The Stovebolt Site Forums The Shop Area Engine Shop Out of nowhere rough runner

I have a ‘59 Apache with a 235 that I use as my daily driver. It has always run well until the other day and now I’m stumped.

I was driving and everything was fine, then out of nowhere the truck starting bucking upon acceleration. I limped it home and found that it idled ok, but with a hint of a misfire. I checked the fuel delivery and it was fine. I then checked the plugs and they were dry fouled with soot. I changed the plugs and went for a test drive. No more misfire, but the truck wanted to run rough unless the choke was about halfway out. Came home and pulled the distributor cap. Cap looked good, but the rotor was a bit rough. I checked my points gap and saw it was way too close (.004”). Reset the gap to .016” and changed the rotor. The truck fired right up and ran great. Test drive went really well.

The next day (today) I drive the truck about 20 miles and it started acting up again. Pulled the plugs and saw they were starting to foul again. Rechecked the point gap and it was still good. Decided to go ahead and replace the points anyway, just in case. Noticed the air filter was a bit dirty, so went ahead and replaced it too (thought lack of air might be making things run rich).

Fired it back up and it idles fine, but upon revving it is shaking and does not sound right. I can’t tell if this is a combination of issues or one issue has exposed the other. Any help or advice would be appreciated. Thanks.

How long have the spark plug wires been on the engine? Modern non-metallic "wires" deteriorate over time and develop very high resistance that can cause an intermittent miss under load. Try checking the wires with an ohmmeter. There should be no more than 1,000 ohms per inch- - - -for instance, a 12" wire shouldn't have more than 12,000 ohms. A wire bad enough to cause a miss under load will have much more. Good luck!
Jerry

Jerry,

Thanks for the info. The wires are about 3-4 years old. I’ll check the resistance of them in the morning. Assuming they’re good, where do I go next? I was thinking maybe the carb, but the truck’s idling fine. I also don’t want to mess with too many parts at the same time. I still can’t figure out what’s causing the plugs to foul so quickly. Thanks again.

Hmmmmm- - - - -I posted another comment, but the forum ate it, I guess. Check the power valve in the carburetor. If you're running a Rochester B they're notorious about the vacuum piston sticking and holding the power valve in the full rich position. That makes for lousy gas mileage, rough running, and fuel-fouled spark plugs.
Jerry

Yup, it’s the Rochester B. I’ll check it tomorrow as well.

By the way, do you have to check the timing every time you replace the points, or no?

This issue always seems to be difficult to fix. So many things can cause and all we have is a description. I'll take a stab and add to the already given causes. Keep in mind we chase this issue all the time. It may take awhile or you may get lucky right away. Keep exact info coming.

No need to check timing when changing points. But after a few days we may say "check timing".

Cleaned air cleaner? What kind? Hope it's not a 4" diameter paper filter hot rod one. Running rich? I think lean. If it needs choke on it means it's running lean. Needs more gas, less air. If it is not rich, then the black plugs are a spark issue. (and that's a another half dozen causes). Don't look at the plugs anymore. Soot is not a worry, it's temporarily caused by whatever is wrong, carbon buildup, gas wet or oil is of more concern.

Drives bad and you discover .004 points gap? Don't think it would have run with .004. I am disregarding that info.

Changed points, runs good for awhile?
When a truck runs one day and not the other and it needs choke to run under load, there are things that can change each day, but NUMBER ONE is clogged gas delivery. Gas tank dirt floating around blocking tank pick up, fuel lines clogged, fuel filters clogged...........and of course, fuel pump going out, intermittent vacuum hose leak, intermittent accelerator pump, intermittent condenser........and here we go.

Keep in mind that whatever I left out is what is really wrong. I am 100% sure.

Anytime the point gap changes, the timing changes with it. For every one degree of "dwell" change (the amount of distributor rotation the points are closed) the timing at the crankshaft changes two degrees. If your point dwell (gap) is changing rapidly, something else is wrong. There could be a worn bushing in the distributor, or simply a "soft" rubbing block on the points or a rough distributor cam that's wearing the rubbing block away rapidly.

As with any other diagnostic process, eliminate possible problems one at a time instead of rushing off in all directions. Good luck!
Jerry

All good suggestions. So it's a daily driver and ran great then out of the blue it's running bad.. And needs partial choke to smooth out.
1) I had a similar problem, the coil wire had come loose and was dangling down below the coil (it's upside down). Could also be a bad coil to dist wire, replace it with a known good one for testing.
2) check all manifold and carb bolts for tightness. All are known to loosen over time. (sounds like it's sucking air).
3) Do you have a separate fuel filter? if so replace it.
4) Verify you're getting good "squirts" of fuel from the fuel pump. Disconnect the fuel line at the carb and aim it into a glass jar or similar, have some one crank the engine It's OK if it starts, it won't run long). You should see a good squirt of fuel. It'll be on/off based on when the pump is pulling fuel then pumping fuel.
5) Pull the carb and go through it. Jerry mentioned the power valve could be sticking, the float could have a restriction or crud is in the passages.

Did you install a new condenser when you changed the points? I had a rough running car years ago that was giving me fits, and that's what fixed it. Only time that has ever happened to me anyway.

The truck is once again running well........for now (I'll keep my fingers crossed). Here's the summary of what was done:

Day 1
-Checked fuel delivery - Sat
-Replaced spark plugs
-Checked distributor cap - Sat
-Replaced rotor
-Reset gap on existing points

Day 2
-Replaced points and set gap
-Replaced air filter

Day 3 (today)
-Checked resistance of spark plug wires - Sat
-Checked resistance of coil - Sat
-Checked for vacuum leaks - Sat
-Checked carb - Sat
-Checked and adjusted points spring tension (it was really low)
-Replaced condenser

The truck started up and ran great. I took it for a nice drive, up and down hills, and also ran it close to top speed with no issues. Everything appears to be fixed, but it ran well between days 1 and 2, so I guess time will tell. Maybe one of these parts was having an intermittent fault and, hopefully, has now been replaced. Thanks to all for the helpful input. I'll report back if anything changes. Thanks again.

Mike

Although it could have been anything, the simple condenser/capacitor is a big part of the equation. It explains it's important function in this article. It's a very small .2 microfarad capacitor from the 2 I have that I checked, that is important for the system to work.
https://en.wikipedia.org/wiki/Ignition_system