xHighOctanex Posted December 13, 2015 Report Share Posted December 13, 2015 Hello, I just got an 84 King cab 720. The motor that came with it came out of a different 720 that ran like complete crap, it would misfire pretty bad and then at about 45mph it would get worse and you had to push it pretty hard to go any faster. I pulled the head off expecting either the head to be blown or the pistons to be in bad shape, but everything looks pretty good. 2 cylinders ran lean but other than that the head looks fine, cylinders are all very clean looking, pistons look fine. I want to just do maybe a ring kit and gaskets, but is there anything I am missing? Quote Link to comment
datzenmike Posted December 13, 2015 Report Share Posted December 13, 2015 Why pull the head? Some other things need to be checked and eliminated first. You need spark and fuel and generally some compression. What did a compression test reveal? If some low readings, did you then check the valve lash? Tight valves can't close properly and compression is not sealed in. Spark... Ignition wires and plugs. Distributor cap is small with 8 wires very close together and easy for a spark to jump to another wire or ground. Worn rotor? Hows the timing? about 5 degrees? Fuel... Replace fuel filter? If clogged, the carb will empty and run out of gas faster than the gas can be pushed through it. Gets worse under load. Choke stuck on? will limit performance, top speed and give terrible mileage. Primary jet part clogged forcing a lean condition under load and loss of power and performance. Other... crushed tail pipe. collapsed muffler. These are just a few things that need checking before head removal or rebuilding is both a wa$te of time and won't fix it. Quote Link to comment
Nissan_Boy85 Posted December 13, 2015 Report Share Posted December 13, 2015 Even just checking that the right plug wire is on the right plug is a good starting point. Plugs could also have cracks in them. Quote Link to comment
datzenmike Posted December 13, 2015 Report Share Posted December 13, 2015 Good one. There's 4 per side. 4 intake and 4 exhaust arranged int/ex/int/ex and so on around the cap. The stock cap has the order stamped beside each plug terminal. Easy to mix up. Here's another thing.... Although both plugs in each cylinder fire together only one is powered directly from the ignition switch.The exhaust coil is powered through the fuse box, so if the fuse blows you are only running on a single plug per cylinder. This increases the burn time and the engine acts like the timing is retarded. Replace the second fuse over from the left side of the fuse box. 1 Quote Link to comment
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