adv/ret/fixed

bt-h logo BT-H Magnetos Ltd.

A bit of information about old style manual advance, our auto advance and fixed ignition.

The old style magneto were constructed so that the points opened at the point of maximum flux in the windings to get the best spark. Many of the old style magnetos had a handlebar mounted lever that allowed the ignition timing to be retarded for starting so that the rider didn't get the dreaded kick-back. Moving the lever moved the ignition cam to a different position to achieve the retarded spark. Unfortunately this also meant that the points were no longer opening at the point of maximum flux in the windings so the spark is less than optimum. (This is why some bikes are a bugger to start but run reasonably well once they have finally fired up and had the ignition lever advanced.)

Our new BT-H magnetos have a built in automatic electronic advance/retard. Because the retarding is done electronically the spark isn't weaker when retarded at kick starting speed.

You can specify that your BT-H magneto to have fixed ignition but point out that there is no provision for fitting a lever to retard it manually. We would normally recommend having the automatic option as it is no extra cost and there is no spark performance gain by having fixed ignition.

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Telephone: 01455 844244 (Daytime best before 2.00pm)
(Evening: 01455 457382 - 6.00 p.m. to 7.30 p.m. only)

FAX: Please telephone our daytime number first.