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O-290-D2 Ignition Timing

Rich Pulman

Well Known Member
Sponsor
I have an O-290-D2 on my RV3. The ignition timing is currently set up at 25°. I recently noticed in the Lycoming operator’s manual that it should be at 18°. The engine seems to perform well enough, but I’m wondering why the D2 and D2A are the only two engines in this series that have a different timing setting. Can someone educate me please? Also, is there any reason why I should not leave it alone? I.E. is there some kind of hazard in leaving it at 25° instead of changing it to 18°?

Thanks for any advice and/or information you can provide.
 

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I can think of 2 possibilities.

1 It has/had a higher compression ratio, so needs less advance for 100LL
2 It was for 80 octane fuel and thus the lower advance
 
Thanks Ed. Good information. I think I’ll leave it alone at 25° since it seems to be working well and I’m not using 80 octane fuel.
 
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