Spark plug condition and backfiring

[Dave in Denver]

I have a 1930 Tudor, 4 banger with Snyder 5.5 head, fed by a zenith updraft and sparked with a petronix distributor. Living in denver at 5000 feet.

Been trying to get this rebuilt engine running. I am certain my timing is off a bit, but the real issue seems to be the spark plugs. I gapped them at .035 and started the car, adjusted the timing (approx 20 degrees advanced) and the carb but at anything over 1200 rpm it backfires through the carb.

To check things, I pulled the plugs. #1 and #4 are very black sooty, while #2 and #3 look normal.

Question: might I have some sticking valves on #1 and #4?

Or what else might be happening.

Thank you in advance.

Dave

 

[Fred]

Go back to the original dizzy & all will be good..

 

[Purdy Swoft]

Check your firing order, its easy to get 3&4 crossed with a modern type distributor or cap. The model A firing order is 1243. Your spark plugs may be too cold. Champion W18 work best for me. If you are using adapters for 14 mm plugs AC R45XLS is a good hot plug , this is a 14mm long reach plug. I use them in my speedster and my daughters coupe both with Mallory distributors. Try 28 degrees on the timing.