Well it's impossible to tell anything about the points from a picture like that. Do the contacts look burnt? May want to replace. Best to use a dwell tach to adjust point gap.

Motorcraft still offers quality points and condensers. If you are going to utilize the old school mechanical ignition systems you must use good ignition parts. The otto zone stuff is junk and should be avoided. The distributor must be in good shape with no excessive slop or runout wobble.

The problem with simply measuring ohms in an ignition coil is that the variance in the secondary (where shorted turns are likely) resistance isn't enough necessarily to be noticeable from spec unless prior measurement was made. Mechanics used scopes back in the day and defective spark could be identified and isolated right away.

 

The distributor and all contacts in it look really good with a little bit of carbon on the rotor (and I mean a little bit) the reason I'm jumping to conclusion on the coil is it looks to be really old. It's covered in grease and looks to be original

 

From what I can tell, this is the original coil, judging by the yellow top and the autolite branding and part number, can someone give me thenough ohm resistance?

 

That sounds to me like it could be a fuel boiling issue. After you shut off the engine the hot manifold heats the carb and the fuel. Causing it to boil over into the engine and flooding it.

 

The issue was the coil, took a shot at since it's original and I'd have to replace it soon anyways, the new one fixed my issue! And I don't have any boil over issues, the closest the fuel line gets to a manifold is about 16 inches away as its ran next to the engine mount

 

Good deal. Sort of figured it had to be coil or condenser, based on the symptoms you reported. Measure the voltage at the new coil while idling, should be around 7 or 8 volts.

edit: Yes the picture of the coil shows the internal oil (used for cooling) leaked out. One way that might happen is if the points happen to be closed and the ignition switch left in the RUN position with engine off. All that primary voltage has nowhere to go.

 

Good job guys....what a bunch we have here.

 

Wait don't get too happy now. Trucks idle is fluctuating again. Unsure of why. You give it a quick blip of the throttle and it'll raise the rpms and then slowly start fluctuating more and more. Something I noticed since it started idling bad is a puffing sound, but it just doesn't sound likes it's from the carb

 

This is making my brain hurt, I'm just somewhat hoping it's a carb issue so I can convince myself to swap in a 1850 and a 4 barrel intake

 

Just for general information, it's not unusual for new points to loose their gap after about 500 miles or so. This is because the rubbing block wears away. It seems to be more common now than back in the day, due, in my opinion, to the lower numbers produced and faulty rubbing block material. That can also cause backfiring. As you found out, a coil can ohm out ok and still be faulty. Glad you found it.

 

So what could be a likely cause of fluctuating idle? The truck runs fine still it seems, but it won't stay at 600, it'll drop down to about 300, jump up to 700 and back down, slowly dropping till it stalls out

 

Could be a bunch of things. The contact points as mentioned, or idle mixture screws, bad power valve, vacuum leaks, float level, etc.

 

Float level is fine, tomorrow morning I'm gonna tinker with my vacuum gauge and see if my idle screws are just that messed up. Is there somewhere in the carb that could cause the pulsing whosh of air?

 

A/f adjustment would be my first guess is on the lean side. But many little things can add to rough unstable idling. Check all vacuum lines at where they connect to.

A split on a barred nipple will crack where you can't see it. To insure a good vacuum line, cut about a 1/2" off the tip of a hose with a barred end hose. Maker sure carb bolts are tight.

Same for power brake booster vacuum hose. And if it's auto trans there's a vacuum line that is or was half rubber & steel line going down to a little modulator. With a short rubber hose that can split sucking air.

And if the modulator goes bad the tranny won't shift right plus suck fluid into the intake manifold which will make the engine smoke.

It's best to go back and recheck all the timing setting and adjustments carb with a vacuum gauge. Also reset engine rpm for your type on tranny should settle the rpm's. If rpm to low it will start floating rpm around then die.
Orich

 

Also what I was trying to tell you to check is the plate the points mount to. See the arm that goes between the vacuum can and the points plate? That moves/rotates the points plate to advance the timing. If the plastic bushings the plate pivots on are loose it will cause the points gap to vary enough to affect the ability to accurately fire. The points gap should be about .017, so if the plate has even just a few couple thousands of slop it will vary your points gap that same couple of thousands. If it's bouncing around it will cause an erratic idle.

The system of points is pretty primitive, everything "touches" (points contact each other, open and close by contacting the block), and is subject to a lot of wear in a short time. Don't get me wrong, I still have a couple of motors running with points in them just because I can but the next generation of pickups in the mid 70s evolved away from using contact points and went to a magnetic signal that eliminated anything touching. To make the distributor function reliable in this truck you need to make sure the plate doesn't have slop and use good quality points. The points gap needs to be accurately set, adjust it with a feeler gauge and the points need a small amount of lube on the contact block to help reduce wear and keep the gap consistent.

Your cap has a lot of tracking on it, that is from normal wear but it also indicates resistance that your coil would have to overcome to fire the spark plugs. By today's standards the points system is pretty weak so it needs all the help it can get; in other words you need to replace that cap and rotor as part of a good tune up. You probably know how a new vehicle can run well over 100,000 miles and never even get plugs, that's because of the improvements in the plug tips and things like individual coils for each cylinder, stuff our trucks just don't have.

If you look at where everything is now it's pretty interesting to see how the engineers have addressed the problems and improved the reliability. But when it comes down to it if I were on the side of the road with a no start I'd much rather have your truck than any computer controlled EFI pile that I need a computer to diagnose.