modifying a boyer ignition for less total advance

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Here's an ideal mag setup for racing. This mag has fixed advance timing but comes with a lever to retard it for starting. The lever retards 20 deg.

modifying a boyer ignition for less total advance
 
dorset said:
i did then, but i was running a pazon smartfire with an advance curve set to ordinary timing for a triumph, which is way advanced compared to nortons or BSAs. since then i've switched to fixed advance with this motor and run a magneto:

modifying a boyer ignition for less total advance


the ARD isn't originally set up to fire four spark plugs, but Morris magneto sells forked plug wires with an interior diode that split the energy between two plugs. it runs fine now, but sparks all four plugs every 360 degrees, two power and two waste sparks per revolution.
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Two questions:
#1 Why use the earlier rocker boxes, rather than the 1971 or 1972 style? The later boxes make it easier to do valve adjustments.

#2 Is the guy who made your engine stand still in business? If so, how can I contact him?
 
i use the old boxes because the motor goes into a 1965 frame, and this way the stock early head steadies fit right on. youre right about valve adjustments, though. the cams take 0.008 and 0.010, so i use the 26 tpi adjusters as a micrometer--90 degrees from zero is 0.010. cant get a feeler gauge in there.

and no im very sorry but the couple who built that stand isnt in business anymore, so far as i can tell. they sold them on ebay for a while, and theyre great. the motor is balanced and spins in a complete circle so you can work on all sides at once, and you can pull the top part off to mostly clear the bench. probably a muffler shop could bend one up, if you gave them some cases to measure against.
 
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SteveA said:
Right, I have a Boyer ignition box that has less than 31 degrees advance, like half, why? Well it was supplied by Steve Maney as part of his crank ignition system, so ran at engine speed, not half engine speed.

So my guess would be that the internal circuit was modified in a similar way to adding the external resistor. When the pick up was wrecked I changed it to a camshaft driven pick up, sete if for fully advanced at 5000, ran fine!

But for racing back in the day the ignitions were run with the Advance Retard Unit welded up, which was to prevent the bloody thing exploding, which I had one do!

At that point I acquired a Lucas Rita that had been used by the Thruxton race shop. When I strobed it I could not see any advance, which was because the advance circuit had been jumpered out by Thruxton, Ran fine too!

So I am easily persuaded that running fully advanced is fine for a motor you don't have to kickstart and spends a lot of its life over 4000rpm!

Eventually I changed the Maney Boyer box for a complete Pazon Surefire, it runs fine too!

Best thing I did to boost corner exit was to weaken the needle!
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If you are running on petrol, you probably cannot get fine enough jetting adjustment with Amal carbs,to detect a difference in the ignition advance curve by a difference in power output. Theoretically, if the ignition advances as the revs rise to compensate for the change in rock-over time, you should get a power increase. But at the same tine as it happens when you are riding the bike, the throttle opening is usually changing and the needle jets are varying to compensate for the changes in vacuum. The difference you achieve with a programmed advance curve is probably very small. But you never know until you try it on a race track which you are very familiar with.
Most of the guys on this forum probably run their Commandos slightly too rich. The loss of power is small but detectable. With petrol, the difference between a 0,106 and a 0.107 inch needle jet is very large. But if you run leaner your motor's performance is much more weather-dependent. When you race, you usually take that into account, so you can run closer to the optimum.
 
acotrel said:
If you are running on petrol, you probably cannot get fine enough jetting adjustment with Amal carbs,to detect a difference in the ignition advance curve by a difference in power output. Theoretically, if the ignition advances as the revs rise to compensate for the change in rock-over time, you should get a power increase. But at the same tine as it happens when you are riding the bike, the throttle opening is usually changing and the needle jets are varying to compensate for the changes in vacuum. The difference you achieve with a programmed advance curve is probably very small. But you never know until you try it on a race track which you are very familiar with.
Most of the guys on this forum probably run their Commandos slightly too rich. The loss of power is small but detectable. With petrol, the difference between a 0,106 and a 0.107 inch needle jet is very large. But if you run leaner your motor's performance is much more weather-dependent. When you race, you usually take that into account, so you can run closer to the optimum.
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I run Mikunis!
 
A Mk2 Amal is not much different from a Mikuni. But Mikunis were primarily designed for two-strokes which are much more sensitive to errors in jetting. Because I run methanol, I make my own needle jets for my Mk2 Amals. But with methanol, the jets flow twice as much, so the jet size is half as critical, as it is with petrol.
I originally bought my carbs as modified for methanol. As received, the needle jets and needles were really stupid. An Amal alcohol needle usually has completely the wrong taper. When I had Triumph 650 road bikes on petrol with Amal carbs, I probably never got the jetting right. But if the bike actually started and ran, that was probably good enough.
 
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