so i've got the 390 in my 75 f100. I've had timing issues since I've bought it back in july 2010. I've had the timing set to 12btdc, pinged, and pinged a second time leading to the distributor gear pin to shear. Fixed that, set it to 10btdc and never drove it enough to see how it went. Changed the advance springs to have full advance at 3500ish rpm. the slot is set to 10L. Set the initial to 16, too much. Set it to 14, too much. (As in won't crank fast enough to start) Set it to 13, alright. It ran. I drove it around yesterday, PING, WHAT THE ****. After that it didn't sound the same, like it wasn't running on all 8, although no noises were coming from the engine. Set the timing to 10, ping. Set it to 7, and it hasn't pinged so far. This is with the adjustable vacuum advance set to advance slower.

When I listen to the drivers side 4 cylinders firing, there is a slight consistent popping coming from that tail pipe. The engine has a lot less take off power, and seems to just chug along until you pretty much gas it a little and go faster. I really think someone happened to one of the cylinders on the drivers side when the last big ping occurred. Gettin very irritating that this damn thing won't run right. ANY help would be great!

 

forgot to mention also that when you slightly give it gas the engine shake side to side noticeably from whatever is wrong

 

Plug exam and compression test.

 

Plus 1.

 

You do not set timing by initial timing. You set it by total mechanical advance, then you check initial and use that to set your timing from then on. If it isn't pure stock you can not use initial timing because it is just a guess and guessing isn't how it is done.

 

my timing would have been 36 for total with 16 as the initial and using the 10L slot. That's why I set it there at the beginning.

Also another thing to add, I had to drop off the timing considerably to got down to 7btdc. Another reason why I think something happened to one of the cylinders because if i'm right, it takes less timing to turn less cylinders?

 

If you didn't check it you are still guessing.

 

yea true. well i'm going back over tomorrow to check the compression, where originally they were all at 150psi last year. I'll also check all of the vacuum lines too.

 

16 may just be too much initial, regardless of which slot you're using. i'm at 15 initial, and after getting the engine fully warmed up and shutting it down, it doesn't want to start back up.

 

Using 24 volts to the starter always cured those issues on my race cars. But for a street car you are right.

 

turns out that a vacuum port came unplugged. Ran fine after that and I set the initial to 8 for now just to be safe. i'm gonna change the advance springs to the 3800rpm I believe it was, cause right now it seems to advance really quick when i watch it with the light as someone pushes the pedal.