Ignition timing

Hi All,

I don't know which ignition timing setting (28 or 31 degrees of advance) to use on my Commando.

Here is the context :

750 cc / single 32 mm Amal concentric with 240 mainjet / Pazon Sure Fire ignition / Jim Schmidt's standard pistons and camshaft / "tourist" use (mainly mountain roads) / NGK B7ES spark plugs.


Thanks for your ideas about the setting (and maybe about sparkplugs brand and type).

Laurent

Stick with the Pazon installation recommendations.

31 degrees is the setting for electronic ignitions such as Boyer, Pazon etc. However you would need a Dyno to notice the difference between 28 and 31. I cannot, some riders may be able to. I would guess that it will have an effect on combustion temperatures though. Commando plugs should be BP7ES projected electrode but plain old B7ES also worked well in mine at one time.

I agree with Keith1069 that you cannot tell the difference .... however, consider the octane rating of the fuels in your area and your CR, you might lean towards one or other. High CR and low octane, go with 28, otherwise 31.

As a side note: It has been my experience with "hopping" up engines, that go faster modifications will benefit from more advanced timing than factory recommendations, providing the octane rating of the fuel is up to it. Way back in the early 60's, I built a Ford engine to produce over 1 HP per cubic inch. It required such high ignition advance, that I had to fabricate my own distributor rotor, as the standard rotor did not register with the high tension pickups in the extremely advanced condition I found to be optimum.

Slick

The only real difference between 28 and 31 degrees is 3.

The engine may well be at some other position, the timing scales are rarely even close. I needed to degree in a cam for a '75 Mk3, I decided to check the timing scale while I was at it and found a 4 degree discrepancy; in fairness I had fitted a Sparx rotor; a quintessential example of Chinese manufacturing, as has been pointed out in numerous threads.

My point is that before you split hairs on the timing scale, calibrate it, then realize that the timing chain goes through some gyrations as the cam lobes jerk it one way then another as it turns. The higher the RPM your strobe can tolerate will increase the load on the chain and mellow out, to some degree, the fluctuations in the timing picture. Timing a Norton and playing horse shoes seem like proper bedfellows; I suspect the "close" is good enough.

BUT

I'd like to hear from members that have developed a procedure for confidently setting their timing.

Bill.

If the engine is near Combat fast burn spec, ie; 10:1 CR, it may like 28' better for power and no kick back kick or ES starting or detonation. If standard engine specs like most of what these electro ign's sold for then standard instructions of 31' would apply. Its takes degree wheel indexed crank and about dead on TDC finding to really trust the timing light method, so I get em close enough to start then creep up adv till hints of back fire then retard to none then nip up and see if I can detonate/ping on the climate, conditons and octane, then mark the setting and then might put a time light on for a number to share.