Well I did rev it up a bit if that is what you mean, and it did still seemed to stutter at the upper RPM range. I was particularly looking at one plug boot that is close to a header pipe but still no sign of arcing.

I have new wires coming as these have, as close as I can estimate, about 40K miles on them. IIRC, when I did the DS2 swap I had to dig up a different coil wire because this set used the e-coil wire. Not sure how old that coil wire might be because I don't remember if I used an old wire or bought a new one.

My coil does have the capacitor on the side. I'll disconnect it the next I have the truck out. I'll check this before I change the wires.

 

Check for extreme slack in the chain too. Mine had an insane amount but didn't jump. Had problems in the upper RPM range, IIRC.

 

Yes, that's what I meant for duplicating the fault.

Any good news yet? Given a chance to spend your time and money, here's how I'd proceed, since you've received all sorts of good suggestions taking you in different directions. After making any changes, do a test run in case the symptoms change. I suggest the following order, but that's not super important, mostly trying to rule out the easy stuff first.

1) Unhook the radio noise filter (capacitor) on the coil.

2) Do the AC ripple test detailed in post #42. This is a long shot, but will only take a couple minutes and nothing needs to be disturbed. (Wouldn't it be great if the answer was 42? Bonus points if you know the reference.)

3) Check for slack in the timing chain. Remove the distributor cap. Use a socket and breaker bar on the nut at the front of the crankshaft. Turn slightly in the normal direction, stop, and note where the rotor is pointing. Turn the breaker bar the other way and see how much the crankshaft turns before the rotor moves. More play equals more slack in the chain. This is another quick and easy test.

4) Install new plug wires. Test the engine before proceeding.

5) Install new spark plugs. Use a different brand than what is currently installed.

6) Replace the fuel filter at the carb inlet. Carefully cut the old one open to inspect for blockage or evidence of the pump coming apart.

7) Tee in a fuel pressure test gauge at the carb inlet. Verify pressure is still within specs while revving the engine to duplicate the fault. I put this last because it's a fair amount of work to do, but definitely try it.

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Will try all of the above when wires arrive, (no mail delivery today).

Only new thing I found is that the problem is heat related. I was cleaning up a few things in the engine bay and found that the carb. bolts were snug but not tight so I tightened them down and took it for a run. The first run was up the hill by my driveway (very steep) and engine was only at 160 deg. It pulled the hill no problem clear up to 3200 RPM.

Encouraged, I drove it to a long hill several miles away. This time with the engine at 190 deg., things fell apart on the steep part of the hill at about 2600-2700 RPM. Also noted that the tach. did not seem to be jumping around.

I don't know if this points to anything not previously suggested.

 

The tach not jumping says the primary side of the ignition system is happy, including the pickup, ignition module, and the primary side of the coil. But, it doesn't say anything about the secondary side of the coil, the coil nor spark plug wires, the ignition cap and rotor, or the plugs as they could be bad and the tach not flinch.

Having said that, the only piece of the secondary side that heat usually bothers is the coil, and you've changed that.

 

Well I am back with some new info. As you may or mat not recall, I was experiencing buck/stumbling when trying to accelerate up a steep hill, occurring at about 2800 RPM. Last recommendations were disconnect the coil condenser, no change and change plug wires, also no change.
I finally got around to checking the timing curve and that may be it. This is on a 1984 351W, so relatively low compression. I disconnected and plugged the vacuum advance hose and used a home made timing tape. Results as follows:
Initial timing at 850 RPM................10 deg.BTDC
1000 RPM....................................10 deg. "
1500 RPM....................................13 "
2000 RPM....................................20
2500 RPM....................................22
3000 RPM....................................25
3500 RPM....................................27

As I understand from research, this engine could use 38-42 degrees of total advance and it is desirable for it to be all in by 3000 RPM. So I think next step is check the weights to see that they are not bound up in some way and if not lighten the spring tension.

Does it sound like this could be the problem, basically running out of vacuum advance up the hill and not having sufficient mechanical advance to compensate?

 

Yeah, it sounds like the breaker plate might be sticky, or real heavy springs. Some stock distributors won't be "all in" till 4k or even more. Mechanical should show up (at least some) soon after off idle. I'd shoot for 34° or 36° maybe more, bu it depends on your engine, fuel quality etc though. Experiment.

Remember these numbers are with vacuum advance disconnected and plugged. When going up a hill, the manifold vacuum will go away or at least decline quite a lot. So consequently vacuum advance does too. If the mechanical advance isn't working correctly it will not run well at all, and economy too will suffer. Once you're happy with the mechanical curve, reconnect vacuum advance and dial that in.

With all that, be realistic on how the truck will be used. OEM used a slow advance curve because trucks are meant to haul heavy loads. If you routinely use your truck as a truck - and they aren't light to begin with - your advance curve might not need/want to be so aggressive. But you can improve on it quite a bit and still avoid any knock.

 

Not really, but I'll let somebody more versed in distributors chime in.

"Running out of vacuum advance" isn't a good description of what happens. The vac advance is only present at part throttle operation, to improve economy and emissions. Under full throttle, all vacuum advance is removed (very low or no vacuum muscle force in the manifold). So at full throttle, you've got centrifugal advance only. Heck, my 1948 Jeep has centrifugal advance alone and no provisions whatsoever for vacuum advance. It runs just fine like that.

From my limited experience, incorrect ignition timing causes low power, but not really any stumbling or rough running. You may still be on to something, don't get me wrong, but I cast my vote the problem is elsewhere.

Did you ever run any of the other tests suggested in post #78? For example, checking slack in the timing chain, etc.

 

I agree. Lack of advance will just reduce power, but not cause a miss. Basically, the explosion is happening after the piston is part way down, so you don't get the full impact.

 

Haven't checked chain slack but this engine has less than 25k miles on a full professional rebuild. I don't think they would have reused a sloppy chain but who knows. I will check this.

As for post #78, I haven't changed plugs again yet nor checked AC ripple. Plugs were changed once with no help, and filter was changed once, also no help.

 

Well fellas it is not the plugs; replaced new Autolite 25 with Motorcraft ASF42C, gapped @ .045. It is not the plug wires; replaced semi-old Motorcraft wires with new Belden Premium. Neither changed anything, still bogging/stuttering on acceleration on a steep hill.
And just for KR, chain slack is less than 5 degrees. Still looking!

 

What about a distributor with bad bushings? That would let it wobble or chatter at certain RPM's and the spark timing would be all over the map.

 

Just as you suggested, the next step is to pull the distributor and check it from end to end, bushings, advance weights, springs, etc.

While I am in there I may as well re-curve it if the distributor is in good enough shape to warrant the effort. Other than Mr. Gasket and Crane, I can't find any other advance spring kits for Duraspark. Crane includes the adjustable vacuum advance, which may be a good thing, but sure jacks the price up if all you need is springs. Anyone know of any other distributor spring kit where the springs might be adaptable?

If the distributor is otherwise defective, it is time for a different distributor. I'm just not sure whether to consider an HEI or just get a re-curved Duraspark from Scott at Re in "Car" nation High Performance

 

I've seen a lot of problems with the HEI's. Maybe only those with problems post about their HEI, but it gives me pause for concern.

And, I don't like Mr. Gasket for anything. Their stuff is of poor quality from what I've seen. I'd go Crane.

 

might ask where you found a new horseshoe connector? I had been looking for one for a long time.