Hitchcocks Forum

hi I have fitted a Lucas sr1 mag too my Indian 350 bullet with a auto advance unit and I was wondering what I should set the timing at any help would be grate many thanks.

Try 3/8" to 5/16" before top dead centre full advance. That should get you about right.

REgards, Mark

Hi S1 should be 7/16 to 1/2 inch BTDC fully advaced

Trust this will help

Well I am not a Bullet owner but our hosts tech info gives 8.5mm (21/64") 32deg fully advanced and this will be the same regardless of what makes the spark.

They've been printing those 32* timing specs for almost as long as those (now accepted to be) incorrect tyre pressures.
32 degrees on full advance is absolutely fine for 1950's petrol, for everyone else using modern UK fuels developed in this century some six decades later a little more advance is quite beneficial.
When I had my bullet on the Dyno and rotated the back plate to advance and retard the (full advance) firing point the ignition setting where the engine produced maximum power was found to be exactly 38* (1/2" BTDC).


HOWEVER it was found that whilst 38* produced a noticeable increase over the oft quoted 32*; 39* of full advance produced a noticeable drop off in performance so unless you have a reliable method of accurately setting the fully advance firing point and a stable ignition system to ensure the firing does not advance beyond 38* BTDC then erring on the side of caution and opting for a lesser amount of advance might be prudent to avoid engine damage - just sayin'

I do not wish to say if the tech figures given by our hosts are right or wrong but the advice re petrol is not!, leaded petrol had a slower burn rate than modern non lead/ethanol petrol and without exception I have to set the ignition timing on all the old bikes I own or work on 2 to 3 degrees retarded to compensate for the faster burn.

"THEY" in my post refers to the Indian factory literature and for clarification I really ought to have added that UK 95 octane fuel ie standard unleaded non ethanol supermarket fuel was used during the Dyno run when setting the Ignition on my Cast Iron Barrel Bullet (so thankyou for the memory jog revband).
Using the Dyno method to set the ignition timing will always provide the definitive answer as to what the ignition timing should be with whatever fuel is being used at the time of testing.


As we should all be aware, that even with these fine hand built engines so carefully built in the Royal Enfield factory in India that some degree of variation could occur during assembly and as such individual results between engines could vary.

Ric, you seem to have about as much faith in the Indian Enfield factory as I do, 😁

Thank you so much for all the help I will give it a go many thanks.

My 350 has an SR1 with a lucas auto advance unit. It is set to 1/2" BTDC with the bob weights pegged open and it goes like a charm on modern unleaded fuel.