I have set the timing at 7.5 degrees at 850 rpm; replaced the points and set dwell to 30 degrees, but am still getting backfiring through the carbeurater. Any suggestions of what to do next? THX JM

 

Did you disconnect the vacuum advance at the pot on the distributor before setting timing?

 

Welcome to CO.

 

Yes, I did and then i reconnected the vacumn advance afterwards. I am going to repeat the process. THX

 

I assume it was backfiring before you did the tune up? Has the timing chain and gears ever been replaced? Might look there for your problem.

 

Does that mean that the chain gets stretched and the valves open at the wrong time? I think this engine has a steel timing chain. Where would you even be able to get a new one?

 

What is does is throw your timing off and you can't adjust it correctly because it keeps changing do to the slack in the chain. You can buy a timing chain and gear set at Rock Auto on the internet or at any quality auto parts store

 

Is dwell 30 degrees or 20 on these, been awhile?

 

30° +/- 2°.