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SP250 Distributor markings and timing for 98RON fuel

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Jez
Posts: 89
Joined: Mon Feb 15, 2016 8:00 am

SP250 Distributor markings and timing for 98RON fuel

Post by Jez »

I recently completed a rebuild on my MGB engine and whilst setting it up found that, using 98 RON fuel, running the timing a couple of degrees more advanced than standard gave best results in terms of both stable idle and power delivery. Given the slower burning nature of modern fuels and increased anti-knock from the higher octane fuel that seemed to make sense. It got me thinking about the Dart, and I experimentally used the micro-adjuster on the distributor to advance the timing a little from the standard 10 degrees static.

I can't tell any difference at idle but the engine subjectively seemed a little livelier. I was curious as to whether anyone else has done any testing or has any recommendations around this?

Also, does any know the timing change per graduation mark on the distributor adjuster? It's clearly marked for Advance and Retard but I can't see in the manual or the forum any reference to the actual timing change. From some quick measurements and maths it looks like each mark may be a distributor degree ( 2 crankshaft degrees ) but it would be good to know for sure!

Cheers - Jez
Jez Stow
1960 Daimler Dart
and a few other toys

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