Join Date: Oct 2014
Location: Nashville, Tennessee
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Backfires can be caused by too much timing advance and/or lean mixtures.
It does sound like you need to make sure your timing is correct. You can do that with an advance timing light.
With vacumn advance can disconnected and plugged to manifold vacumn, Set the base timing 8 to 12 degrees BTDC thatshould get you running.
If you can then plug your vac can to full manifold vac. (Shut off the car if you have to find that and set it up) and then restart and read the timing. with vac to full manifold for the dist at idle. Now you will know your full vac can timing. Maybe it is 20 more degrees, they usually are way too much.
Now shut off car and remove dist cap, take one spring off the centrifigal weights on the top of dist, under the rotor. Put the cap back on. disconnect and plug the vac line to dist so no manifold vac leak.
Now start her up, you should be running at your base timing 8 to 12, now rev the motor up to 3 or 4000 RPM's and read the timing advance where it stops and no longer advances.
That reading minus base timing that you set by hand already is your centrifigal advance. Base and Centrifigal should be 36 together total you can adjust the base a few degrees to get it right.
an additional 10 would be ideal from the vac can for 46 degrees,....this is for light throttle cruise.
This will tell you where you are if that centrifigal number is real high, and or the vac can is real high, too much advance will cause a backfire, so see wht you have and then you can work to get it right,
Make sure your parking brake is on, car is in Park, wheels are chocked and good to have a helper. Also do not forget to replace the dist spring when your test is done.
Sounds like you may have way too much advance, at least a possibility. Makes for hard starting as well.
Good luck, you will get it, sounds like a great car!