I have a 360 with near stock cam and MSD 6a box. Engine has good vacuum at idle. I have been having some ignition issues with it. First it would not spark one day when trying to leave. Each stage of my problems I tested the MSD box and it seemed to do what MSD said it should. It apparently turned out to be the reluctor wheel was corroded causing the pickup coil not to break the signal, it also had some plastic parts fall out of the distributor while I had it removed so I ordered a distributor to replace it with. Cleaned the reluctor wheel up and ran fine for a while. This vehicle is kind of neglected so I kept driving it with off and on hard starting. Finally one day it would not start. Tinkered with it and finally got it to start and made it home. Finally (about a year after I ordered it)I installed the new distributor along with a new Accel coil, wires and new plugs. Cranked the engine and set the initial timing to about 8 deg. revved up the engine with the vacuum advance off and sounded good. Hooked up the vacuum advance to the ported vacuum and gave it some throttle and it spit and sputtered and backfired. Timing seems to be all over the place. I don't have a good timing light so I used a paint marker on the balancer to get a relative idea of where the timing was going. I painted marks that should have been close to 30 deg and with the vacuum advance it would go to a point that I couldn't see them anymore. Take the vacuum advance off and it seems to run fine. Hook the vacuum advance to full manifold vacuum and spits and sputters. After this long paragraph I am now starting to wonder is it something else that is causing the surging and backfiring or do I still have some sort of ignition problem?

Timing without the advance hooked up should be around the 12-18 degree mark. Back the timing up when you hook up the vacuum advance and see if that doesn't fix the problem.

I had same issue 20 years ago. Same situation but I would put cam 2 in it from time to time & it ran like a scalded dog. My problem was balancer slipped so timing mark was off.

I would (1) hook the can to ported (2) check rotor phasing (3) confirm the can don't have a leak, somewhat rare but I would check it

Stumpy - so you think I should advance the timing more and see if that helps?

RapidRobert - What do you mean by rotor phasing?

when the coil fires you need the rotor blade tip to be fairly close to the cap terminal cuz if that distance is too great the spark cannot jump it repeatedly & it will act up which is seen as a misfire and only the can alters RP. the can is causing the problem (one way or the other) so with it on manifold it may cause a problem at idle (just too much timing) but I was thinking it was above idle. the can may or may not be shifting RP to where there is a problem. rarer is a leak in the can diaphram causing a lean misfire. As Stump said get your timing to a reasonable baseline & I would highly suggest plugging the can into ported & see what develops & holler back. EDIT Are you saying you dont have a dialback? (1) degree is 0.0632683" around the dampener circumference and you can cut/measure a strip of newspaper with your calipers & make black ink marks on it to use it as a ruler to make new white paint marks on your dampener, IE 17.5/20/22.5/25/27.5/30/32.5/35 degrees. for example 17.5 deg is 1.107" (CW from the OE TDC slit) MORE EDIT I reread & it sputters on ported or manifold. I'd cap the can & set initial at 15 for a start then plug the can into ported (I'm assuming your idle speed is low enough so there is no vac at your idle speed at the ported nipple) & try it

Actually you should retard the timing if you have it at 30*+ with the vacuum disconnected. Connecting the vacuum advances the timing.

don't forget, if you increase the initial a bunch, make sure you remove some from the total so you end up with somewhere around 34-38* at WOT with the can disconnected. as to how fast the total comes on, that is determined by the weight springs. you will need to experiment with these to find out what works best for you. when you accomplish that, then start playing around with the vacuum advance. that only comes into play at a low/no load condition. you should be able to use around 40-50* or so total timing on the vacuum advance at a steady, NO LOAD cruise. EACH engine/vehicle/fuel combo can and will be different, so experimentation is the ONLY way to find the sweet spot for your combination. different cans are available, and don't forget that the diaphragm inside the can is able to be adjusted as well. ebooger did a comprehensive article on how to adjust timing for mopar action several years ago. it's well worth reading and implementing. and when the vacuum advance is dialed in correctly, you will benefit from increased gas mileage.

8 degree at initial is way low and would cause the sputtering and poor running. I 've found mine like around 16 initial

Just FYI the problem ended up being the MSD box itself. I hooked all the factory stuff back up and it ran fine. Just thought some of you might like to know what the final answer was.