Make sure you have proper voltage at the ignition coil. This kind
of problem is often a symptom of an electrical component heating
up and causing a problem. Rig a wire from the "+" terminal on the
ignition coil to a voltmeter on the passenger seat. Find a good
ground contact for the voltmeter "-" lead. Notice the voltage
when you first have it running, probably around 8-9 volts if you
are using the original coil that has an external ballast resistor
mounted on the firewall. When it starts to run lousy, check the
voltage.
If the voltage drops when the engine starts acting up, common
culprits are:
faulty ballast resistor (test by checking voltage in & out)
faulty tachometer (test by disconnecting)
faulty key switch (test by jumpering around it)
faulty electrical harness (test by wiggling stuff, jumpering)
If the voltage is OK, test the spark strength of each cylinder, in
turn, using a spark tester with about a 1/4"-5/16" gap, running the
engine each time on the other 3 cylinders. This lets you see if the
spark is strong and steady.
I wouldn't just start replacing all kinds of stuff without nailing
down what is causing the problem. Gets frustrating and expensive.
And I sure wouldn't rip into the carbs unless I knew they needed it.
Carl Wade
Williamson, New York State USA
B395000858 LRX
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