Just wondering what setting for the ignition timing anyone may be using on an A65 fitted with an A10 crank?
Hi,
The A70 timing is 37º to 39º and the crank is only 1mm longer on the stroke than the A10 so that is a good starting point. Om my bike with A70 crank I split the difference and used 38º. However, SRM recommend reducing timing advance by 2º due to modern fuels.
Dave.
I initially set my Thunderbolt (823cc with A10 crank and B44 pistons) to the standard 34 degrees as per the A65, That engine is really smooth, I've still not got the jetting right just yet but its a real pleasure to ride.
For What it is worth, I am using the Trispark ignition on it. I think this helps somewhat as it wasn't as smooth with a couple of other ignition systems I put on it.
My suggestion, would be to start off at 34 degrees, if your alternator rotor is sound and located in the right position, you can strobe time it to set the starting point. You can then advance it gradually until you find its sweet spot.
Thanks gents, mine was originally a Devimead 830 which never seemed to run very nicely once 4* disappeared, so I put standard barrels on it and have always run it on normal A65 timing. Then I saw that the A70 was quite a bit different, hence my question.
Oh and I've always run it with Boyer and Suzuki twin spark coil.
The A70 has a higher compression which might explain the more advanced timing in the book, Triumphs used a more retarded ignition timing on their 650's. However their combustion chamber shape is terrible compared to A65 motor which is less like an apex roof compared to the triumph.
Not sure what T140's used but their combustion chamber is more like the A65.