Boyer ignition question.

Greetings,

After 26 years the Boyer crapped out on my 72 Intestate. I ordered a new one and the instructions said to set the engine to 31 degrees BTDC.
The book list 28 degrees BTDC as full advance.
What's up with that?
I left it set to 28 BTDC.

Yes, it's normal to set the Boyer to 31 degrees. 28 degrees is for points although the Boyer seems to work at 28 degrees.

About 20 years ago I did a lot of experimenting on a dyno with varying ignition timing. Norton twins seem to have a very good combustion chamber shape compared to say Triumoh twins. Varying full advance between 28 and 31 deg seem to have no repeatable significant differences on my bike. Getting the carb right was more important for optimal performance.

However I have read some motors do prefer less advance with higher compression, different piston crown shape and squish if any.

johnm said:

About 20 years ago I did a lot of experimenting on a dyno with varying ignition timing. Norton twins seem to have a very good combustion chamber shape compared to say Triumoh twins. Varying full advance between 28 and 31 deg seem to have no repeatable significant differences on my bike. Getting the carb rightward more important for optimal performance.

However I have read some motors do prefer less advance with higher compression, different piston crown shape and squish if any.

Click to expand...

I have to agree, before fitting the Alton system, i had the timing set to 31BTDC, (with a Pazon EI) and to be fair every now and then it kicked back good..
But after reading the Achilles heal issues with the Alton system (shearing plastic drive dowels) when it kicked back, i chose to knock mine back to 28BTDC..... and to be fair i cannot detect any difference with this 3 degree reduction.
Yes if is was on a track, or looking for ultimate performance then I'm sure it would make a difference, but as I'm not 28BTDC is good for me

Because the analog Boyer advances too slowly in the lower RPM range, I think the more advanced the better if it makes little difference at the top. Nortons with points seem to have more low end torque in my experience.

The lore of why Boyer specified 31 degrees at 5000 RPM was because the black box ignition never stopped advancing (logarithmic advance curve), therefore a stop gap was to set it 31 at 5k so it would be more in the sweet spot traditional 28 degrees at lower (i.e. every day riding) rpms. Points are at full advance at 3k. A good ignition has a programmable curve and can be set to full advance anywhere along the range. Tri-Spark and Pazon have a very fantastic curves right out of the box in this regard.

Racers often flipped the trigger leads on the Boyer, thereby eliminating the logarithmic curve so it would always be full advance, and timed their bike appropriately based on where they wanted that full advance

Another thing about Boyer that folks often confuse (Comnoz schooled me on this one at the track some years ago): Black Box Boyers use the battery to RETARD the curve, not advance, as many (me) assumed. So when the battery goes low and becomes ineffective the ignition goes way advanced. Thus it kicks back. Imagine this on a MK3 Electric Start Commando in 1975 with an original Boyer. The moment you hit the starter it pulls deep on that battery and advances the hell out of those old Boyers. I think the Norton sprags and "electric assist" got a lot of bad rap due to Boyers acting up when that starter motor pulled hard on that battery. And thus, Pazon was born.

Holmeslice said:

...Black Box Boyers use the battery to RETARD the curve, not advance, as many (me) assumed...

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Some of the advance curve is affected by the electronic circuit, but much of it is due to Faraday's law of induction which states that the field is proportional to the velocity of the magnet. This causes the threshold voltage in the pickup coil to be reached earlier with increasing RPM. DynoDave's experiments showed that when a Mk.3 falls below about 10.7 volts, the timing gets increasingly erratic with error bar width proportional to the drop below that voltage.

Regarding flipping the polarity of the stator wires: there seem to be two versions of the Mk.3: one version gives fixed timing (which I've only read about) and the other gives a reverse curve that advances with falling RPM (which I've witnessed myself.)

10drum said:

Greetings,

After 26 years the Boyer crapped out on my 72 Intestate. I ordered a new one and the instructions said to set the engine to 31 degrees BTDC.
The book list 28 degrees BTDC as full advance.
What's up with that?
I left it set to 28 BTDC.

Click to expand...

If you set it to 28 degrees the header pipes will turn black , and be searing hot , 31 degrees on mine, runs great .

Thanks for all the replies, great discussion.

All of my British points bikes have Boyers. I haven't given them much thought, just that they worked.

I am getting a carbureted new bonneville back on the road and have been wondering about the ignition, and why it uses a throttle position sensor.

Just like the boyer, tri-spark, factory, or whatever computer/electronic ignition system is used, I'd like to see/research the line by programs that are written into them. Yeah, I know I'm a gluten for punishment, or just bored.

When I looked into electronic ignitiuons to replace my Boyer (as something was just not right), I asked Steve at TriSpark for the ignition advance curve.
I was happy that when I set max advance at 28 degrees, the under 500 rpm timing would be ATDC which would protect my Alton from kickback.
What was surprising is that before the TriSpark, it would stall when cold. But after I put on the TriSpark, and had not touched the Mikuni, it did not stall when cold and idles quite well
Dennis

If you do not change the fuel, three things affect affect combustion conditions - compression ratio, ignition advance and mixture. They form a balance, and an optimum can be achieved by adjusting any one of them. If you raise the compression ratio by over-boring the motor, it has the same effect as leaning-off the jetting or increasing the ignition advance. I usually set the ignition advance to 29 degrees and adjust the jetting without changing the compression ratio. Bob Rosenthal adjusts the jetting using an oxygen probe, then moves the ignition advance to get maximum torque while the bike is on the dyno. Either way is not rocket science - we just need to think systematically.

I always try to avoid moving the ignition advance, changing jetting is a pain.

DennisMo said:

When I looked into electronic ignitiuons to replace my Boyer (as something was just not right), I asked Steve at TriSpark for the ignition advance curve.
I was happy that when I set max advance at 28 degrees, the under 500 rpm timing would be ATDC which would protect my Alton from kickback.
What was surprising is that before the TriSpark, it would stall when cold. But after I put on the TriSpark, and had not touched the Mikuni, it did not stall when cold and idles quite well
Dennis

Click to expand...

When the Boyer crapped out I looked into the tri-spark, it was double the price of the Boyer, This bike has ran great the 5 years I've had it, so I couldn't justify paying the extra $$$.

10drum said:

Greetings,

After 26 years the Boyer crapped out on my 72 Intestate. I ordered a new one and the instructions said to set the engine to 31 degrees BTDC.
The book list 28 degrees BTDC as full advance.
What's up with that?
I left it set to 28 BTDC.

Click to expand...

You likely have a combat engine in your ‘72. Leave the timing at 28degrees BTDC unless you are using 100 octane leaded fuel.

10drum said:

When the Boyer crapped out I looked into the tri-spark, it was double the price of the Boyer, This bike has ran great the 5 years I've had it, so I couldn't justify paying the extra $$$.

Click to expand...

Pazon is similar price to Boyer, but better with low voltage.
The Wassell's Vape is cheap and has positive reviews, but I haven't tried one on a Commando yet.

ALL of the commonly used kits are cheap considering what they do and how long they last.

The difference in price should not be anyone’s prime decision making factor IMO.

Boyer MK4 has the Pazon low volt mods, the Boyer MK3 does not.

kommando said:

Boyer MK4 has the Pazon low volt mods, the Boyer MK3 does not.

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Yes, i read that, but the Mk4 on my last T160 wasn't great at starting on the button.
No hint of kickback, just a weak spark. It kickstarted just fine, and sometimes fired up as soon as the button was released.

I had an older new Boyer back in the early 80s (33+ years) was still going when I replaced it about 12+ years ago with the Joe Hunt magneto in all them years of running with the Boyer I never once got any kick back from kicking my Norton over, I can't understand why so many have problems with kickback, my first Boyer installed about 1979 the black box stuffed up from the great fire of 82 and the Boyer that I had for 33yrs was it's replacement, never touched in in those 33+ years of running with it except for new batteries when they died and 2 coils.
I have never used a timing light on my Norton in 49 years of ownership with the Boyer and JH I set the static timing then when running I advance the timing till I get a little kick back then ever so slightly retard the timing till no kick back, this has worked for me, my Norton has always ran well doing it like this.

ashman said:

...I can't understand why so many have problems with kickback...

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There is significant manufacturing variation between Boyer analog units giving different advance ranges spanning several degrees. I could see changes in spacing between the rotor and stator causing additional advance range variability.