"Yep, you have a pcv valve.
I
"Yep, you have a pcv valve.
I assume when you say manifold, you are talking about exhaust? I would not think a leak here would cause a backfire thru the carb. However, a leaking exhaust can cause a explosion or fire, best replace the gasget.
With a new coil and still backfire, even tho you have a new dist cap, take a look at it again for any moisture. It is possible for fumes to come up thru the dist shaft due to bad seals or a plugged pcv valve would allow crank pressure to work its way up thru the dist shaft.
I have purchaced new caps with cracks from the factory. After you are sure the dist cap is good...
Now, as for the backfire thru the carb. Is it more like a spit similar to opening a fizzed up beer can? It could indicate a lean carb. Vacume leak thru the carb base gasget is typical. It is also easiest and cheapest fix when dealing with carbs. Using a can of spray carb cleaner and engine idling, give it a quick squirt around the base gasget and be careful spray only the base gasget area. If the base gasget is leaking, the engine will increase rpm's and then slow back down. If that happens, tighten the carb mounting bolts and test again. You may have to replace gasget if tightening fails to stop the leak. If rpm's dont increase than the problem may be internal to the carb. A bubble of water rolling around the float boal partially plugging the main jet (water will not pass thru the main jet easily) or a partially pluged power port gizzy, sticking float seat, low fuel level in bowl. A small bubble of water or crud can be blown away from the main jet due to the back pressure of the "backfire/spit" and eventually work it way back again for a repeat.
If you have never rebuilt a carb, it is bet to give it to carb guy.
If you get as far a rebuilding the carb and you still have a backfire problem than you have performed all the cheapest and easiest tasks, coil, wire, plugs, dist cap, pcv etc all that is left would be a funky valve. One of 16 and very difficult to decide which one. A rebuild of 2 heads is the most expensive and a total head job in a shop could be around $500 if they use all the old parts add another $100-$150 for a gasget set to reassemble the heads, manifolds,etc.
Taking the heads to a shop, they will rebuild every part of it to factory specs hence the $500. Do it yourself, you can do nicely by taking it apart, cleaning everything and if the valves are not burned, just hand lap them and reassemble for the cost of head gasget set. Only special tool needed is a valve spring compression tool you can probably rent from a tool rental. Oh, you will need a torque wrench for the head bolts, intake and exhaust."