Engine runs rough for a short time

[72f250CSmallardgreen]

To make a long story even longer...
I bought my 1971 f250 (camper special, 360, c6, 2 barrel) back in march of this year (2018). It is currently my daily driver. From day one, I had an occasional engine misfire. It would run a little rough and was very slow and jittery when it accelerated. I set the timing to 10 and tuned the carburetor. I put on a new coil, pertronix, plugs, wires, and cap but did not solve the problem. A little while back, whatever holds the plate down in the distributor got loose in the distributor and melted my pertronix magnetic ring. It also looked like it melted the piece that holds the plate down and the plate would move wherever it wanted in the distributor. It still ran but I wanted to get the problem fixed. I bought an autozone distributor (piece of crap) in order to get it on the road the next day. I still have that autozone distributor in with the old coil and points. I still have the engine misfire. I was told by a mechanic that it was probably valve seals and that I should do a compression test. I borrowed a friends gauge and got the following results: 1:86, 2:70, 3:60; 4:75, 5:71, 6:65, 7:85, 8:65. I still have not had the chance to test them with a squirt of oil. On my way home from work today my truck started running like it was out of gas. It was surging bad and i had to keep pumping the gas to keep it running. I ran it for about a quarter mile until i found a driveway to pull into. In that time it backfired twice (like gunshots) and could barrely make it up the slight hill i was driving on. It died when i pulled into the driveway. I looked at the distributor and it looked like it was a little bit advanced. It took all my might to twist that thing but i got it to move a little bit counterclockwise. It started right up but died 30 seconds later. I fooled around for 5 minutes and could only keep it running if i kept pumping the gas. All of the sudden, it leveled out and ran like before. I drove it ten miles home withought any other incedent. I am slightly scared to drive it now because i do rely on it to bring me to the jobsite each day. Does anybody know what could cause this brief loss of power? What can i do to fix it?
Thanks,
Dave

[fastEdsel]

Is it the original engine? How many miles? I would check the timing chain at this point.

[jzjames]

Have you thought it could be a fuel issue?
Carb, fuel pump.filter, gas tank.

[cep62]

Also check for power to the coil with a volt meter when it happens .
There's a resistor wire under the dash (pink if recall correctly) that limits the voltage to the coil to save the points.
It's not used in the starting position, so your truck will start and stall.
Sometimes it'll run awhile.
As a test next time it stalls get a jumper wire and clip it to the + coil and battery.
But be careful you won't be able to stop the engine until you pull the wire off.

[72f250CSmallardgreen]

Thanks for the help guys,
I drove it about 5 miles today without any problems.

Its the original engine with 105,000 on it. I think that the previous owner took it to get the oil changed by the dealer so the oil did not have a zinc additive. I want to hold off on the timing chain because I think I will be performing a rebuilt within the next year anyways.

I don't think it is a fuel issue. I did buy fuel the day before but I drove at least 15 miles since then before it had the problem. So I don't think its a fuel quality issue. When I would pump the gas during the time it would run poorly, I got two steady streams of fuel. I drained and flushed the gas tank since I bought the truck. The tank was at least 3/4 full too. I recently replaced the fuel filter with a summit racing cheapo.

I will try to check the voltage to the coil next time it happens. I know that when I installed the pertronix originally, I checked the voltage in the key on position and got 12 volts. I did not look to remove the pink wire because I was getting the twelve volts I needed.

Thanks again
Dave

[sargentrs]

I will try to check the voltage to the coil next time it happens. I know that when I installed the pertronix originally, I checked the voltage in the key on position and got 12 volts. I did not look to remove the pink wire because I was getting the twelve volts I needed.

Check the voltage with the engine running. The resistor wire comes into play to reduce the voltage to the distributor so as not to burn up the points. If you didn't bypass it when you installed the Pertronix, it's probably not getting the full 12v when running.

[72f250CSmallardgreen]

So about a week ago, it happened again. When I tried to start it, I could just barely keep it running after cranking for a long time. A lot of backfiring. I have not had time to monkey with it until this afternoon. I have 6.2 volts at the coil with the key on. (12.7 battery volts) I know I have consistent spark (according to my timing light). I tried the jumper wire but it made no difference. I could not get my engine to turn fast enough to see what the timing is in the dark. I tried switching to my original distributor with the old pertronix which I know that my engine will run off of. I had the same problem. I might try to throw the battery on the charger and check the timing tomorrow when my dad is around to give me a hand. I am thinking at this point that it has to be a timing chain?
Any other thoughts?
There is not really a rush to get this done because it will be sitting all winter(even though I hope to move it to storage).
Thanks for all the help!
Dave

P.S: I am sure that my truck wouldn't be half of what it is without the Fordification resource

[sargentrs]

6.2v at the coil with key on won't do it if you have electronic ignition, she needs the full 12v. Pull your distributor cap off and rotate the engine by hand while you watch the rotor turn. If you can rotate the engine more than a degree or two in either direction before the rotor moves you have too much slack in the timing chain. Then turn the engine over under power while you watch the rotor. It should rotate smoothly and consistently without hesitating or jerking. If so your timing chain and possibly your gears gave substantial issues. If all that looks good go back to basics. Set your #1 piston on TDC on the compression stroke. Put your #1 plug wire on the distributor cap where the rotor is pointing then install the rest of your wires CCW in the correct firing order. See if she cranks and runs, even roughly, without backfiring. If she will, slowly rotate your distributor until she smooths out. Forget the timing light for now, just see if she'll maintain a smooth idle.

[71cc]

With less than 125 psi I don't understand how it runs at all. Did you hold throttle open while checking compression ?

[72f250CSmallardgreen]

I know this may sound like a dumb question, but how would one go about turning the engine over by hand. I looked into doing that before but the fan shroud was blocking any sort of sizable breaker bar from fitting. Is there an easier way?
As far as the compression, I was pretty scared when I took the readings myself, but the engine still runs. I'm pretty sure that my gauge is accurate because its an older SUN that is in pretty good shape. I was hoping to do the valve seals this winter, but the heated shop that I could use/ store it in is 15 miles away and now that my truck wont run....

Thanks for the quick responces
Dave

[sargentrs]

I know this may sound like a dumb question, but how would one go about turning the engine over by hand. I looked into doing that before but the fan shroud was blocking any sort of sizable breaker bar from fitting. Is there an easier way?

Can you get to the harmonic balancer bolt from underneath? Fan shrouds usually have more clearance at the bottom because of the radiator hose. If not that, maybe by turning the fan or putting a socket on the alternator or P/S pump? Might have to tighten the belts for traction. You only need to move it a little to see how far the engine turns before the rotor moves.

[72f250CSmallardgreen]

Recap:
I just finished my rebuild. All went well. I cant say that I know what the problem was for sure, but I am guessing it was the timing chain. It was hard for me to tell how much slop was in the chain by rotating the engine by hand. When I pulled the cover off, the chain had at least 3/4 inch of play in it. Also, the plastic timing gear was somewhat rounded over (at least compared to my new set). I am guessing that the timing set was the problem. Another potential reason could be the points (I doubt it). When we went to start then engine for the first time, we spent a lot of time diagnosing a bad set of points. If I remember correctly, those points were never quite seating properly against each other from the start. I am still running that junky duralast distributor, but hope to change it to MSD (My machinist highly recommended it) in the next year or so. Sorry for the late response but I just finished my motor a month ago and didn't want to give a recap until I was sure that all my problems were fixed. Thanks again for all the help. Fortification truly is the best.
Dave