My 1975 230 4 cylinder is supposed to be set at +10 degrees. At that setting it backfires out the intake when I first start up. At +25 degrees it starts up without backfire. What is the highest setting I can use and what will this cause?
I have switched to a electronic ignition setup.

csp,
Upon reading your post, the first thing that came to my mind is that maybe your valve timing is a little late. (experts will surely tell me and you if I am completely off track). But, as far as iginition timing goes, if your not sure...listen to what your engine tells you...does it ping even upon light acceleration? if so, retard. If it pings just a hair upon heavy acceleration, leave it be. How does your new ignition determine when to advance the timing anyway? vacuum? if so, maybe a thermally motivated vacuum valve could be the culprit.
-just taking an amateur stab at it
-Larry

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03/83 300D 184k
07/73 280 160k