ?
Check them and come back

Ok thin spark.
This could well be the issue all along.
If it is a weak spark outside the engine , even the meagre compression ratio of the C15 could well extinguish this spark when inside the engine .
Basically , blow it out and it won't run.

Was this test using just the ht lead against the engine or a spark plug pushed into the plug cap

What colour was the spark , strong blue crack

If it's a metal mushroom behind the cylinder barrel , then that's refered to as a distributor.
So follow the instructions , from memory 1/16" before tdc in the retarded position , don't touch bobweights.

Have you determined the 1/4" spark gap colour , blue or ?

Do you have the distributor ignition or the side points.
Reason I ask, the books I sent you were very clear,
Distributor timing was set retarded and sidepoints ignition set fully advanced.
What do you have ?

ideally , you should have a shade more really. my Son's C15 is quite easy to kick over TDC , but I have never actually measured the psi. i think the C15s were 7:1 CR

conversely, my SS80 is 8.5:1 and is significantly harder to get over TDC

do your tappets carefully , check the spark is a good blue crack (unscrew the HT cap) and lay the end of the ht lead on the head , jam it in the fins to give a good 1/4" gap to jump

As in an earlier reply, have you correctly positioned the engine to adjust the valves . It's quite precise.
And I have sent you both books with the procedure inside.
A decent , well adjusted set of points will spark a bike or car fine.
The c15s were lowish compressions anyway.
I use a gammatronic 6v kit on another bike.
And that works fine , from memory about 35 quid.
You're correct , get it running 1st on what you have , in the 60s and 70s I did thousands of miles reliably on points and condensers.

The valves are quite specific in the places where you asjust 1 valve after positioning the other valve carefully.

The earlier book for the distributor engine  I think indicated setting around 1/16" at the retarded.
Whereas , the other books indicated how to hold the advance retard unit fully advanced.

I have sent you instructions for a distributor timing and side points timing

If it was running a few months ago , was it running well or not very well.
Ok difficult to start , but did eventually

You mentioned sparking , what colour spark , must be strong blue crack
Preferably unscrew the plug cap from the lead and jam the ht lead between 2 head fins to give you 1/4" gap for the spark to jump.

Does the spark jump the gap and what colour

Can you borrow a compression gauge to see exactly what the compression is , valve clearances checked correct ?

What year is your c15 as it makes a difference

Has this bike ever run in your ownership?

Do you want the timing procedure in the manual

The c15 has 2 options on the switch
1 is normal on and this is where you should be running

2 is emergency starting , which is only used if your battery is flat ( you've left your lights on)


According to the manual , Emer can only be selected by depressing the key and turning clockwise.
(But I don't know , from which direction it is looking)

Just to explain advance and retard in terms of you looking at the points cam.

Determine the direction of rotation of your engine when kicking it over.
Anti clock or clockwise.??

If you wish to advance the timing then the points plate or distributor body need to be rotated in the opposite direction- ie against the direction of rotation.

Conversely , to retard the ignition the points plate of distributor needs to be rotated with the direction of rotation.

I've just taken a pic of my owner manual regarding starting.
I don't have any joy uploading stuff , if you can message me , I'll send to you

Ok 2.25mm btdc
The points should just opening (give or take) here with the advance retard unit held fully advanced.

Put it this way , it should at least start and run here

Quote from: scifi on 04 May, 2025, 08:36:42Just to be pedantic, you said...
Then

Just below this mark , file another mark at the distance the book says before tdc it should fire.
So, if it is 3/16" before tdc , put your lower mark 3/16" apart.

You would need to put the second mark -above- the first mark.   Making the length of wire 3/16 longer.

Also when kicking from TDC, try to extend your swing forwards, for the maximum kick rotation.

My apologies, the 2nd mark must be above the 1st mark , to ensure the points opening position is on the way upwards to tdc