Alright, I've been fighting this one for a few months now, and frankly I'm sick of it. I now bring my problems to you guys... I got an '84 F150 4x4 Shortbed. She had a 302 I blew up so I replaced it with a brand new 351W. This engine was built with a Flamethrower distributor(two wire hook up), Accel coil and wires.

After I got done putting it in about two years ago everything ran great(except the carb... another issue) I hooked up a tach, no problems. Then roughly 5 months ago my distributor had a loose ground inside, so I had to rip it apart and fix that. After that, and maybe even a litle before my ignition seemed to be jumping. A wild ignition I guess. now after some research and some digging I found that my coil was leaking, a common source of this type of issue. Also the engine was dieseling a bit after shut down.

So, replaced to coil, pulled the distributor numerous times to check it for and bad connections, etc.. The ignition is still jumping, I can watch the tach flucuate anywhere between 200-800 rpms. I haven't a clue what this could be. I even spoke to a NHRA mechanic from back in the day and he is stumped(without looking at it personally)

So, any ideas fellas?? A wild ignition with all new parts? Could the dist. be shot? I'm lost here.

Thanks for any input!
SMS888

 

Firstly I'd check vacuum lines, hunting idles can be caused by vacuum leaks. I personally think the flame thrower dist are junk, I'd get a MSD with vacuum advance. Accel coils are not the greatest either, but once you get a good one they do last.

 

I actually have a cracking cap on a vacuum port on the carb, suppose that could be it?? I will check all my line though. Thanks, didn't even consider vacuum.

SMS888

 

Absolutely, vacuum leaks will cause major head aches.

 

Wll thanks again, and thanks for the increadibly fast reply... Hopefully this will do the trick. And as soon as I can afford to, I'm switching over to MSD ignitions and getting a better carb. Thanks

SMS888

 

Ok, so... Finally got around to doing timing and attempting to hunt down my vaccuum problem. Here's what I found- when I do the timing with the vac port unplugged on the distr. the engine runs ok, idles fine (with the exception of the carb out of whack). However, when I plug the vac port back into the distr. the engine runs all nutty like I described earlier. You can watch the tach bounce. It's a little ridiculous, but what does this mean??? Is the vac pod on the distr. shot? Or do I have a vac leak elsewhere? If so, how do I track down a vac leak?? Is the vac advance on the distr likely to be an issue? But like I said, with the vac port unplugged, it runs good w/o vac advance. So what do you guys think? Thanks for the help!

SMS888

 

On most Fords, the vacuum advance to the distributor is hooked to ported vacuum. This means there is no vacuum at idle to the distributor. If you are plugging and unplugging in the vacuum line, and it makes a difference at idle, either you have the vacuum advance plugged in to manifold vacuum, or you have it plugged into a ported vacuum source on the carb like it's supposed to be, but you have the idle set too high. The high idle setting will also cause the dieseling you were complaining about.

What number are you setting the timing to?

 

Well, it is plugged into the carb port. Idle is and was set to about 850 and my initial timing is supposed to be 15deg. This is how it came when I bought the engine. It ran great before this happened. It was an all of a sudden thing that. It happened a couple of times a few months ago but seemed to go away after a little while of driving. The dieseling was from my coil that was shot. The coil was leaking and basically falling apart. It hasn't dieseled since I changed the coil so... I don't know. Thanks for the input.

SMS888

 

15 degrees initial might be a little too high depending on the vacuum advance you are using. If you unplug the advance and it runs better, than that is a sure sign your timing is a little too far up. I have run engines up this high, but had to disconnect the vacuum advance, or adjust the vacuum advance so it didn't advance so much. So you have two choices if you want to experiment. Turn the timing back down till it runs good with the advance hooked up, or keep the timing up high and get an adjustable vacuum advance unit. Be warned also that running the timing up that high may make it hard to crank when it gets hot in the summer.

I know you have been running it that high before with no problems, but apparently something has changed somewhere, and 15 is unusually high for the initial timing. The factory setting is probably around 8.

 

I agree with you on the timing. 15 seemed a bit high but any lower and the engine runs kinda crappy. But i guess i'll have to toy around with it. I have a feeling that the distr. is the problem seeing as how i have had to tear it out and apart about 4 times in the last 6 months. Either way, thanks for the input, I'll get to tinkering as soon as the rain stops...

SMS888