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User avatar
By stinkwheel
#99244
I've taken the electrex electronic ignition off my 612 pre-unit bullet and re-fitted the points. Any time I've strobed it, it's been "glitchy" with regard to the fully advanced, it hits the fully advanced firing point normally but then wanders more than I'm comfortable with and I don't seem to be able to find a point where it's correct at fully retarded then hitting the correct fully advanced mark. I also went in past Hitchcocks for some other bits a while ago and they pulled faces when I said it had an electronic ignition.

Anyway, points on and it runs but it also looks like I have way too much advance on the auto-advance unit, there's 27 degrees of movement on it so if I set the fully advanced to 32 degrees, my idle is 5 degrees. Winding it back a touch to maybe 30 degrees to try to avoid pinking (it's running pretty high compression) puts the idle at 3 degrees BTDC. This makes it latchy to start then it "runs away" when it advances slightly and won't settle back down again. I can set it for a lovely clean start, idle and pick-up off the throttle but then it's too far advanced at full speed. I can't get a clean idle with less than 7 degrees at idle which puts fully advanced at 34 degrees, which is way too much.

It'll need new springs anyway to try to hold it in the retarded position for a bit longer (and they are the original springs which will be pretty weak) but I was wondering if there's a known way of adjusting the amount it advances? The answer is probably a new unit but they're getting thin on the ground unless you go to India. Also I think it would be good to try it with even less advance than the standard 22 degrees.

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User avatar
By Wheaters
#99247
I’m not familiar with the actual mechanism of these units but presumably, in addition to the springs, which control the rate of advance, there is a maximum advance stop. In the past I carried out a lot of work modifying Lucas distributors to adjust the advance curve for my very high compression 850cc, 4 cylinder Reliant engine. I used a blob of weld on the max advance stop post, then filed it back until I got the max advance I needed.

Is there a way of doing this on a Bullet?
User avatar
By Wheaters
#99248
OK, I found an exploded diagram in the parts list.

It looks like the advance weights have a curved slot on their front side and this engages over a fixed peg. The weights pivot around another peg and fly out against their springs with increasing rpm until the end of the slot touches the peg, preventing any further outward movement. That’s the point of maximum advance.

To limit the total advance you would need to reduce the length of the slot. Bear in mind that every degree of advance at the distributor equals two degrees at the crank.

You might be able to do this by jamming in something like a piece of solder, which could be picked out again if needed.
User avatar
By stinkwheel
#99250
Yes, that's how they work. Picture of advance weights here (I took it because these two were fitted to another bike I bought. The one on the right is Redditch made and the slot is narrower than the Indian one on the left. Which was causing issues with it sticking):
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I don't think my welding is good enough to be adding material to those slots. Looking at the pins, they seem to be push-fit. I have a spare base somewhere. I'm wondering if I'd be able to do something with the pin like making a marginally oversize one and filing the sides slightly oval so the weight slides on it but comes to a stop sooner. I'd probably only need to do one of them.
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#99251
34 degrees full advance is not too much, if you have pinking, the cylinder pressure on the compression stroke is too high, and / or your mixture is too weak at certain throttle openings. I overcame this on the 612 engine I built for 'Slo Poke' by retarding the Hitchcocks inlet cam by 1 tooth.
User avatar
By stinkwheel
#99255
Bullet Whisperer wrote:
Tue Dec 07, 2021 8:12 pm
34 degrees full advance is not too much, if you have pinking, the cylinder pressure on the compression stroke is too high, and / or your mixture is too weak at certain throttle openings. I overcame this on the 612 engine I built for 'Slo Poke' by retarding the Hitchcocks inlet cam by 1 tooth.
Good to know.

I've done the inlet cam thing. I think I'm just going to have to lower the compression to maybe halfway between where it is now (1x3mm plate, 2x base gaskets) and where it was before (2+3mm plates and 3x base gaskets). I'll order a second 2mm plate. Shame because it runs really well full chat but as soon as the revs drop under load, it starts pinking.
User avatar
By Wheaters
#99257
I don't think my welding is good enough to be adding material to those slots.
You could use some plastic metal putty, such as "JB Weld"....

I've always used the maximum amount of ignition advance an engine would tolerate, because that's when it's most efficient. My tuned Reliant 850 engine was 13.5 to 1, btw! It produced 25% more torque than a standard one.
User avatar
By Adrian
#99265
If reduced comp doesn't work, it sounds like you could use an ignition set-up with a manually-controlled advance/retard mechanism.

Could be your answer?

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A BTH KC1 or Lucas K1F flange mounted magneto would be the easiest to adapt. They're not an immediate fit but will still go on there with minor mods to the magneto and the crankcase. A platform magneto such as the Lucas N1 would also do, though you'd need to sort out a magneto platform for the Indian crankcases. That too is possible.

A.
User avatar
By Wheaters
#99266
It must be possible to keep the existing setup and adapt the centrifugal mechanism to manual advance/retard - but either way it would still need to have the correct advance limits.

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