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A vacuum leak will cause fluctuating idle speed. Check carburetor bolts are snug. Check all hoses going to carburetor and intake. Pinch closed with pliers, see if changes.


Clean or replace as needed the plugs, wires, cap and/or rotor.

Set valve lash at 0.010 intake and 0.012" exhaust when HOT.

Timing at 12 BTDC.



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It may be for an '80 so always go with the FSM. All other years of L series are 10 and 12 thou.


All '78 '79 and '80 L20Bs use the W58 head so I don't see any difference.

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20 hours ago, Donki said:

The truck sat for 3 years new plugs wires cap rotor ignition coil coil starter fuel  filter cleaned carb runs good at high revs let off gas it pops out of exhaust smells bad then dies 



High revs under load, like when driving it? or just revving it up??? Big difference if under a load.

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