Posted by Alan Bowes on December 08, 1998 at 09:38:48:
In Reply to: truck ran great, now runs badly 54 M-37 posted by scott W. on December 03, 1998 at 15:55:49:
Well Scott, the symptoms you listed are a bit sketchy. If you could provide a little more detail, it would help. Sounds like it might be ignition related, but hard to say. With a conventional ignition system, the spark will tend to get weaker as RPM increases, and if your ignition is already borderline, it will often start to miss as engine speed increases. A borderline ignition will also make it harder to start. All of the following (and then some) could contribute to a weak spark:
Misadjusted points.
Incorrect timing.
Problem with centrifugal advance.
Faulty coil.
Shorting ignition capacitor or shorting filter capacitor.
Wear in distributor shaft and cam assembly.
Coil with shorted internal windings.
Rust deposits in spark plug cable connectors or inside the upper sparkplug insulator.
Bad spark plug cables (more typical with carbon-type conductors).
Fouled spark plugs or metallic film on ceramic insulator from using a wire brush to clean the plugs.
Carbon tracks on top of coil or in distributor cap or on rotor.
Loose connections and corrosion. Check the pin on the +24V receptacle on the outside of the distributor (these often develop a corrosion layer).
Etc.
I wouldn't rule out carburetion problems either, but check the igntion and timing first.
Again, if you can provide more details on how it behaves, it would help. For example, once it is started, does it run OK at low speeds? Does it miss under both light and heavy loads? Can you hear it miss when you're holding it at different engine speeds with the vehicle in neutral? Can you see any black smoke? If so, when? Etc. Etc.
Good luck,
Alan