My '86 F-250 was running fine then it quit. I determined that the stator was faulty and replaced it with a Borg Warner unit. The engine runs good with the vacuum advance removed and plugged. However when I connect the vacuum advance, it runs rough and backfires. That is with the initial timing set at 10* (the sticker on the radiator support says to set it at 8*; yes I tried that...it ran worse.) This engine is pretty much stock except for the MSD ignition unit (yes, it passed MSD's test), Edlebrock 600cfm carb, and Doug Thorley Tri-Y headers.

Just for the heck of it I reconnected the DuraSpark ignition moduel. It ran even worse so I reconnected the MSD 6A (of course the plugs were still gaped at the 0.060 MSD recommends for this application.

I am open to any and all suggestions.
Thank you.

 

By 'stator' you mean the pickup inside the distributor, correct?
How did the distributor gear look when you had it out?

What coil are you using?
Did it run properly with the vacuum advance connected before the ignition failed?

I wonder about the condition of your timing set, or cam timing in general.
How many miles?
Stock nylon gear?

 

Thanks for responding. I figured it out. The harmonic balancer has "slipped". My friend who is way more savy than I when it comes to engines remarked that this may have happened. I remembered that when I was turning the crankshaft by hand I noticed the elastomeric material showed signs of degradation. So, I went out there and pulled No. 1 spark plug and placed a screwdriver in the hole. I had my son feel for the piston while I turned the crankshaft. We settled on TDC of No. 1 on the compression stroke. The pointer was pointing at 18* BTDC; it should have been on the TDC line. Time for a new harmonic balancer.

Yes, the pick up coil. The distributor gear looked great. It is a stock coil. Yes, it ran very well. Well enough to tow my 3500# boat & trailer up the Grape Vine here in So. Cal. with a 2500# camper in the bed. It has 74K miles and I believe that this engine has a steel timing set, but I could be mistaken about that.

Thanks again for responding.